FUNCTIONAL AND PATTERNABLE
ELECTRO-GRAFTED COATINGS
A Dissertation
Presented to
the Faculty of the Department of Chemistry
University of Houston
In Partial Fulfillment
of the Requirements for the Degree
Doctor of Philosophy
By
Edward Lee Foster
August 2012
ii
FUNCTIONAL AND PATTERNABLE
ELECTRO-GRAFTED COATINGS
______________________________________________
Edward Lee Foster
APPROVED:
______________________________________________
Dr. T. Randall Lee, Chairman
______________________________________________
Dr. Rigoberto C. Advincula
______________________________________________
Dr. Ognjen S. Miljanic
______________________________________________
Dr. Roman S. Czernuszewicz
______________________________________________
Dr. Gila E. Stein
______________________________________________
Dr. Mark A. Smith, Dean
College of Natural Sciences and Mathematics
iii
ACKNOWLEDGMENTS
I am grateful to all of those with whom I have had the pleasure to work with during my
entire time in graduate school.
To my committee members, Dr. Lee, Dr. Czernuszewicz, Dr. Miljanic, and Dr.
Stein, for their encouraging words, thoughtful criticism, time, and attention.
To my advisor, Dr. Rigoberto C. Advincula, who gave me the opportunity to learn
and for his guidance.
To the past members of the Advincula group Rams, Yushin, Antonello, Jin,
Lalithya, Guoqian, Rod, Jane, Nicel, Subbu, Deppali, and Cel for all of their support; to
the present members Katie, AJ, Joey, Kim, Pengfei, Al, Brylee, Kat, and Allan for
participating in my learning experience.
To my parents Dr. James Lee Foster and Anita Foster for all their guidance.
To Lynn Tarkington for her love and support.
iv
FUNCTIONAL AND PATTERNABLE
ELECTRO-GRAFTED COATINGS
An Abstract of a Dissertation
Presented to
the Faculty of the Department of Chemistry
University of Houston
In Partial Fulfillment
of the Requirements for the Degree
Doctor of Philosophy
By
Edward Lee Foster
August 2012
v
ABSTRACT
The use of electro-grafted materials provided a quick and efficient route to
functionalize conducting surfaces. The unique properties of electroactive materials allow
for large surface areas to be covered by the material being deposited. Chapter 1 reviews
recent developments and practices in the use of electro-grafted materials. Chapter 2
reports the fabrication of patterned binary polymer brushes via colloidal particle
templating combined with electrodeposited atom transfer radical polymerization (ATRP),
reversible addition fragmentation chain transfer radical polymerization (RAFT), and ring
opening metathesis polymerization (ROMP) initiators. Chapter 3 demonstrates a new
approach of creating topologically and well-defined patterned polymeric surfaces via the
“grafting to” approach. This was accomplished by either using colloidally templated
“clickable” arrays, whereby the chemistry was performed directly onto the pattern or by
subsequent backfilling with azido terminated self-assembled monolayers (SAM).
Similarly, direct grafting of electroactive temperature-responsive oligo(ethylene glycol)
methacrylic polymers to colloidally templated surfaces allowed for tunable ion gate
formation. In chapter 4, a novel one step approach to fabricate superhydrophobic and
superoleophilic coatings is reported. Due to the incorporation of an ATRP moiety into the
coating, surface initiated ATRP (SI-ATRP) was performed to change the wettability of
the substrates towards a variety of liquids. Chapter 5 reports the fabrication of
polymerizable superhydrophobic coating by using a facile one step procedure i.e.
electrodeposition. These coating exhibited tunable bacterial adhesion, self-cleaning
vi
capabilities, and corrosion resistance. Similarly, surface initiated ATRP of
3,3,4,4,5,5,6,6,7,7,8,8,9,9,10,10,10-heptadecafluorodecyl methacrylate (HDFM) was
performed on a steel slide. Subsequent static water, diiodomethane, and hexadecane
contact angles revealed that the steel coated surface was now superamphiphobic. In
chapter 6 the fabrication of pendant terthiophene polymer brushes and their application as
ultrathin films is demonstrated. Ellipsometry and atomic force microscopy (AFM) studies
showed differences in the film structure at various stages of film development. These
films were subsequently employed for the investigation of electrochemical
nanopatterning using current sensing AFM as a writing technique. The pattern formation
was demonstrated in order to show the possibility for future applications, such as
information storage devices and nanowires. Finally in chapter 7, conclusions,
perspectives, and future work based on chapters 2-5 is presented.
vii
TABLE OF CONTENTS
Acknowledgments iii
Abstract v
Table of Contents vii
List of Figures xv
List of Schemes xxiv
List of Abbreviations xxv
Chapter 1. Introduction 1
1.1. General Principles of Electropolymerization 2
1.1.1. Mechanisms 2
1.1.2. Electro-grafting 3
1.2. Electro-grafting of Polymerizable Electroactive Monomers and
Polymer Brushes
4
1.2.1. Reversible Addition Chain Transfer Radical Polymerization 6
1.2.2. Atom Transfer Radical Polymerization 9
1.2.3. Ring Opening Metathesis Polymerization
11
1.2.4. Click Chemistry 13
1.3. Surface Patterning 17
1.3.1. Colloidal Templating 17
1.3.2. Patterning with Scanning Probe Technques 24
1.4. Electroactive Materials as Viable Coatings for Anti-wetting 26
viii
Characteristics
1.4.1. Templating Approach 29
1.4.2. Template-Free Method 32
1.5. Chapter Outlines and Objectives
35
1.6. References 37
Chapter 2. Patterned Polymer Brushes
Electrodeposited ATRP, ROMP, and RAFT Initiators on Colloidal
Template Arrays
51
2.1. Introduction 51
2.2. Results and Discussion 54
2.2.1. Formation of Inverse Colloidal Cbz-intiator Arrays 54
2.2.2. Surface Initiated Polymerization of MMA via ATRP 57
2.2.3. Formation of Inverse Colloidal Cbz-CTA and Cbz-Nb Arrays
61
2.2.4. Patterned Binary Brush Surface via ATRP and RAFT
Polymerization
64
2.3. Conclusions 68
2.4. Experimental
69
2.4.1. Materials 69
2.4.2. Instrumentation 69
2.4.3. Surface Preparation
71
2.4.4. PS Monolayer Formation and Removal
71
2.4.5. Surface Initiated ATRP 72
2.4.6. Surface Initiated RAFT Polymerization 73
ix
2.4.7. Surface Initiated ROMP 73
2.4.8. Synthesis 73
2.5. References 74
Chapter 3: Click Chemistry and Electro-grafting onto Colloidally
Templated Conducting Polymer Arrays
3.1. Introduction 77
3.2. Results and Discussion 81
3.2.1. Synthesis of PS-N3 and PS-Alkyne 81
3.2.2. Formation of Inverse Colloidal Cbz-Alkyne Arrays 83
3.2.3. Grafting of PS-N3 onto Inverse Colloidal Cbz-Alkyne Arrays 85
3.2.4. Formation of Inverse Colloidal Cbz-TEG Arrays 88
3.2.5. Temperature-responsive PPEGMEMA 91
3.3. Conclusions 97
3.4. Experimental 97
3.4.1. Materials 97
3.4.2. Polymerization of Styrene to Form of PS-Br 98
3.4.3. Synthesis of PS-N3 98
3.4.4. Synthesis of CTA-Alkyne 99
3.4.5. Polymerization of Styrene to Form of PS-Alkyne 99
3.4.6. Synthesis of Cbz-CTA 99
3.4.7. Polymerization of PEGMEMA to Form Cbz-PPEGMEMA-
CTA
99
3.4.8. Surface Preparation and Electrodeposition 100
x
3.4.9. Copper-catalyzed Click Reactions 101
3.4.10. Synthesis of Electroactive Monomers and 9-azidononane-1-
thiol
102
3.4.11. Characterization 102
3.5. References 103
Chapter 4: Electropolymerized and Polymer-grafted
Superhydrophobic, Superoleophilic, and Hemi-wicking Coatings
4.1. Introduction 109
4.2. Results and Discussion 112
4.2.1. Film Fabrication and Characterization 112
4.2.2. Surface Initiated ATRP of NIPAM 119
4.2.3. Formation of Oleophobic Surfaces 123
4.3. Conclusions 125
4.4. Experimental 125
4.4.1. Materials 125
4.4.2. Surface Preparation 126
4.4.3. Electrodeposition 126
4.4.4. Surface Initiated ATRP 127
4.4.5. Synthesis 127
4.4.6. Characterization 128
4.5. References 129
xi
Chapter 5: Tunable and Polymerizable Multifunctional Electroactive
Coatings
5.1. Introduction 134
5.2. Results and Discussion 137
5.2.1. Film Formation 137
5.2.2. Superhydrophobic Composites with Different Functional
Groups
139
5.2.3. Tunable Wetting Behavior 141
5.2.4. Steel Optimization and SI-ATRP 146
5.2.5. Corrosion Studies 151
5.3. Conclusions 155
5.4. Experimental 156
5.4.1. Materials 156
5.4.2. Surface Preparation 157
5.4.3. Electrodeposition 158
5.4.4. Surface Initiated ATRP 158
5.4.5. Synthesis of 3T-CTA 158
5.4.6. Synthesis of 3T-Alkyne 158
5.4.7. Synthesis of 3T-Nb 159
5.4.8. Bacterial Adhesion Measurements 159
5.4.9. Statistical Analysis 160
5.4.10. Characterization 160
5.5. References 161
xii
Chapter 6: Nanopatterning of Terthiophene Pendent Polymer Brushes
6.1. Introduction 168
6.2. Results and Discussion 172
6.2.1. Substrate Modification and Characterization 172
6.2.3. Patterning 175
6.3. Conclusions 184
6.4. Experimental 185
6.4.1. Materials 185
6.4.2. Surface Preparation 185
6.4.3. Electrodeposition 186
6.4.4. Surface Initiated RAFT Polymerization 186
6.4.5. Synthesis of 3T-CTA 187
6.4.6. Synthesis of 3T-Methacyrlate 187
6.4.7. Characterization 187
6.5. References 187
Chapter 7: Conclusions and Future Work
7.1. Introduction 191
7.2. Future Work 193
7.3. Final Remarks
194
Appendix I: Additional Information for Chapter 2
AP.I.1. Synthesis Methyl 3,5-bis(4-(9H-carbazol-9-yl)butoxy)benzyl
Alcohol (Cbz-OH) and 3,5-Bis[4-(9H-carbazol-9-yl)butoxy]benzoic Acid
195
xiii
(Cbz-COOH)
AP.I.1.1. 9-(4-bromobutyl)-9H-carbazole (Cbz-Br) 196
AP.I.1.2. Methyl 3,5-bis(4-(9H-carbazol-9-yl)butoxy)benzoate
(Cbz-COOCH3)
196
AP.I.1.3. Cbz-OH 197
AP.I.1.4. Cbz-COOH 198
AP.I.2. 3,5-bis(4-(9H-carbazol-9-yl)butoxy)benzyl 2-bromo-2-
methylpropanoate (Cbz-Initiator)
198
AP.I.3. Synthesis of 3,5-bis(4-(9H-carbazol-9-yl)butoxy)benzyl-4-cyano-4
(phenylcarbonothioylthio)pentanoate (Cbz-CTA)
199
AP.I.4. Synthesis of Bicyclo[2.2.1]hept-5-en-2-yl-methyl 3,5-Bis- (4-(9H-
carbazol-9-yl) butoxy)benzoate (Cbz-Nb)
201
AP.I.5. Synthesis of 11-(2-bromo-2-methyl)-propionyloxy)-undecyl-
trichlorosilane (ATRP-Silane)
202
AP.I.5.1. 10-Undecen-1-yl 2-Bromo-2-methylpropionate (ATRP-
Olefin)
202
AP.I.5.2. ATRP-Silane 203
AP.I.6. References 203
Appendix II: Additional Information for Chapter 3
AP.II.1. Synthesis of 3,5-Bis[4-(9H-carbazol-9-yl)butoxy]benzoic Acid
(Cbz-COOH)
205
AP.II.2. Synthesis of 2-(2-hydroxyethoxy)ethyl 3,5-Bis(4-(9H-carbazol-9-
yl)butoxy)benzoate (Cbz-TEG), and prop-2-ynyl 3,5-Bis(4-(9H-carbazol-9-
yl)butoxy)benzoate (Cbz-Alkyne)
205
AP.II.2.1 Synthesis of Cbz-TEG
206
AP.II.2.2 Synthesis of Cbz-Alkyne
207
xiv
AP.II.3. Synthesis of 9-Azidononane-1-thiol
208
AP.II.4. References
208
xv
LIST OF FIGURES
Figure 1.1. Synthetic strategies for the preparation of polymer brushes
via chemisorption reaction of end-functionalized polymers
with complementary functional groups at the substrate
surface.
5
Figure 1.2. Synthetic strategies for the preparation of polymer brushes
grown via SIP technique.
6
Figure 1.3. General route for preparing polymer brushes from an
electro-grafted terthiophene CTA.
7
Figure 1.4. General outline for the preparation of protein and cell-
resistant PPEGMEMA brushes from the electrodeposited
RAFT agent.
8
Figure 1.5. Grubbs’ first and second generation catalyst 1 and 2 (Cy =
cyclohexyl).
12
Figure 1.6. Polynorbornene brushes synthesized via surface initiated
ring opening metathesis polymerization (SI-ROMP).
13
Figure 1.7. Synthesis of PS-pyrrole and PS-thiophene by click reaction. 15
Figure 1.8. Structure of poly-1 and synthesis of poly-3. 16
Figure 1.9. (a) Schematic illustration of the procedure used for
fabricating PANI inverse opal microstructures via
electropolymerization within a PS colloidal crystal on top of
a gold electrode. SEM-images of the (b) colloidally
templated gold surface and (c and d) PANI inverse opals
with two different magnifications.
18
Figure 1.10. AFM 2D topography images (3D inset) of the (a) PS-coated
substrate and (b) molecularly imprinted and templated
surface before norephedrine removal.
19
Figure 1.11. AFM topography images (3D inset) of a 500-nm backfilled
templated array ((a) 5 μm × 5 μm and (b) 2 μm × 2 μm
scans), along with (c) line profile analysis before and after
backfilling with 1-ODT. (d) High resolution XPS scan of S
2p peak.
20
xvi
Figure 1.12. Structures of (a) 3,5-bis(4-(9H-carbazol-9-yl)butoxy)benzyl
2-bromo-2-methylpropanoate (Cbz-Initiator), (b) 3,5-bis (4-
(9H-carbazol-9-yl) butoxy) benzyl 4-cyano-4
(phenylcarbonothioylthio) pentanoate (Cbz-CTA), and (c)
Bicyclo[2.2.1]hept-5-en-2-ylmethyl 3,5-Bis- (4-(9H-
carbazol-9-yl) butoxy) benzoate (Cbz-Nb). Structures of (d)
prop-2-ynyl 3,5-bis(4-(9H-carbazol-9-yl)butoxy)benzoate
(Cbz-Alkyne), (e) 2-(2-(2 (2-hydroxy)ethoxy)ethoxy)ethyl-
3(4-(9H-carbazol-9-yl)butoxy)-5-(4-(9Hcarbazol
9yl)butoxy)) benzoate (Cbz-TEG), (f) electroactive
dendritic-linear PPEGMEMA (Cbz-PPEGMEMA-CTA)
molecule, (g) linear PS with terminal azide functional group
(PS-N3) and, (h) linear PS with terminal alkyne functional
group (PS-Alkyne).
22
Figure 1.13. Fabrication of a highly ordered monolayer of colloidal
arrays (500 nm diameter PS microspheres), inverse colloidal
arrays, and patterned polymer brushes via the “grafting to”
approach using linear (Route 1) PS-N3, (Route 2) PS-
Alkyne or, (Route 3) Cbz-PPEGMEMA-CTA polymers.
23
Figure 1.14. CS-AFM nanopatterning of a “nanocar” on a a Cbz
containing film at 10 V with a writing speed 0.8 µm/s (a)
topographic image and (b) current image. The current image
was obtained by scanning at 1 V after the patterning. Color
bar range is 0−14.7 pA.
26
Figure 1.15. Photographs of the (a and b) of the lotus leaf, (c) butterfly,
(d) and water strider.
27
Figure 1.16. Wetting states (a) Wenzel, (b) Cassie–Baxter. 28
Figure 1.17. Contact angle measurements of poly(3T-COOR) onto 500
nm PS/Au in (a) water, (b) diiodomethane, and (c)
hexadecane. (d) Low 24 μm × 36 μm and (e) high
magnification SEM images of poly(3T-COOR) onto 500 nm
PS/Au at 4 μm × 3 μm.
30
Figure 1.18. (a) Photograph of the Xanthosoma Sagittifolium leaves. (b)
SEM image of the leaf. (c) SEM images of the imprinted
layers of SEE showing a top view of the surface. (d) SEM
images of the imprinted layers of SEE showing a cross-
section view of the surface.
31
xvii
Figure 1.19. (a) SEM image of the rambutan-like hollow PANI spheres
(inset a photograph of a rambutan). (b) Shape of a water
droplet on a surface of the rambutan-like PANI hollow
spheres.
33
Figure 1.20. Structures of electroactive monomers: (a) pyrole, (b)
ethylenedioxypyrole, (c) propylenedioxypyrole, (d)
thiophene, (e) ethylenedioxythiophene derivatives.
34
Figure 1.21. SEM images of electro-grafted polymers from (a) side (b)
and top view.
35
Figure 2.1. Structures of (a) 3,5-bis(4-(9H-carbazol-9-yl)butoxy)benzyl
2-bromo-2-methylpropanoate (Cbz-Initiator), (b) 3,5-bis (4-
(9H-carbazol-9-yl) butoxy) benzyl 4-cyano-4
(phenylcarbonothioylthio) pentanoate (Cbz-CTA), and (c)
Bicyclo[2.2.1]hept-5-en-2-ylmethyl 3,5-Bis- (4-(9H-
carbazol-9-yl) butoxy) benzoate (Cbz-Nb).
52
Figure 2.2. (a) General structure of the electro-active functional
initiators before and after electrodeposition forming the
polycarbazole network. (b) Fabrication of a highly ordered
monolayer of colloidal crystals (500 nm diameter PS
microspheres), inverse colloidal arrays, and patterned
polymer brushes via SIP.
54
Figure 2.3. (a) Representative I-T curve of the electrodeposition via
chronoamperometry at a constant potential of 1.3 V for 3
min and the subsequent monomer free scan (inset). (b) UV-
vis spectrum of inverse colloidal Cbz-Initiator arrays after
electrodeposition.
56
Figure 2.4. AFM topography 2D images (2.5 × 2.5 m): (a) 500 nm PS
monolayer array, (b) after electrodeposition of Cbz-Initiator
and washing of PS microspheres (inverse colloidal Cbz-
Initiator arrays), and (c) after 1 hr polymerization of MMA.
Line profile analysis: (d) single PS microsphere, (e) cavity
after electrodeposition of Cbz-Initiator and PS removal, and
(f) before and after SIP of MMA.
58
Figure 2.5. High resolution XPS scan of the (a) C 1s (deconvoluted C
1s PMMA peak in inset) and (b) the O 1s peak of the
patterned film before and after polymerization of MMA. (c)
ATR-IR spectra of the inverse colloidal Cbz-Initiator arrays,
PMMA brush on patterned surface, and PMMA brush on
60
xviii
unpatterned surface.
Figure 2.6. AFM topography 2D images (2.5 × 2.5 m): (a) the inverse
colloidal Cbz-CTA, (b) Cbz-Nb arrays, (c) Cbz-CTA after
SIP of styrene (1 hr long polymerization time), and (d)
norbornene from the Cbz-Nb inverse colloidal arrays (0.5 hr
long polymerization time).
62
Figure 2.7. AFM line profiles before and after polymerization: (a)
styrene from the Cbz-CTA and (b) norbornene from the
Cbz-Nb inverse colloidal arrays. High resolution XPS scans
of the C 1s peaks before and after polymerization of (c)
styrene from the Cbz-CTA and (d) norbornene from the
Cbz-Nb inverse colloidal arrays.
63
Figure 2.8. (a) Fabrication of the binary brush system via a combination
of SI-RAFT polymerization from the inverse colloidal Cbz-
CTA and the SIP via ATRP from the ATRP-silane initiator
immobilized in the cavities of the pattern. AFM topography
2D images (2.5 × 2.5 m): (b) inverse colloidal Cbz-CTA
after back filling cavities with ATRP-silane initiator, (c)
after SIP of styrene from the colloidal Cbz-CTA with
backfilled cavities, and (d) after SIP of MMA from the
ATRP-silane initiator.
65
Figure 2.9. (a) High resolution XPS scan of the signature Br 3d peak of
the ATRP-silane initiator. Line profiles at the various stages
of film fabrication (b) from before and after after backfilling
cavities with ATRP-silane initiator, and (c) after SIP of
styrene from the colloidal Cbz-CTA with backfilled cavities
with ATRP-silane initiator and after SIP of MMA from the
ATRP-silane initiator.
66
Figure 3.1. Structures of (a) prop-2-ynyl 3,5-bis(4-(9H-carbazol-9-
yl)butoxy)benzoate (Cbz-Alkyne), (b) 2-(2-(2-(2-
hydroxy)ethoxy)ethoxy)ethyl-3(4-(9H-carbazol-9-
yl)butoxy)-5-(4-(9Hcarbazol-9yl)butoxy)) benzoate (Cbz-
TEG), (c) electroactive dendritic-linear PPEGMEMA (Cbz-
PPEGMEMA-CTA) molecule, (d) linear PS with terminal
azide functional group (PS-N3) and, (e) linear PS with
terminal alkyne functional group (PS-Alkyne).
78
Figure 3.2. Fabrication of highly ordered of colloidal arrays 80
xix
Figure 3.3. 1H NMR spectra and peak labels for bromine-terminated
polystyrene (PS-Br) and, azido-terminated polystyrene (PS-
N3).
83
Figure 3.4. (a) Representative I-T curve of the electrodeposition via
chronoamperometry at a constant potential of 1.3 V for 3
min and the subsequent monomer free scan (inset). (b) UV-
vis spectrum of inverse colloidal Cbz-Alkyne arrays after
electrodeposition.
84
Figure 3.5. (a) AFM topography 2-D images (4 × 4 m): (a) 500
nm PS particle monolayer array, (b) after electrodeposition
of Cbz-Alkyne and washing of PS microspheres (inverse
colloidal Cbz-Alkyne arrays), and (c) after grafting PS-N3.
Line profile analysis of (d) single PS particle, (e) cavities
after electrodeposition of Cbz-Alkyne and PS microspheres
removal, and (f) Cbz-Alkyne arrays before and after
CuAAC reaction with PS-N3.
86
Figure 3.6. ATR-IR spectra of before and after grafting PS-N3 via
CuAAC reaction to the inverse colloidal Cbz-Alkyne array
from (a) 1250 to 4000 cm-1
and 3100 to 3400 cm-1
(inset).
87
Figure 3.7. AFM topography 2-D images (4 × 4 m): (a) inverse
colloidal Cbz-TEG array, (b) after back filling cavities with
azidoundecanethiol , and (c) after grafting PS-Alkyne via
CuAAC reaction to azidoundecanethiol. Line profile
analysis: (d) inverse colloidal Cbz-TEG array, (e) after back
filling cavities with azidoundecanethiol, and (f) after
grafting PS-Alkyne via CuAAC reaction to
azidoundecanethiol .
89
Figure 3.8. High resolution XPS scans of N 1s peaks before and after
grafting PS-Alkyne to azidoundecanethiol.
90
Figure 3.9.
1H NMR spectra from (a) 0.6 ppm to 8.3 ppm (b) 6.8 ppm to
8.3 ppm. (c) Cyclic voltammetry scan of the
electrodeposition of Cbz-PPEGMEMA-CTA onto
colloidally templated ITO substrate.
94
Figure 3.10. AFM topography images of the inverse colloidal Cbz-
PPEGMEMA-CTA arrays at (a) 22 oC and (b) 70
oC. (c)
AFM line profiles of the inverse colloidal Cbz-
PPEGMEMA-CTA arrays at 22 oC and 70
oC (d) Cyclic
voltammetry comparative scan of inverse colloidal Cbz-
96
xx
PPEGMEMA-CTA arrays at 22 oC and 70
oC.
Figure 4.1. Structures of 2-(2,5-di(thiophen-2-yl)thiophen-3-yl)ethyl 2-
bromo-2-methylpropanoate (3T-Initiator) and terthiophene
(3T).
110
Figure 4.2. Contact angle measurements of 3T film using (a) water (b)
diiodomethane and hexadecane.
113
Figure 4.3. (a) Cyclic voltammetry diagram of the electrodeposition of
3T/3T-Initiator. Contact angle measurements of 3T/3T-
Initiator film using (b) water (c) diiodomethane and
hexadecane.
114
Figure 4.4. XPS survey scan of 3T/3T-Initiator composite film. 115
Figure 4.5. SEM images of 3T film (with magnification of (a) ×73 (b)
×5000 (c) ×12000) and 3T/3T-Initiator (5 mM/5 mM)
composite film (with magnification of (d) ×73 (e) ×5000 (f)
×12000).
116
Figure 4.6. Static water contact angles of (a) 7.5/2.5 (b) 2.5/7.5 and (c)
0/10 mM 3T/3T-Initiator films. SEM images of (d) 7.5/2.5
(e) 2.5/7.5 and (f) 0/10 mM 3T/3T-Initiator, films at
×12000.
117
Figure 4.7. (a) Conditions for SI-ATRP of NIPAM from the
superhydrophobic and superoleophilic composite film. (b)
XPS survey scan after SI-ATRP of NIPAM. SEM images
after SI-ATRP of NIPAM at magnifications of (c) ×2000
and (d) ×10000.
120
Figure 4.8. (a) Side profile and (b) photographs of time dependent water
adsorption into 3T/3T-Initiator composite film after SI-
ATRP of NIPAM.
121
Figure 4.9. Contact angles of (a) water, (b) diiodomethane, (c)
hexadecane, (d) decline, (e) nitrobenzene, (f) and cooking
oil on 3T/3T-Initiator composite film after SI-ATRP of
HDFM.
124
Figure 5.1. (a) Structure of 2-(2,5-di(thiophen-2-yl)thiophen-3-yl)ethyl
2-bromo-2-methylpropanoate (3T-Initiator). (b) Static water
contact angle of 1:1 3T/3T-Initiator coated ITO. (c) Diagram
135
xxi
of electrodeposition conditions on ITO or steel substrates.
Figure 5.2. SEM images of 3T/3T-Initiator composite film on ITO
substrate at taken at magnifications of (a) ×73, (b) ×2000,
and (c) ×12000. (d) Line profile of stylus profilometry
measurements.
138
Figure 5.3. Structures of (a) 2-(2,5-di(thiophen-2-yl)thiophen-3-yl)ethyl
4-(benzodithioyl)-4-cyanopentanoate (3T-CTA), (b) prop-2-
ynyl 2-(2,5-di(thiophen-2-yl)thiophen-3-yl)acetate (3T-
Alkyne), (c) and (bicyclo[2.2.1]hept-5-en-2-yl)methyl 2-
(2,5-di(thiophen-2-yl)thiophen-3-yl)acetate (3T-Nb)
molecules. Static water contact angle of (d) 1:1 3T/3T-CTA,
(e) 1:1 3T/3T-Alkyne, (f) and 1:1 3T/3T-Nb coated ITO.
SEM images (magnification ×12000) of (g) 3T/3T-CTA, (h)
3T/3T-Alkyne, (i) and 3T/3T-Nb superhydrophobic
composite films.
140
Figure 5.4. (a) UV-Vis spectra of 3T/3T-Initiator composite film before
and after applying a potential of 1.05 V. (b) Static water
contact angles of undoped and doped 3T/3T-Initiator
composite film.
142
Figure 5.5. SEM images of doped 3T/3T-Initiator composite film on
ITO substrate taken at magnifications of (a) ×73, (b) ×2000,
and (c) ×12000. (d) Reversible static water contact angles of
the 3T/3T-Initiator composite film via potential switching
between 1.05 V (doping) and 0 V (dedoping).
144
Figure 5.6. Bacterial adhesion results after incubation for 2 h with B.
subtillis solution on different surfaces (1 mm2 x 1 mm
2):
Fluorescence images of (a) dedoped, (b) doped, and (c) bare
ITO 3T/3T-Initiator composite film. (d) Bar graph of the
statistical analysis of the bacterial cell adhesion on the three
surfaces. Notes: (1) * denotes results statistically significant
difference compared to the unmodified control (p < 0.05,
ANOVA on ranks). (2) ** denotes results statistically
significant difference compared to the doped surface (p <
0.05, ANOVA on ranks).
145
Figure 5.7. CV diagram of the electrodeposition of a 5 mM 3T and 5
mM 3T-Initiator solution onto a steel slide.
147
Figure 5.8. Static water and diiodomethane contact angles on the
3T/3T-Initiator composite film on a steel slide.
148
xxii
Figure 5.9. SEM images of 3T/3T-Initiator composite film coated on
steel slide.
149
Figure 5.10. (a) Digital photo images of the movement of a water droplet
on the superhydrophobic 3T/3T-Initiator composite steel
surface at sliding angle ≈ 0o. Digital photo images of (b)
static diiodomethane and hexadecane contact angles and (c)
the movement of a diiodomethane droplet on the
superoleophobic 3T/3T-Initiator composite steel surface at
sliding angle 3o ± 1.
150
Figure 5.11. Digital photo images of 3T/3T-Initiator composite coated
steel immersed in water taken from the (a) front and (b) the
side.
152
Figure 5.12. (a) Tafel and (b) Bode plots of bare steel, SH-steel, and
FSH-steel after being immersed in 0.5 M aqueous NaCl
electrolyte at pH 7 solution for 7 days.
155
Figure 6.1. Illustration of (a) polymer brush film fabrication (b) and
nanopatterning using current sensing AFM.
169
Figure 6.2. Cyclic voltamogram of electrodeposition of 3T-CTA. 173
Figure 6.3. (a) FT-IR spectra of electrodeposited 3T-CTA. (b) UV-vis
spectra of electrodeposited 3T-CTA and grafted 3T-
Methacrylate. AFM topography images of (c)
electrodeposited 3T-CTA (d) and grafted 3T-Methacrylate.
174
Figure 6.4. (a) Structure of 3T-CTA and demonstration of reactive sites.
(b) Mechanism of electropolymerization of 3T-CTA.
176
Figure 6.5. AFM topographic image of four lines pattern after (a)
applying -10 V at different writing speeds of 0.4, 0.6, 0.8,
and 1.0 μm/s (from left to right) (b) a constant writing speed
of 0.4 μm/s at different voltage bias ranging from -10,- 8,- 6
to -4 V. (c) Height profiles of four lines pattern after (c)
applying -10 V at different writing speeds of 0.4, 0.6, 0.8,
and 1.0 μm/s (from left to right) (d) a constant writing speed
of 0.4 μm/s at different voltage bias ranging from -10,- 8,- 6
to -4 V.
178
Figure 6.6. AFM current maps of four lines pattern after (a) applying -
10 V at different writing speeds of 0.4, 0.6, 0.8, and 1.0
179
xxiii
μm/s (from left to right) (b) a constant writing speed of 0.4
μm/s at different voltage bias ranging from -10,- 8,- 6 to -4
V. (c) Current profiles of four lines pattern after (c) applying
-10 V at different writing speeds of 0.4, 0.6, 0.8, and 1.0
μm/s (from left to right) (d) a constant writing speed of 0.4
μm/s at different voltage bias ranging from -10,- 8,- 6 to -4
V.
Figure 6.7. AFM (a) topography (b) and current map of a single line
created on electroactive film at -10 V at writing speed of 0.4
m/s. (c) I-V curves of different locations on the
electroactive material.
181
Figure 6.8. AFM images of (a-c) three squares and (d-f) the state of
Texas, where the images correspond to the AFM (a and d)
topography, (b and e) friction, and (c and f) current images.
183
xxiv
LIST OF SCHEMES
Scheme 1.1. Classical Formation Mechanism of Conducting Polymers
2
Scheme 1.2. General Mechanism of ATRP 10
Scheme 1.3. Chauvin Mechanism of Olefin Metathesis Reaction 12
Scheme 3.1. Polymerization of Styrene via (a) ATRP and Post
Nucleophilic Substitution, (b) and RAFT Polymerization
from 4-Cyano-4-(Thiobenzoylthio)Pentanoic Acid
82
Scheme 3.2. (a) Formation of Cbz-PPEGMEMA-CTA (b) and Thermo-
responsive Colloidal Cbz-PPEGMEMA-CTA Arrays
92
Scheme 4.1. Synthesis of 3T-Initiator 128
Scheme 5.1. Synthesis of 3T-Alkyne 158
Scheme AP.I.1. Synthesis of Cbz-OH
195
Scheme AP.I.2. Synthesis of Cbz-Initiator 199
Scheme AP.I.3. Synthesis of Cbz-CTA 200
Scheme AP.I.4. Synthesis of Cbz-Nb 202
Scheme AP.I.5. Synthesis of ATRP-Silane 202
Scheme AP.II.1. Synthesis of Cbz-TEG and Cbz-Alkyne 206
xxv
LIST OF ABBREVIATIONS
1-ODT 1-Octadecanethiol
AIBN 2,2’-Azoisobutyronitrile
2D Two-dimensional
3D Three-dimensional
ACN Acetonitrile
ATRP Atom transfer radical polymerization
AFM Atomic force microscopy
ATR-IR Attenuated total reflectance infrared spectroscopy
BE Binding energy
Bpy Bipyridine
b-NSA -naphthalene
Br Bromine
Cbz Carbazole
C Carbon
CTA Chain transfer agent
CRS Cold rolled steel
CP Conducting polymers
CPN Conjugated polymer networks
CA Contact angle
CuAAC Copper-catalyzed azide-alkyne cycloaddition
xxvi
CS-AFM Current-sensing atomic force microscopy
I-V Current-voltage
CV Cyclic voltammetry
DCM Dichloromethane
DCC Dicyclohexylcarbodiimide
DMAP Dimethylaminopyridine
DMF Dimethylformamide
E-DPN Electrochemical dip-pen nanolithography
EC-QCM Electrochemical quartz crystal microbalance
E-beam Electron beam
FHS-steel Fluorinated hydrophobic steel
FT-IR Fourier transform infrared spectroscopy
GPC Gel permeation chromatography
Au Gold
HDFM Heptadecafluorodecyl methacrylate
HTL Hole transport layer
ITO Indium tin oxide
LB Langmuir Blodgett
LBL Layer-by-layer
MBMP Methyl 2-bromo-2-methylpropionate
Methyl methacryalte
MeOH Methanol
xxvii
CP Microcontact printing
Mn Molecular weight
MIP Molecularly imprinted polymers
Mo Molybdenum
NIPAM N-isopropylacrylamide
N Nitrogen
NMP Nitroxide mediated polymerization
PMDETA N,N,N′,N′′,N′′-pentamethyldiethylenetriamine
Nb Norbornene
NMR Nuclear magnetic resonance
OEG Oligo(ethylene glycol)
OLED Organic light emitting diode
OPV Organic photovoltaic device
O Oxygen
PDI Polydispersity index
PFOSA Perfluoroctane sulfonic acid
PEDOT Poly(2,4,-ethylenedioxythiophene)
Pt Platinum
PANI Polyaniline
PDMS Polydimethylsiloxane
PDI Polydispersity index
PPEGMEMA Poly(poly ethylene glycol methyl ether methacrylate)
xxviii
PMMA Poly(methyl methacrylate)
PDMAM Poly(N,N dimethylacrylamide)
PS Polystyrene
PSS Poly(styrene sulfonate)
PVK Poly(vinyl carbazole)
RAFT Reversible-addition fragmentation chain transfer
ROMP Ring opening metathesis polymerization
Ru Ruthenium
W Tungsten
SAM Self assembled monolayer
SECM Scanning electrochemical microscopy
SEM Scanning electron microscopy
SDS Sodium n-dodecyl sulfate
CAdiiodo Static diiodomethane contact angle
CAhexadec Static hexadecane contact angle
CAoil Static oil contact angle
CAwater Static water contact angle
S Sulfur
SEE Superhydrophobic electroactive coating
SH-steel Superhydrophobic steel slide
SI Surface initiated
SI-ATRP Surface initiated atom transfer radical polymerization
xxix
SIP Surface initiated polymerization
SI-RAFT Surface initiated reversible-addition fragmentation chain
transfer
SI-ROMP Surface initiated ring-opening metathesis polymerization.
3T Terthiophene
TBAH Tetrabutylammonium hexafluorophosphate
TEG Tetraethylene glycol
THF Tetrahydrofuran
TEA Triethylamine
UME Ultramicroelectrode
XPS X-Ray photoelectron spectroscopy
1
Chapter 1. Introduction
Interest in polymer as conducting materials began in late the 1970’s when Heeger,
MacDiarmid, and Shirakawa discovered that once doped, polyacetylene exhibited metal-
like conductivity.1 This high conductivity (near silver) sparked research efforts to develop
applications such as organic light-emitting diodes (OLED’s), sensors, storage devices,
surface functionalization, surface patterning, and organic photovoltaic devices (OPV’s).2
Due to these applications, numerous organic conducting polymers have been synthesized
that incorporate novel functional groups in order to obtain the above mentioned
applications.3 To date, many derivatized electroactive monomers and precursor polymers
have been reported that form conjugated polymer network (CPN) films.4 This chapter
introduces recent efforts on these materials and their applications on surfaces and
interfaces, including patterning. The synthesis methods and fabrication protocols
encountered in the course of the dissertation are also discussed. Nature-inspired
morphologies may also yet influence specific nanostructuring protocols towards new
applications. The specific objectives of each part of this dissertation are then presented at
the end of this chapter.
2
1.1. General Principles of Electropolymerization
1.1.1. Mechanisms
The mechanism of electropolymerization of conducting polymers has been well-
investigated. Diaz and coworkers were the first to present mechanistic studies for the
formation of conducting polymers.5-6
Diaz suggested, that the polymerization of pyrrole
monomers involves dimerization after oxidation, and proton elimination occurs from the
doubly charged dimer, forming an aromatic neutral dimer. Since the dimer has greater -
conjugation or delocalization, oxidation to form the cation occurs more easily in
comparison to the monomer. The cation then undergoes a coupling step with a
monomeric radical cation, and from the resulting charged trimer, proton elimination
occurs restoring aromaticity (Scheme 1.1). This mechanism, is widely accepted in the
literature.7
Scheme 1.1. Classical Formation Mechanism of Conducting Polymers
NH
NH
NH
+NH
NH
NH
NH
-2e -2H+
NH
NH
HN
n+
NH
+-2H+
k
NH
NH
HN
(n-1)+k
HN
3
Similarly, Savéant et al. investigated the formation of intermediates. These results
showed that radical cations of the electroactive monomers and the oligomeric
intermediates are involved in the oligomerization reaction.8 Studies by Heinze et al. on
substituted thiophenes confirm these findings.9 Heinze also showed that the consecutive
oligomerization begins in solution and takes place via successive dimerization steps, from
a dimer to a tetramer to an octameric product.9 Lukkari et al. also showed that initially
oligomers are formed in solution, and that the electrodeposition of the electroactive
oligomers depends on the properties of the electrode, e.g. indium tin oxide (ITO),
platinum (Pt), or gold (Au) surfaces.10
1.1.2. Electro-grafting
The term electro-grafting has been used to characterize an electrochemical
reaction where an organic material binds to an electrode i.e. a conducting substrate. As
described earlier, polymerization starts with the formation of oligomers in solution. The
next general step is the deposition onto a conducting surface or electrode. This step
involves nucleation, growth, and additional chemical reactions under solid state
conditions.11
Potentiostatic, and potentiodynamic techniques can be used to create and
examine the electro-grafting process. As an example, potentiodynamic (cyclic
voltammetry (CV)) experiments provide information on the growth rate of conducting
polymers. The increase in current with each cycle of a potentiodynamic diagram is
directly proportional to the increase in the amount of rechargeable redox sites on a
surface.12
Further evidence of successful electro-grafting comes from mass changes
4
during the electrodeposition process. For example, the mass changes can be monitored
using electrochemical quartz crystal microbalance measurements (EC-QCM), where
potential step techniques and CV have been coupled to the QCM technique.13
Electro-grafting adds to the other well studied methods for surface modification
such as silanization and phosphonatation of oxidized surfaces, and self-assembly of thiols
on Au surfaces and surfaces of other metals. It should be mentioned however that silanes
and thiols require specific surfaces in order to adsorb. In the case of electroactive
monomers, many types of conducting or electrode surfaces (metals, carbon, metal oxides,
etc.) can be coated via electrochemical means giving a great advantage to the method.
Similarly, electro-grafting also allows for large surface areas to be coated with an
electroactive monomer.
1.2. Electro-grafting of Polymerizable Electroactive Monomers and Polymer
Brushes
Another valuable property of organic electroactive monomers is that they can be
synthesized to incorporate a variety of functional groups. One area of recent interest is
the ability to perform surface initiated polymerization (SIP) to form polymer brushes
using a variety of different polymerizable functional groups tethered to a surface.
Polymer brushes are polymer coatings consisting of polymeric chains that are end-
tethered to an interface. At high grafting densities, steric repulsion leads to stretching and
brush conformations.14
5
Polymer brushes can be prepared by either the “grafting to” or the “grafting from”
strategies. In the case of the “grafting to” approach the tethering of prefabricated
polymers can be done using covalent bond formation i.e. chemisorption (Figure 1.1).15
Although experimentally facile, the “grafting to” approach has several limitations. These
limitations include difficulty in producing thick and dense polymer brushes, the
formation is hindered by steric repulsion between polymer chains16
Figure 1.1. Synthetic strategies for the preparation of polymer brushes via chemisorption
reaction of end-functionalized polymers with complementary functional groups at the
substrate surface.
In the “grafting from” approach (Figure 1.2), the polymerization is directly
initiated from functionalized surfaces.17
Controlled polymerization techniques are of
interest in controlling the thickness, composition, and architecture of polymer brushes.18
Most of the polymer brushes produced by the “grafting from” approach use surface-
initiated (SI) controlled radical polymerization techniques.
6
Figure 1.2. Synthetic strategies for the preparation of polymer brushes grown via SIP
technique.
1.2.1. Reversible-Addition Chain Transfer Radical Polymerization
Reversible-addition fragmentation chain transfer (RAFT) polymerization is based
on reversible chain transfer and has been used to prepare polymer brushes via SIP or SI-
RAFT.19
An early example of SI-RAFT polymerization was reported by Baum et al. ,
who prepared poly(methyl methacrylate) (PMMA), polystyrene (PS), and poly(N,N
dimethylacrylamide) (PDMAM) brushes from azo-functionalized surfaces in the presence
of the chain transfer agent (CTA) 2-phenylprop-2-yl dithiobenzoate and free initiator
(2,2′-azoisobutyronitrile (AIBN)).20
The purpose of a free initiator is to facilitate polymer
brush growth by increasing the concentration of radicals in the system.21
Based on the above interest in SI-RAFT, researchers have now applied
functionalizing conductive surfaces with electro-grafted materials containing RAFT-
CTA’s in order to perform SI-RAFT. For example, the synthesis of grafted homopolymer
and block copolymer films were reported using an electro-grafted polyterthiophene on an
ITO and Au electrode containing a RAFT-CTA moiety (Figure 1.3).22
Diblock
7
copolymer brush formation revealed capabilities of a conventional SI-RAFT procedure
using the polyterthiophene macroinitiator film.
Figure 1.3. General route for preparing polymer brushes from an electro-grafted
terthiophene CTA.
Similarly, Tria et al. introduced a novel and versatile method of grafting protein
and cell-resistant poly(poly ethylene glycol methyl ether methacrylate) (PPEGMEMA)
brushes on conducting Au surface.23
The process started with the electrochemical
8
deposition of an electro-active CTA onto an Au electrode (Figure 1.4). The capability of
the electrodeposited CTA to allow for SI-RAFT polymerization of PPEGMEMA brushes
was demonstrated by the increase in thicknesses of the films after polymerization. The
ability of the PPEGMEMA-modified Au surface to resist nonspecific adhesion of
proteins and cells was monitored and confirmed by XPS, ellipsometry, contact angle, and
fluorescence imaging. This method shows that electro-grafted materials can serve as a
robust protein and cell-resistant coatings for electrically conducting biomedical devices.
Figure 1.4. General outline for the preparation of protein and cell-resistant PPEGMEMA
brushes from the electrodeposited RAFT agent.23
9
Tria and coworkers have also shown that electrochemically cross-linked surface-
grafted poly(N-vinylcarbazole) (PVK) brushes can serve as hole transport layers (HTLs)
for photovoltaic device applications using SI-RAFT polymerization from electro-grafted
initiators.24
Here they found that comparable performance to poly(3,4-ethylene
dioxythiophene):poly(styrene sulfonate) PEDOT:PSS based devices could be achieved.
The main advantage of the electro-grafted material is the strong adhesion to ITO possibly
allowing long-term stability against acid dopants and oxygen.24
Analogous to the above examples, direct electro-grafting of a series of well-
defined dendritic linear polymers via the RAFT polymerization technique has also been
done. For example, Patton et al. used dendritic CTAs possessing a single dithioester
moiety at the focal point, where RAFT polymerization could be carried out.25
This was
done in order to attach PS and PMMA chains of controlled lengths to an ITO or Au
electrode. To provide electrochemical functionality, the dendritic CTAs were designed
with carbazole moieties at the periphery of the structures. Although this method did not
use incorporated functional groups after electro-grafting the living polymerization
characteristics of RAFT does theoretically allow for further polymerizations from the
surface.
1.2.2. Atom Transfer Radical Polymerization
Another type of polymerization technique that has been used to produce polymer
brushes is atom transfer radical polymerization (ATRP). Compared to other controlled
radical polymerization techniques, ATRP is extremely robust.26
The process of ATRP
10
relies on the “reversible redox activation of a dormant alkyl halide terminated polymer
chain end by a halogen transfer to a transition metal complex”.26
The formal homolytic
cleavage of the carbon-halogen bond, creates a free and active carbon radical at the
polymer chain end (Scheme 1.2). This step is based on a single electron transfer from the
transition metal complex to the halogen atom, leading to the oxidation of the transition
metal complex.26
Scheme 1.2. General Mechanism of ATRP
R-X + Mnt -Y / Ligand
kact
kdeact
R
kp
monomer
+ X-Mtn+1-Y / Ligand
kt
termination
SI-ATRP was first reported by Huang and coworkers who grafted polyacrylamide
brushes from halogenated terminated initiators attached to silica particles.27
This SI-
ATRP has also been successfully used by Sedjo et al. to prepare PS brushes from a
functionalized silica substrate using Cu(II)Br2/bipyridine (bpy) agent.28-29
Like SI-RAFT polymerization from electro-grafted films, SI-ATRP has also been
performed from similar materials. For example, Matrab et al. reported on the preparation
of PMMA, poly(n-butyl acrylate), and PS brushes at the surface of steel electrodes that
were modified by the electrochemical reduction of a brominated aryl diazonium salt.30
Similarly, SI-ATRP from electro-grafted materials has also been performed.31
For
example, they electrodeposited electroactive materials with ATRP containing groups on
11
PS colloidally templated ITO electrodes (colloidal templating will be described in depth
in subsequent sections). In this work the PS served as a sacrificial template, from which
once removed, a hexagonally closed packed array of the polymer network of ATRP
macroinitiator was observed. Due to the ATRP moiety, SI-ATRP of MMA was
achieved.
Although fewer reports have been published using SI-ATRP from electro-grafted
materials, the ease and versatility of ATRP (i.e. cheap starting materials and little needs
to be done to isolate reaction from the atmosphere) make it an attractive alternative
compared to the SI-RAFT polymerization.
1.2.3. Ring-opening Metathesis Polymerization
Ring-opening metathesis polymerization (ROMP) constitutes an important class
of organometallic transformation reactions which results in polymerization of olefins in
the presence of metal carbine complexes. The first mechanistic insight into olefin
metathesis came from Chauvin and Hérisson who proposed the [2+2] cycloaddition and
the following cycloreversion to an olefin (Scheme 1.3).32
Initially, the catalysts for olefin metathesis were based on heterogeneous or
homogeneous early transition metal carbine complexes. Over the past several decades,
efforts have been focused on developing new metal catalysts i.e. tungsten (W)- and
molybdenum (Mo)- based transition metal catalysts.33
Catalysts based on late transition
metals i.e. ruthenium (Ru) have shown great promise in initiating living ROMP in the
12
Scheme 1.3. Chauvin Mechanism of Olefin Metathesis Reaction
R1
R2 R3
MR1
R2 R3
MR2
+
R1
R3
presence of a variety of functional groups.34
For this reason, Grubb’s first (1) and second
(2) generation catalysts have been of profound interest to both industry and academia
(Figure 1.5).34
Due to these developments ROMP has emerged as a powerful technique
for preparing materials with a wide range of applications.35
As a living/controlled
polymerization technique, ROMP is a capable of synthesizing macromolecules with
controlled polymer chain lengths and narrow polydispersity index (PDI). Mechanically,
ROMP is a chain growth polymerization were the cyclic olefin monomers’ carbon-carbon
double bonds exchange, mediated by the metal catalysts. The driving force behind ROMP
is the release of the ring strain of cyclic alkenes from monomers to polymers. The whole
process is equilibrium controlled and completely reversible, according to Chauvin’s
proposal.
Ru
PCy3
PCy3
Ph
Cl
Cl Ru
PCy3
Ph
Cl
Cl
NN
Grubbs' first generation catalyst Grubbs' second generation catalyst
(1) (2)
Figure 1.5. Grubbs’ first and second generation catalyst 1 and 2 (Cy = cyclohexyl).
13
There have also been recent developments in SI-metathesis polymerization and its
applications.36
For example, Jiang et al. used terthiophene derivatives molecules to
electrochemically functionalize a conducting surface, with peripheral olefins (Figure
1.6). From the terminal olefins SI-metathesis polymerization was used to form grafted
polynorbornene brushes.37
Figure 1.6. Polynorbornene brushes synthesized via Surface Initiated – Ring Opening
Metathesis Polymerization (SI-ROMP). Adapted with permission from ref 37. Copyright
2010 American Chemical Society.
1.2.4. Click Chemistry
The click concept was first reported in 2001 by Barry Sharpless and co-workers.38
The required characteristics for a click reaction generally include mild reaction
conditions, readily available starting materials, the ability to run the reactions in a benign
14
easily removed solvent, and orthogonal (i.e. highly specific and regioselective) reaction
routes. If purification is required then it must be by non-chromatographic methods.38
An
important finding in terms of the development of the click concept came with the
discovery that Cu(I) promotes the rate of the Huisgen 1,3-dipolar cycloaddition as well as
providing regiospecificity with the generation of the 1,4-triazole isomer.39,40
These
reports were followed by the studies of Fokin et al. , in which they reported that the
azide–alkyne coupling reaction, when carried out in an aqueous phase in the presence of
copper sulfate and sodium ascorbate, is highly regiospecific.41
Since then click chemistry
has found numerous applications in various fields, i.e. drug discovery, material
fabrication, and synthesis.42
Common examples of click reactions are cycloaddition reactions of unsaturated
species (Diels–Alder cycloadditions), nucleophilic substitution chemistry, (ring-opening
reactions of strained heterocycles such as epoxides), carbonyl chemistry of the ‘‘non-
aldol’’ type, and carbon–carbon multiple bond addition, especially oxidative i.e.
epoxidation, dihydroxylation, aziridination, and sulfenyl halide additions.38,43-46
The most
popular example of click chemistry is the copper-catalyzed Huisgen 1,3-dipolar
cycloaddition of azides and terminal alkynes (yields are often above 95%). Moreover, the
copper-catalyzed azide–alkyne cycloaddition (CuAAC) reaction can be performed in
various solvents and in the presence of numerous other functional groups. Click
chemistry has also been used to functionalize surfaces. For surface modification, the
Cu(I) catalyzed Huisgen 1,3-dipolar cycloaddition of alkynes and azides in particular, are
15
of great significance because they serve as efficient coupling reactions on solid surfaces,
which allow for the creation of complex architectures.47
Among its many uses, click chemistry has been found to be extraordinarily useful
in electrode plating. For example, Kiskan et al. reported a method for the preparation of
polymers with the azide and alkyne groups serving as reactive sites for the covalent
binding of pyrrole and thiophene to the functional side chains via click chemistry (Figure
1.7).48
In their work, they independently prepared propargyl functional pyrrole and
thiophene that were coupled with azido PS (PS-pyrrole and PS-thiophene) in the presence
of Cu(I)Br/bpy ligand at room temperature with high efficiency.48
The obtained polymers
were structurally and electrochemically characterized and ultimately deposited onto
platinum electrodes. This work was the first report on click chemistry as a route to
covalently bind electro-active groups into conventional polymers.
N3
n m
N
O
S
OO
N
n m
N
n m
N N
N N
OO
S
ON
+
CuBr, bpy
THF, 25 oC
24 h
CuBr, bpy
THF, 25 oC
24 h
PS-thiophene
PS-pyrrole
Figure 1.7. Synthesis of PS- pyrrole and PS-thiophene by click reaction
16
Similarly Kunz and coworker, electro-grafted poly-3 and poly-1 (Figure 1.8) onto
electrode surfaces such as carbon.49
Deposition of polymers having known structures
onto electrode surfaces provided a direct correlation between the structure–property
relationships observed for the surface-bound species. This understanding may help
improve synthetic strategies towards the desired electrochemical properties of such
conjugated organic materials.50
S S
N3
C6H13
x y
+
N
O
O
S S
N
C6H13
x y
NN
O
NO
poly-1
poly-3
CHCl3/DMF
25 mol% CuI
Figure 1.8. Structure of poly-1 and synthesis of poly-3.
Grafting of electroactive materials to already functionalized surfaces has also
gained interest. For example, Collman and Hosseini, showed that “click” chemistry
applied to azide terminated SAMs offers an easy and convenient method to modify
electrode surfaces with ferrocene.51
Click chemistry provided a robust and efficient
method to bind electroactive ferrocene molecules. Knowledge gained on the physical
parameters that affect electron transfer to redox molecules such as biomimetic
environments, is of importance in understanding redox proteins.51
Similarly, these
17
methods provide a useful platform for future study of multi-electron, multicatalytic
processes involving the generation or consumption of highly reactive species.51
1.3. Surface Patterning
The ability to pattern surfaces on the micro- and nanoscale is the basis for a wide
range of applications including microelectronics, photonic structures, microfluidics,
biosensors, and surface science.2 Examples of patterning techniques are
photolithographic process. microcontact printing (CP), electron-beam (e-beam)
lithography, and scanning probe lithography.52,53
Sections 1.3.1 and 1.3.2 will specifically
discuss template surface patterning techniques aided by electro-active materials i.e.
colloidal templating and scanning probe lithography techniques.
1.3.1. Colloidal Templating
Electropolymerization in hard or sacrificial templates provides a straightforward
way to produce specific shapes of conducting polymers on the micro and nanometer
scale. Templated electro-grafting can be performed within porous template via channels,
holes, or cavities as long as it has a continuous opening to the underlying electrode,
where the dimensions of the template determine the size of the electro-grafted material.54
It is well-known that colloids made out of SiO2 or polystyrene (PS) can self-
assemble into periodic three-dimensional structures.55
Electro-grafting onto colloidally
templated surfaces consists of three steps (Figure 1.9a). First an ordered PS colloidal
crystal is deposited onto an electrode (Figure 1.9b). Then a monomer/electrolyte is
18
electro-grafted into the interstitial spaces of the colloids. Lastly when the sacrificial
template is removed (in the case of PS), a microporous structure of the electro-grafted
material with inverse opal morphology is created. An example of this methodology was
demonstrated by Knoll et al. , who used colloidal templating to fabricate ordered
honeycomb shaped polyaniline (PANI) and its copolymers with poly(acrylic acid) and
poly(styrene sulfonate) (Figure 1.9c and d).56
Figure 1.9. (a) Schematic illustration of the procedure used for fabricating PANI inverse
opal microstructures via electropolymerization within a PS colloidal crystal on top of a
gold electrode. SEM-images of the (b) colloidally templated gold surface and (c and d)
PANI inverse opals with two different magnifications. Reprinted with permission from
ref 56. Copyright 2005 American Chemical Society.
The inverse opal PANI films exhibited high quality patterns and remained
electroactive in buffer solutions at neutral pH, making these films good candidates for
biosensing applications.56
For example, polypyrrole-based inverse opals have been used
19
as transducers for biosensors upon charging the conducting polymer matrix with an
enzyme.57
These results were explained by an increase in the electroactive area.58
Similarly, Pernites et al. used molecularly imprinted polymers (MIP) in combination
with colloidal templating for chiral sensing applications (Figure 1.10).59
Here an electro-
grafted polyterthiophene MIP film was fabricated for the sensing of a chiral compound
and prohibited drug (−)-norephedrine (1R, 2S) over its diastereomer (+)-norephedrine
(1S, 2S).59
The new assembly of electropolymerized MIP film demonstrated a much
higher sensing response when templated than the conventional flat MIP film.
Figure 1.10. AFM 2D topography images (3D inset) of the (a) PS-coated substrate and
(b) molecularly imprinted and templated surface before norephedrine removal. Reprinted
with permission from ref 59. Copyright 2012 Wiley.
Back filling of colloidally templated surfaces has also been performed. For
example, Pernites and coworkers demonstrated a simple approach to fabricate a binary
20
composition of highly ordered 2-D conducting polymer pores by template directed
electro-grafting followed by SAM formation of 1-octadecanethiol (1-ODT).60
The
backfilling of the inside cavities by the SAM approach resulted in a 2-D binary patterned
Figure 1.11. AFM topography images (3D inset) of a 500-nm backfilled templated array
((a) 5 μm X 5 μm and (b) 2 μm X 2 μm scans), along with (c) line profile analysis before
and after backfilling with 1-ODT. (d) High resolution XPS scan of S 2p peak. . Reprinted
with permission from ref 61. Copyright 2011 American Chemical Society.
chemistry.60
Changes in the surface morphology depicted by AFM images (Figures
1.11a and 1.11b) confirm the backfilling of the cavities. Further evidence of success
comes from the AFM line profile which shows a change in the peak-to-baseline height
profile after back filling with 1-ODT (Figure 1.11c) and from the high resolution XPS
21
scan of the S 2p peak (Figure 1.11d). Thus, this procedure provides another route for the
fabrication of binary patterned surfaces. Binary patterned surfaces usually require more
complicated or expensive lithographic methods.61
It also follows that other thiols or
another conducting polymer can be used for backfilling purposes. In fact, the availability
of the unmodified Au surface should make it amenable for other Au surface chemistries,
including metal deposition and polymer brush synthesis. Similarly, SI-ATRP from SAM
of ATRP initiators from colloidally templated surfaces has also been performed.62
For
example, the Advincula research group performed SI-ATRP of N-isopropylacrylamide
(NIPAM) from an ATRP initiator SAM deposited into the cavity of a colloidally
templated ITO and Au substrate.
Other types of SIP techniques have also been performed from the hexagonally
closed pack arrays formed from electro-grafted initiators on a colloidally templated
surface. For example, our group has recently reported SI-ATRP, -RAFT polymerization,
and -ROMP from colloidally templated electroactive initiators, i.e. 3,5-bis(4-(9H-
carbazol-9-yl)butoxy)benzyl 2-bromo-2-methylpropanoate (Cbz-initiator), 3,5-bis (4-
(9H-carbazol-9-yl) butoxy) benzyl 4-cyano-4 (phenylcarbonothioylthio) pentanoate (Cbz-
CTA), and Bicyclo[2.2.1]hept-5-en-2-ylmethyl 3,5-Bis-(4-(9H-carbazol-9-yl) butoxy)
benzoate (Cbz-Nb) (Figure 1.12a-c). The built-in ATRP, RAFT, or ROMP moiety
allowed for the formation of patterned polymer brush systems via SIP of methyl
methacrylate, styrene, or norbornene monomers from the inverse colloidal Cbz-Intiator, -
CTA, -Nb arrays respectively.
22
Figure 1.12. Structures of (a) 3,5-bis(4-(9H-carbazol-9-yl)butoxy)benzyl 2-bromo-2-
methylpropanoate (Cbz-Initiator), (b) 3,5-bis (4-(9H-carbazol-9-yl) butoxy) benzyl 4-
cyano-4 (phenylcarbonothioylthio) pentanoate (Cbz-CTA), and (c) Bicyclo[2.2.1]hept-5-
en-2-ylmethyl 3,5-Bis- (4-(9H-carbazol-9-yl) butoxy) benzoate (Cbz-Nb). Structures of
(d) prop-2-ynyl 3,5-bis(4-(9H-carbazol-9-yl)butoxy)benzoate (Cbz-alkyne), (e) 2-(2-(2
(2-hydroxy)ethoxy)ethoxy)ethyl-3(4-(9H-carbazol-9-yl)butoxy)-5-(4-(9Hcarbazol-
9yl)butoxy)) benzoate (Cbz-TEG), (f) electroactive dendritic-linear PPEGMEMA (Cbz-
PPEGMEMA-CTA) molecule, (g) linear PS with terminal azide functional group (PS-N3)
and, (h) linear PS with terminal alkyne functional group (PS-alkyne).
The “grafting to” approach has also been performed on colloidally templated
surfaces as an example, the electrodeposition of a series of first-generation dendrons
23
(Figure 1.12d-f) onto colloidally templated substrates has been reported.63
The first part
of the paper focused on the grafting of linear polystyrene molecules (Figure 1.12g and
h) containing either an azide (PS-N3) or terminal alkyne (PS-alkyne) via the CuAAC
reaction onto colloidally templated conducting polymer arrays. Figure 1.13 demonstrates
how the successful grafting of the PS-N3 (Figure 1.13, Route 1) or PS-alkyne (Figure
1.13, Route 2) was achieved either through the use of the electroactive
Figure 1.13. Fabrication of a highly ordered monolayer of colloidal arrays (500 nm
diameter PS microspheres), inverse colloidal arrays, and patterned polymer brushes via
the “grafting to” approach using linear (Route 1) PS-N3, (Route 2) PS-alkyne or, (Route
3) Cbz-PPEGMEMA-CTA polymers.
24
“clickable” molecule prop-2-ynyl 3,5-bis(4-(9H-carbazol-9-yl)butoxy)benzoate (Cbz-
alkyne), or by backfilling an inverse colloidal 2-(2-(2-(2-hydroxy)ethoxy)ethoxy)ethyl-
3(4-(9H-carbazol-9-yl)butoxy)-5-(4-(9Hcarbazol-9yl)butoxy)) benzoate (Cbz-TEG) array
with azidoundecanethiol SAM, respectively. The second part of the paper examined an
alternative route (Figure 1.13, Route 3) for the direct grafting of electroactive linear
polymers via electrodeposition onto colloidally templated surfaces. This was achieved by
first polymerizing a linear poly((polyethylene glycol)3 methyl ether methacrylate)
(PPEGMEMA) from an electroactive RAFT polymerizable reagent i.e. 3,5-bis (4-(9H-
carbazol-9-yl) butoxy) benzyl 4-cyano-4 (phenylcarbonothioylthio) pentanoate (Cbz-
CTA). Following the electrodeposition of the electroactive linear PPEGMEMA (Cbz-
PPEGMEMA-CTA) and removal of the PS microspheres, novel temperature responsive
tuning of pore diameter was achieved.
1.4.2. Patterning with Scanning Probe Techniques
Direct writing of micro- and nanostructures with high resolution can be achieved
with scanning probe techniques. Scanning electrochemical microscopy (SECM) is a
surface analysis and modification technique in which an ultramicroelectrode (UME) is
scanned along a conductive surface immersed into an electroactive monomer/electrolyte
solution.2 Scanning the ultramicroelectrode (UME) at a constant height provides valuable
information about local surface conductivity, morphology, concentration profiles, and
maps of reactive sites.2 The first experiments on the deposition of conducting polymers
25
with SECM were performed in the direct mode where the substrate served as counter
electrode.64,65
Nanostructures in the subnanometer scale can also be fabricated using
electrochemical dip-pen nanolithography (E-DPN) which is an AFM lithography
technique using a conducting AFM tip.66
E-DPN works by first immersing the
conducting AFM tip into a solution of electroactive monomer. Then, when the AFM tip is
in contact with the surface, spontaneous condensation facilitates the transport of material
from the AFM tip to the surface, and an electrochemical reaction can then immobilize the
material on the surface. Material deposition is localized on the patterns traced by the
AFM tip, providing a site-specific technique. In the experiments by Liu et al., a typical
experiment first involved the coating of a doped silicon AFM tip by soaking it in an
ethylenedioxythiophene (EDOT) solution.67
Upon application of a negative bias between
the AFM tip and the surface, EDOT is electropolymerized, leading to a tip-defined
electrodeposition of the conjugated polymer.67
The formation of nanowires can also be initiated from a direct-writing process
after an electroactive material has been coated onto an electrode using current sensing
AFM (CS-AFM). Recently, electroactive precursor polymer films have been fabricated
using spincoating, Langmuir-Blodgett (LB) techniques, and layer-by-layer (LBL).68
These films served as precursors towards the fabrication of conjugated polymer
nanopatterns. These methods allow for control over the spatial and electrical properties of
the resulting nanostructures based on bias voltage and writing speed. For example, Huang
26
and coworkers first fabricated ultrathin films of pendant carbazole-modified
polyelectrolytes using the LBL deposition technique. Due to the electroactive pendant
carbazole units on the polymer backbone highly ordered nanostructures/patterns were
created using CS-AFM.68d
For example, as seen in the AFM topography (Figure 1.14a)
and current mapping images (Figure 1.14b) well-defined nanopatterns (nanocar) were
fabricated by electrochemically cross-linking the pendant carbazoles.
Figure 1.14. CS-AFM nanopatterning of a “nanocar” on a 10-bilayer P4VPCBZ/PAA
film at 10 V with a writing speed 0.8 µm/s (a) topographic image and (b) current image.
The current image was obtained by scanning at 1 V after the patterning. Color bar range
is 0−14.7 pA. Reprinted with permission from ref 68d. Copyright 2008 American
Chemical Society.
1.4. Electroactive Materials as Viable Coatings for Anti-wetting Characteristics
Superhydrophobic surfaces have vital importance in naturally occurring systems.
A surface is said to be superhydrophobic when the water droplet on the surfaces has a
contact angle (CA) greater than 150o.69
Superhydrophobic coatings are nature inspired,
with the lotus leaf (Figure 1.15a and b), the butterfly wing (Figure 1.15c), and the water
strider (Figure 1.15d), being the classic examples.69-71
Surface texture, or roughness, is
27
typically used to enhance the hydrophobic nature of the surface. The high water
repellence of superhydrophobic surfaces make them ideal candidates for industrial
applications including self-cleaning, biocorrosion inhibitors, antifouling marine coatings,
microfluidics, and anti-ice adhesion systems.71
These properties have inspired research
developments for the establishment of methodologies and theoretical modeling of how to
obtain superhydrophobic surfaces.
Figure 1.15. Photographs of the (a and b) of the lotus leaf, (c) butterfly, (d) and water
strider.
Two such models based on the works of Wenzel and Cassie-Baxter are often used
to predict CAs on rough surfaces.70
Wenzel suggested that if liquid contact followed the
contours of a rough surface then the effect of roughness should be to emphasize the
28
intrinsic wetting tendency towards either film formation or enhanced contact angle. The
contact angle observed on this type of surface is given by Wenzel’s equation,
cos(= rcos() (1)
where the roughness factor r is the ratio of the true surface area of the solid to its
horizontal projection and is the equilibrium contact angle on a smooth flat surface of
the same material.70
The contribution from the roughness is contained within r and the
effect of surface chemistry is contained in (Figure 1.16a). However, it can be
energetically favorable for a liquid to bridge across the tops of surface features so that the
Figure 1.16. Wetting states (a) Wenzel, (b) Cassie–Baxter.
droplet rests upon a composite surface of flat solid tops and flat air gaps between them, as
described by the Cassie–Baxter relationship, (Figure 1.16b). The contact angle is then
given by a weighted average of the cosines of the contact angles on the solid and air
interfaces using,
cos(*) = (cos()) (1 cos(x) (2)
29
where is the fraction of the surface present at the tops of the surface protrusions, and
(1 is the fraction that corresponds to the air gaps, x is the contact angle on the gas in
the gaps which is taken to be 180o
1.4.1. Templating Approach
Because of the interest in superhydrophobic coatings a large number of different
methods have been used to fabricate these types of surfaces. Examples include the use of
nanoparticles, chemical etching, micro-structuring, electrospinning, and LBL assemblies.
Although these methods provide sufficient means to create superhydrophobic surfaces, in
most cases they require lengthy or complicated steps or require expensive and
sophisticated equipment. Another means of fabricating superhydrophobic surfaces is to
use template assisted methods combined with hydrophobic electroactive materials. For
example, gold, ITO, or steel surfaces have been made to be superhydrophobic (Figure
1.17a) and superoleophilic (Figure 1.17b and c) by first applying a monolayer of PS
colloids (colloidal templating) onto the respective surfaces.76
After the formation of the
monolayer of PS colloids, a terthiophene ester derivate was electro-grafted on top of the
monolayer. The fabricated nanostructured surface exhibited unique dual wetting
properties (Figure 1.17d and e) i.e. superhydrophobic and superoleophilic (CAoils ≈ 0o).
These coatings may prove useful in the selective removal of oil and organic solvents
during water recycling.76
They may also find many practical applications as coatings for
anti-ice adhesion, marine coatings, anticorrosion, and stimuli-responsive surfaces such as
intelligent microfluidic switches.
30
Figure 1.17. Contact angle measurements of poly(3T-COOR) onto 500 nm PS/Au in (a)
water, (b) diiodomethane, and (c) hexadecane. (d) Low 24 μm × 36 μm and (e) high
magnification SEM images of poly(3T-COOR) onto 500 nm PS/Au at 4 μm × 3 μm.
Reprinted with permission from ref 76a. Copyright 2012 Wiley.
Similarly, the selective prevention or adhesion of proteins and bacteria has been
also demonstrated on a self-cleaning superhydrophobic colloidally templated
polyterthiophene derivative.77
Here the fabricated colloidally templated electro-grafted
polymeric surface proved to be highly stable and non-wetting over a wide range of pH
(pH 1-13) and temperature (between 4 and 80 oC). Furthermore, the superhydrophobic
surface demonstrated self-cleaning effects at a sliding angle of ~ 3o. Another interesting
facet of electro-grafted superhydrophobic coatings is that by simply manipulating the
31
redox properties of the conducting polymer with a constant potential, the wettability of
the surface can be changed from superhydrophobic to hydrophilic (CAwater ≈ 60o). Since
the switching of the surface wettability can be easily achieved, the electro-grafted
coatings maybe useful for fabricating smart coatings, which can be tuned to resist or
adsorb protein and bacterial cell.76a
Figure 1.18. (a) Photograph of the Xanthosoma Sagittifolium leaves. (b) SEM image of
the leaf. (c) SEM images of the imprinted layers of SEE showing a top view of the
surface. (d) SEM images of the imprinted layers of SEE showing a cross-section view of
the surface. Reprinted with permission from ref 78. Copyright 2011 American Chemical
Society.
Superhydrophobic surfaces have also been prepared usingCP. For example,
Weng et al. created novel anticorrosion coating materials by first molding a Xanthosoma
sagittifolium leaf (Figure 1.18a and b) using polydimethylsiloxane (PDMS).78
32
Subsequently, the superhydrophobic (CAwater = 153o) electroactive epoxy (SEE) coatings
was fabricated on the surface of a cold rolled steel (CRS) electrode (Figure 1.18c and d)
using a nanocasting technique with a CP template and an electroactive-epoxy polymer
solution as the ink.78
The SEE coating material not only shows superior water repellent
properties but also had electroactive properties. It should also be noted that the CRS
coated with SEE was found to exhibit remarkably enhanced corrosion protection on the
basis of a series of electrochemical corrosion measurements performed under saline
conditions.78
1.4.2. Template-free Method
Another interesting feature of electro-active materials is that the surface
morphology of the electro-grafted material can be influenced by a variety of parameters
including scan rate, concentrations of monomers, and solvents.79
For example, it was
discovered that PANI nanotubes could be synthesized by a conventional in-situ doping
polymerization in the presence of b-naphthalene sulfonic acid (b-NSA) as the dopant
without using a template, i.e. direct approach, or a template-free method.54a,80
The
template-free method is simple and inexpensive since it requires no template and no post-
treatment. Various micro/nanostructures of conducting polymers, such as nanotubes,
nanofibers, hollow spheres, and even nanotube junctions, have been successfully
synthesized by the template-free method.81
These results provided strong evidence to
support the template-free method as a universal approach to the fabrication of conducting
polymer micro/nanostructures.81d,81h
33
Figure 1.19. (a) SEM image of the rambutan-like hollow PANI spheres (inset a
photograph of a rambutan). (b) Shape of a water droplet on a surface of the rambutan-like
PANI hollow spheres. Reprinted with permission from ref 82a. Copyright 2007 Wiley.
As mentioned earlier, superhydrophobic surfaces are usually obtained by
combining dual scale roughness with a relatively hydrophobic material. Another way to
design superhydrophobic surfaces is to use micelles that serve as a soft-template and the
molecular interactions as the driving forces. For example, Zhu et al. reported the
fabrication of conductive and superhydrophobic rambutan-like hollow spheres (Figure
1.19) of PANI coated surfaces prepared by a self-assembly method in the presence of
perfluorooctane sulfonic acid (PFOSA).82a
Here PFOSA served as a dopant, soft
template, and induced superhydrophobicity at the same time.82a
Based on the above ideas,
conductive and superhydrophobic 3D microstructures assembled from 1D nanofibers of
PANI, such as hollow rambutan-like spheres (Figure 1.19), hollow dandelion-like and
hollow cubebox-like 3D microstructures, have been synthesized.82
34
Figure 1.20. Structures of electroactive monomers: (a) pyrole, (b) ethylenedioxypyrole,
(c) propylenedioxypyrole, (d) thiophene, (e) ethylenedioxythiophene derivatives.
Similarly, Darmanin and Guittard have done extensive work on the subject of
template-free electro-grafting using low energy materials in order to create either
hydrophobic or oleophobic surfaces.83
In their works, Darmanin and Guittard examined
the use of fluorinated pyrrole, ethylenedioxypyrole, propylenedioxypyrole, thiophene,
and ethylenedioxythiophene derivatives (Figure 1.20a-e respectively) in order to create
superhydrophobic surfaces. The explanation for their success was the dual scale
roughness (Figure 1.21a and b) that was achieved by a simple one step electro-grafting
procedure.83
Even more recently, superhydrophobic surfaces using a terthiophene derivative
containing a tertiary bromide moiety able to perform SI-ATRP has been reported. From
this work they found that in order to create superhydrophobic surfaces using this material
that a mixed solution of commercially available terthiophene (5 mM) and the
35
terthiophene with the ATRP moiety (5 mM). From these surface SI-ATRP of NIPAM
revealed that the once superhydrophobic surface became superhydrophilic (CAwater = 0o).
Applications of superhydrophilic surfaces include, anti-fogging, bio-fouling prevention
and release, biomaterials, and enhanced boiling heat transfer.84
Figure 1.21. SEM images of electro-grafted polymers from (a) side (b) and top view.
Reprinted with permission from ref 83h. Copyright 2012 American Chemical Society.
1.5. Chapter Outlines and Objectives
The objectives of this dissertation are as follows: (1) to prepare colloidally
templated polymer brush surfaces using the ‘grafting from” approach (SIP) and the
complementary “grafting to” methods with click chemistry, (2) utilize the electro-grafting
polymerization method to fabricate superhydrophobic surfaces with optimized
parameters, (3) investigate the wetting behavior vis-à-vis morphologies of these
polymerized new monomers, (5) test the specific applications of the superhydrophobic
36
coating towards anti-corrosion and biocidal properties, (6) and use polymer brushes
containing electro-active terthiophene pendants to demonstrate the feasibility of electro-
nanopatterning on electrode surfaces using CS-AFM.
Chapter 2 demonstrates the fabrication of patterned binary polymer brushes via
colloidal particle templating combined with electrodeposited ATRP, RAFT, and ROMP
initiators. From the hexagonally close-packed template and subsequent patterned arrays,
SIP demonstrated novel non-lithographically and laterally patterned binary polymer
brush composition.
Chapter 3 showed a new approach of creating topologically and well-defined
patterned polymeric surfaces via the “grafting to” approach. This was accomplished by
either using colloidally templated “clickable” arrays, whereby the chemistry was
performed directly onto the pattern or by subsequent backfilling with azido terminated
SAM’s. Similarly, direct grafting of electroactive temperature responsive oligo(ethylene
glycol) methacrylic polymers to colloidally templated surfaces allowed for tunable ion
gate formation.
Chapter 4 reports on a novel one-step approach to fabricate superhydrophobic and
superoleophilic electrodeposited coatings. By performing additional SI-ATRP from the
coating, a further change in wettability of the substrates to a variety of liquids was
observed.
Chapter 5 reports on the fabrication of polymerizable superhydrophobic coating
by using a facile one-step procedure, i.e. electrodeposition. These coatings exhibited
37
tunable bacterial adhesion, self-cleaning capabilities, and corrosion resistance. Similarly,
due to the incorporation of an ATRP moiety within the superhydrophobic coating,
surface initiated ATRP of 3,3,4,4,5,5,6,6,7,7,8,8,9,9,10,10,10-heptadecafluorodecyl
methacrylate (HDFM) was performed on a steel slide. Subsequent static water,
diiodomethane, and hexadecane contact angles revealed that the steel coated surface was
superamphiphobic.
Chapter 6 demonstrates electro-nanopatterning of terthiophene pendent containing
polymer brushes that were grown using SI-RAFT polymerization. The nanopatterning
was achieved using CS-AFM in which different applied voltages and writing speeds were
optimized together with the formation of complex nanopatterns.
Finally, Chapter 7 provides important summaries of the projects mentioned in
chapters 2 thru 6 and a global conclusion of the dissertation including future research
work.
1.7. References
1. (a) Shirakawa, H.; Louis, E. J.; MacDiarmid, A. G.; Chiang, C. K.; Heeger, A. J. J.
Chem. Soc., Chem. Commun. 1977, 578. (b) Chiang, C. K.; Park, Y. W.; Heeger, A.
J.; Shirakawa, H.; Louis, E. J.; MacDiarmid, A. G. Phys. Rev. Lett. 1977, 39, 1098.
2. Heinze, J.; Uribe, B. A.-F.; Ludwigs, S. Chem. Rev. 2010, 110, 4724.
3. (a) Delamar, M.; Lacaze, P. C.; Dumousseau, J. S.; Dubois, J. E. Electrochim. Acta
1982, 27, 61. (b) Wnek, G. E.; Chien, J. C. W.; Karasz, F. E.; Lillya, C. P. Polymer
1979, 20, 1441. (c) Diaz, A. F.; Kanazawa, K. K.; Gardini, G. P. J. Chem. Soc.,
38
Chem. Commun. 1979, 635. (d) Diaz, A. F.; Logan, J. A. J. Electroanal. Chem.
1980, 111, 111.
4. (a) Heywang, G.; Jonas, F. Adv. Mater. 1992, 4, 116. (b) Dietrich, M.; Heinze, J.;
Heywang, G.; Jonas, F. J. Electroanal. Chem. 1994, 369, 87.
5. (a) Diaz, A. F.; Kanazawa, K. K.; Gardini, G. P. J. Chem. Soc., Chem. Commun.
1979, 635. (b) Diaz, A. F. Chem. Scr. 1981, 17, 142. (c) Tourillon, G.; Garnier, F. J.
Electroanal. Chem. 1982, 135, 173. (d) Diaz, A. F.; Logan, J. A. J. Electroanal.
Chem. 1980, 111, 111. (e) Noufi, R.; Nozi, A. J.; White, J.; Warren, L. F. J.
Electrochem. Soc. 1981, 129, 2261.
6. (a) Diaz, A. F.; Castillo, J. I.; Logan, J. A.; Lee, W. Y. J. Electroanal. Chem. 1981,
129, 115. (b) Genies, E. M.; Bidan, G.; Diaz, A. F. J. Electroanal. Chem. 1983,
149, 101.
7. (a) Skotheim, T. A., Reynolds, J. R., Eds. Handbook of Conducting Polymers, 3rd
ed.; CRC Press: Boca Raton, FL, 2007. (b) Inzelt, G. Conducting Polymers;
Springer: Heidelberg, 2008. (c) Narula, P. M.; Noftle, R. E. J. Electroanal. Chem.
1999, 464, 123. (d) Sadki, S.; Schottland, P.; Brodie, N.; Sabouraud, G. Chem. Soc.
Rev. 2000, 29, 283.
8. Andrieux, C. P.; Audebert, P.; Hapiot, P.; Savéant, J.-M. J. Phys. Chem. 1991, 95,
10158
9. (a) Heinze, J.; John, H.; Dietrich, M.; Tschuncky, P. Synth. Met. 2001, 119, 49. (b)
Heinze, J. In Encyclopedia of Electrochemistry; Bard, A. J., Stratmann, M., Eds.;
Wiley-VCH: Weinheim, Germany, 2004; Vol. 8, Chapter 16, p 607. (c) Smie, A.;
39
Synowczyk, A.; Heinze, J.; Alle, R.; Tschuncky, P.; Götz, G.; Bäuerle, P. J.
Electroanal. Chem. 1998, 452, 87.
10. Lukkari, J.; Alanko, M.; Pitkänen, V.; Kleemola, K.; Kankare, J. J. Phys. Chem.
1994, 98, 8525.
11. Gorelikov, I.; Kumacheva, E. Chem. Mater. 2004, 16, 4122.
12. Mrozek, M. F.; Xie, Y.; Weaver, M. J. Anal. Chem. 2001, 73, 5953.
13. (a) Bund, A.; Baba, A.; Berg, S.; Johannsmann, D.; Lübben, J.; Wang, Z.; Knoll,
W. J. Phys. Chem. B 2003, 107, 6743. (b) Efimov, I.; Winkels, S.; Schultze, J. W. J.
Electroanal. Chem. 2001, 499, 169. (c) Kvarnström, C.; Bilger, R.; Ivaska, A.;
Heinze, J. Electrochim. Acta 1998, 43, 355. (d) Skompska, M. Electrochim. Acta
2000, 45, 3841.
14. (a) Milner, S. T. Science 1991, 251, 905. (b) Halperin, A.; Tirrell, M.; Lodge, T. P.
Adv. Polym. Sci. 1992, 100, 31. (c) Brittain, W. J.; Minko, S. J. Polym. Sci., Part A:
Polym. Chem. 2007, 45, 3505. Zhao, B.; Brittain, W. J. Prog. Polym. Sci. 2000, 25,
677.
15. (a) Tsukruk, V. V. Prog. Polym. Sci. 1997, 22, 247. (b) Brandani, P.; Stroeve, P.
Macromolecules 2004, 37, 6640. (c) Kenausis, G. L.; Vörös, J.; Elbert, D. L.;
Huang, N. P.; Hofer, R.; Ruiz-Taylor, L.; Textor, M.; Hubbell, J. A.; Spencer, N. D.
J. Phys. Chem. B 2000, 104, 3298. (d) Huang, N.-P.; Michel, R.; Voros, J.; Textor,
M.; Hofer, R.; Rossi, A.; Elbert, D. L.; Hubbell, J. A.; Spencer, N. D. Langmuir
2001, 17, 489. (e) Elbert, D. L.; Hubbell, J. A. Chem. Biol. 1998, 5, 177. (f) Lee, S.;
Vörös, J. Langmuir 2005, 21, 11957. (g) Brandani, P.; Stroeve, P. Macromolecules
40
2003, 36, 9492. (h) Brandani, P.; Stroeve, P. Macromolecules 2003, 36, 9502. (i)
Papra, A.; Gadegaard, N.; Larsen, N. B. Langmuir 2001, 17, 1457. (j) Tran, Y.;
Auroy, P. J. Am. Chem. Soc. 2001, 123, 3644. (k) Sofia, S. J.; Premnath, V.;
Merrill, E. W. Macromolecules 1998, 31, 5059. (l) Luzinov, I.; Julthongpiput, D.;
Malz, H.; Pionteck, J.; Tsukruk, V. V. Macromolecules 2000, 33, 1043. (m) Minko,
S.; Patil, S.; Datsyuk, V.; Simon, F.; Eichhorn, K.-J.; Motornov, M.; Usov, D.;
Tokarev, I.; Stamm, M. Langmuir 2002, 18, 289. (n) Zhu, B.; Eurell, T.; Gunawan,
R.; Leckband, D. J. Biomed. Mater. Res. 2001, 56, 406. (o) Ostuni, E.; Yan, L.;
Whitesides, G. M. Colloids Surf., B 1999, 15, 3. (p) Roberts, C.; Chen, C. S.;
Mrksich, M.; Martichonok, V.; Ingber, D. E.; Whitesides, G. M. J. Am. Chem. Soc.
1998, 120, 6548.
16. Balazs, A. C.; Singh, C.; Zhulina, E.; Chern, S.-S.; Lyatskaya, Y.; Pickett, G. Prog.
Surf. Sci. 1997, 55, 181.
17. (a) Advincula, R. C. J. Dispersion Sci. Technol. 2003, 24, 343. (b) Jennings, G. K.;
Brantley, E. L. Adv. Mater. 2004, 16, 1983. (c) Radhakrishnan, B.; Ranjan, R.;
Brittain, W. J. Soft Matter 2006, 2, 386.
18. (a) Matyjaszewski, K. Prog. Polym. Sci. 2005, 30, 858. (b) Braunecker, W. A.;
Matyjaszewski, K. Prog. Polym. Sci. 2007, 32, 93. (c) Edmondson, S.; Osborne, V.
L.; Huck, W. T. S. Chem. Soc. Rev. 2004, 33, 14. (d) Tsujii, Y.; Ohno, K.;
Yamamoto, S.; Goto, A.; Fukuda, T. Adv. Polym. Sci. 2006, 197, 1. (e) Pyun, J.;
Kowalewski, T.; Matyjaszewski, K. Macromol. Rapid Commun. 2003, 24, 1043. (f)
Pyun, J.; Matyjaszewski, K. Chem. Mater. 2001, 13, 3436.
41
19. (a) Perrier, S.; Takolpuckdee, P. J. Polym. Sci., Part A: Polym. Chem. 2005, 43,
5347. (b) Chiefari, J.; Chong, Y. K.; Ercole, F.; Krstina, J.; Jeffery, J.; Le, T. P. T.;
Mayadunne, R. T. A.; Meijs, G. F.; Moad, C. L.; Moad, G.; Rizzardo, E.; Thang, S.
H. Macromolecules 1998, 31, 5559. (c) Moad, G.; Rizzardo, E.; Thang, S. H. Aust.
J. Chem. 2005, 58, 379.
20. Baum, M.; Brittain, W. J. Macromolecules 2002, 35, 610.
21. (a) Yu, W. H.; Kang, E. T.; Neoh, K. G. Ind. Eng. Chem. Res. 2004, 43, 5194. (b)
Zhai, G. Q.; Yu, W. H.; Kang, E. T.; Neoh, K. G.; Huang, C. C.; Liaw, D. J. Ind.
Eng. Chem. Res. 2004, 43, 1673. (c) Chen, Y. W.; Sun, W.; Deng, Q. L.; Chen, L.
J. Polym. Sci., Part A: Polym. Chem. 2006, 44, 3071. (d) Yoshikawa, C.; Goto, A.;
Tsujii, Y.; Fukuda, T.; Yamamoto, K.; Kishida, A. Macromolecules 2005, 38, 4604.
22. Grande, C. D.; Tria, M. C.; Jiang, G.; Ponnapati, R.; Advincula, R. Macromolecules
2011, 44, 966.
23. Tria, M. C. R.; Grande, C. D. T.; Ponnapati, R. R. Advincula, R. C.
Biomacromolecules 2010, 11, 3422.
24. Tria, M. C.; Liao, K.-S.; Alley, N.; Curran, S.; Advincula, R. J. Mater. Chem. 2011,
21, 10261.
25. Patton, D. L.; Taranekar, P.; Fulghum, T.; Advincula, R. Macromolecules 2008, 41,
6703.
26. (a) Wang, J.-S.; Matyjaszewski, K. J. Am. Chem. Soc. 1995, 117, 5614. (b) Kato,
M.; Kamigaito, M.; Sawamoto, M.; Higashimura, T. Macromolecules 1995, 28,
1721. (c) Percec, V.; Barboiu, B. Macromolecules 1995, 28, 7970. (d) Patten, T. E.;
42
Matyjaszewski, K. Adv. Mater. 1998, 10, 901. (e) Patten, T. E.; Matyjaszewski, K.
Acc. Chem. Res. 1999, 32, 895. (f) Matyjaszewski, K.; Xia, J. H. Chem. Rev. 2001,
101, 2921. (g) Kamigaito, M.; Ando, T.; Sawamoto, M. Chem. Rev. 2001, 101,
3689. (h) Tsarevsky, N. V.; Matyjaszewski, K. Chem. Rev. 2007, 107, 2270.
27. Huang, X. Y.; Wirth, M. J. Anal. Chem. 1997, 69, 4577.
28. Sedjo, R. A.; Mirous, B. K.; Brittain, W. J. Macromolecules 2000, 33, 1492.
29. (a) Wang, Y.-P.; Pei, X.-W.; He, X.-Y.; Lei, Z.-Q. Eur. Polym. J. 2005, 41, 737. (b)
Wang, Y.-P.; Pei, X.-W.; Yuan, K. Mater. Lett. 2005, 59, 520.
30. Matrab,T.; Chehimi, M. M.; Perruchot,C.; Adenier, A.; Guillez, A.; Save, M.;
Charleux, B.; Deliry, E. C.; Pinson, J. Langmuir 2005, 21, 4686.
31. Foster, E. L.; Tria, M. C. R.: Pernites, R. B.; Addison, S. J.; Advincula, R. C. Soft
Matter 2012, 8, 353.
32. Hérisson, J. L.; Chauvin, Y. Makromol. Chem. 1971, 141, 161.
33. (a) Schrock, R. R.; Murdzek, J. S.; Bazan, G. C.; Robbins, J.; DiMare, M.;
O’Regan, M. J. Am. Chem. Soc. 1990, 112, 3875. (b) Schrock, R. R. Tetrahedron
1999, 55, 8141.
34. Vougioukalakis, G. C.; Grubbs, R. H. Chem. Rev. 2010, 110, 1746.
35. (a) Trnka, T. M.; Grubbs, R. H. Acc. Chem. Res. 2001, 34, 18. (b) Totland, K. M.;
Boyd, T. J.; Lavoie, G. G.; Davis, W. M.; Schrock, R. R. Macromolecules 1996, 29,
6114. (c) Buchmeiser, M. R. Chem. Rev. 2000, 100, 1565. (d) Frenzel, U.; Nuyken,
O. J. Polym. Sci. A –Polym. Chem. 2002, 40, 2895. (e) Choi, T. L.; Grubbs, R. H.
Angew. Chem. Int. Ed. 2003, 42, 1743. (f) Bielawski, C. W.; Grubbs, R. H. Progr.
43
Polymer. Sci. 2007, 32. 1. (g) Breslow, D. S. Progr. Polym. Sci. 1993, 18, 1141. (h)
Gibson, V. C. Adv. Maiste, A. L. Progr. Polym. Sci. 1997, 22, 601. (i) Feast, W. J.;
Khosravi, E. J. Fluor. Chem. 1999, 100, 117. (j) Marciniec, B.; Pietraszuk, C. Curr.
Org. Chem. 2003, 7, 691.
36. (a) Edmondson, S.; Osborne, V. L.; Huck, W. T. S. Chem. Soc. Rev. 2004, 33, 14.
(b) Senaratne, W.; Andruzzi, L.; Ober, C. K.; Biomacromolecules 2005, 6, 2427. (c)
Advincula, R. C. J. Disper. Sci. Technol. 2003, 113, 343. (d) Ruckenstein, E.; Li, Z.
F. Adv. Colloid. Interfac. 2005, 113, 43. (e) Radhakrishnan, B.; Ranjan, R.; Brittain,
W. J. Soft Matter 2006, 2, 386. (f) Jennings, G. K.; Brantley, E. L.; Adv. Mater.
2004, 16, 1983. (g) Minko, S.; Polym. Rev. 2006, 46, 397. (h) Hansen, N. M. L.;
Jankova, K.; Hvilsted, S. Eur. Polym. J. 2007, 43, 255. (i) Tsubokawa, N. Polym. J.
2005, 37, 637. (j) Aoshima, S. Wax. Cryst. Contr. 2008, 210, 169. (k) Edmondson,
S.; Armes, S. P. Polym. Int. 2009. 58, 307.
37. Jiang, G.; Ponnapati, R.; Pernites, R.; Felipe, M. J.; Advincula, R. Macromolecules
2010, 43, 10262.
38. Kolb, H. C.; Finn, M. G.; Sharpless, K. B.; Angew. Chem. Int. Ed. 2001, 40, 2004.
39. (a) Huisgen, R. Angew. Chem. 1963, 75, 604. (b) Huisgen, R. Angew. Chem. 1963,
75, 742.
40. Törne, C. W.; Christensen, C.; Meldal, M. J. Org. Chem. 2002, 67, 3057.
41. V. V. Rostovtsev, L. G. Green, V. V. Fokin, K. B. Sharpless, Angew. Chem, Int.
Ed. 2002, 41, 2596.
44
42. (a) Kolb, H. C.; Sharpless, K. B. Drug Discov. Today 2003, 8, 1128. (b) Binder, W.
H.; Sachsenhofer, R. Macromol. Rapid Commun. 2007, 28, 15. (c) Bock, V. D.;
Hiemstra, H.; Van Maarseveen, J. H. Eur. J. Org. Chem. 2006, 51. (d) Lutz, J.-F.;
Zarafshani, Z. Adv. Drug Deliv. Rev. 2008, 60, 958. (d) Hawker, C. J.; Wooley, K.
L. Science 2005, 309, 1200. (e) Binder, W. H.; Kluger, C. Curr. Org. Chem. 2006,
10, 1791.
43. (a) Tietze, L. F.; Kettschau, G. Top. Curr. Chem. 1997, 189, 1. (b) Walsmann, H.
Synthesis 1994, 535.
44. (a) Kagabu, S.; Kaiser, C.; Keller, R.; Becker, P. G.; Mueller, K. H.; Knothe, L.;
Rihs, G.; Prinzbach, H. Chem. Ber. 1988, 121, 741. (b) Suami, T.; Ogawa, S.;
Uchino, H.; Funaki, Y. J. Org. Chem. 1975, 40, 456. (c) Vogel, E.; Kuebart, F.;
Marco, J. A.; Andree, R. J. Am. Chem. Soc. 1983, 105, 6982.
45. Im, S. G.; Bong, K. W.; Kim, B.-S.; Baxamusa, S. H.; Hammond, P. T.; Doyle, P.
S.; Gleason, K. K. J. Am. Chem. Soc. 2008, 130, 14424.
46. (a) Adolfsson, H.; Converso, A.; Sharpless, K. B. Tetrahedron Lett. 1992, 40, 3991.
(b) Katsuki, T.; Martin, V. S. Org. React. 1996, 48, 1. (c) Katsuki, T. J. Mol. Catal.
A 1996, 113, 87. (d) Kolb, H. C.; Van Nieuwenhze, M.; Sharpless, K. B. Chem.
Rev. 1994, 94, 2483. (e) Jeong, U.; Tao, B.; Sagasser, I.; Henniges, H.; Sharpless,
K. B. J. Am. Chem. Soc. 1998, 120, 6844. (f) Evans, D. A.; Faul, M. M.; Bilodeau,
M. T. J. Org. Chem. 1991, 56, 6744.
47. (a) Lutz, J.-F. Angew. Chem, Int. Ed. 2007, 46, 1018. (b) Devaraj, N. K.; Collman,
J. P.; QSAR Comb. Sci. 2007, 26, 1253. (c) Ciampi, S.; Böcking, T.; Kilian, K. A.;
45
Janes, M.; Harper, J. B.; Gooding, J. J. Langmuir 2007, 23, 9320. (d) Collman, J. P.;
Devaraj, N. K.; Chidsey, C. E. D. Langmuir 2004, 20, 1051. (e) Marrani, A. G.;
Dalchiele, E. A.; Zanoni, R.; Decker, F.; Cattaruzza, F.; Bonifazi, D.; Prato, M.
Electrochim. Acta 2008, 53, 3903. (f) Nebhani, L.; Sinnwell, S.; Inglis, A. J.;
Stenzel, M. H.; Barner-Kowollik, C. Macromol. Rapid Commun. 2008, 29, 1431.
48. Kiskan, B.; Gacal, B.; Asan, M.; Gunaydin, E. D.; Yilmaz, I.; Yagci, Y. Polym.
Bull. 2011, 67, 609.
49. Kunz, T. K.; Wolf, M. O. Polym. Chem. 2011, 2, 640.
50. Shon, Y.-S.; Kelly, K. F.; Halas, N. J.; Lee, T. R. Langmuir 1999, 15, 5329.
51. (a) Collman, J. P.; Devaraj, N. K.; Chidsey, C. E. D. Langmuir, 2004, 20, 1051. (b)
Collman, J. P.; Devaraj, N. K.; Eberspacher, T. P. A.; Chidsey, C. E. D. Langmuir,
2006, 22, 2457. (c) Collman, J. P.; Hosseini, A.; Eberspacher, T. P. A.; Chidsey, C.
E. D. Langmuir, 2009, 25, 6517. (d) Hosseini, A.; Collman, J. P.; Devadoss, A.;
Williams, G. Y.; Barile, C. J.; Eberspacher, T. A. Langmuir, 26, 17674.
52. Ofir, Y.; Moran, I. W.; Subramani, C.; Carter, K. R.; Rotello, V. M. Adv. Mater.
2010, 22, 3608.
53. (a) Del Campo, A.; Arzt. E. Chem. Rev. 2008, 108, 911. (b) Jones, D. M.; Smith, J.
R.; Huck, W. T. S.; Alexander, C. Adv. Mater. 2002, 14, 1130. (c) Paul, K. E.;
Prentiss, M.; Whitesides, G. M. Adv. Funct. Mater. 2003, 13, 259. (d) Ahn, S. J.;
Kaholek, M.; Lee, W. K.; LaMattina, B.; LaBean, T. H.; Zauscher, S. Adv. Mater.
2004, 16, 2141. (e) Kaholek, M.; Lee, W. K.; LaMattina, B.; Caster, K. C.;
Zauscher, S. Nano Lett. 2004, 4, 373. (f) Werne, T. A. V.; Germack, D. S.;
46
Hagberg, E. C.; Sheares, V. V.; Hawker, C. J.; Carter, K. R. J. Am. Chem. Soc.
2003, 125, 3831.
54. (a) Martin, C. R. Science 1994, 266, 1966. (b) Martin, C. R. Acc. Chem. Res. 1995,
28, 61.
55. Braun, P. V.; Wiltzius, P. Curr. Opin. Colloid Interface Sci. 2002, 7, 116.
56. Tian, S.; Wang, J.; Jonas, U.; Knoll, W. Chem. Mater. 2005, 17, 5726.
57. Sumida, T.; Wada, Y.; Kitamura, T.; Yanagida, S. Chem. Commun. 2000, 1613.
58. Cassagneau, T.; Caruso, F. Adv. Mater. 2002, 14, 1837.
59. Pernites, R. B.; Venkata, S. K.; Tiu, B. D. B.; Yago, A. C. C.; Advincula, R. C.
Small 2012, 8, 1669.
60. Pernites, R. B.; Felipe, M. J. L.; Foster, E. L.; Advincula, R. C. ACS Appl. Mater.
Interfaces 2011, 3, 817.
61. Felipe, M. J. L.; Ponnapati, R. R.; Pernites, R. B.; Dutta, P.; Advincula, R. C. ACS
Appl. Mater. Interfaces 2010, 2, 3401.
62. Pernites, R. B.; Foster, E. L.; Felipe, M. J. L.; Robinson, M.; Advincula, R. C. Adv.
Mater. 2011, 23, 1287.
63. Foster, E. L. Bunha, A.; Advincula, R. Polymer 2012, 53, 3124.
64. (a) Wuu, Y.-M.; Fan, F.-R.-F.; Bard, A. J. J. Electrochem. Soc. 1989, 136, 885. (b)
Kranz, C.; Ludwig, M.; Gaub, H. E.; Schuhmann, W. Adv. Mater. 1995, 7, 38.
65. Zhou, J.; Wipf, D. O. J. Electrochem. Soc. 1997, 144, 1202.
66. Li, Y.; Maynor, B. W.; Liu, J. J. Am. Chem. Soc. 2001, 123, 2105.
47
67. Maynor, B. W.; Filocamo, S. F.; Grinstaff, M. W.; Liu, J. J. Am. Chem. Soc. 2002,
124, 522.
68. (a) Jegadesan, S.; Advincula, R. C.; Valiyaveettil, S. Adv. Mater. 2005, 17, 1282.
(b) Jegadesan, S.; Sindhu, S.; Advincula, R. C.; Valiyaveettil, S. Langmuir 2006,
22, 780. (c) Jiang, G.; Baba, A.; Advincula, R. Langmuir 2007, 23, 817. (d) Huang,
C.; Jiang, G.; Advincula, R. Macromolecules 2008, 41, 4661. (e) Park, J. Y.;
Ponnapati, R.; Taranekar, P.; Advincula, R. C. Langmuir 2010, 26, 6167. (f) Park, J.
Y.; Taranekar, P.; Advincula, R. Soft Matter 2011, 7, 1 49 1 55.
69. (a) Blossey, R.; Nat. Mater. 2003, 2, 301. (b) Chen, W. ; Fadeev, A. Y.; Hsieh, M.
C.; Oner, D.; Youngblood, J.; McCarthy, T. J. Langmuir 1999, 15, 3395. (c) Callies,
M.; Quere, D. Soft Matter 2005, 1, 55. (d) Feng, L.; Li, S. H.; Li, Y. S.; Li, H. J.;
Zhang, L. J.; Zhai, J.; Song, Y. L.; Liu, B. Q.; Jiang, L.; Zhu, D. B. Adv. Mater.
2002, 14, 1857. (e) Sun, T. L.; Feng, L.; Gao, X.; Jiang, L. Acc. Chem. Res. 2005,
38, 644. (f) Feng, X. J.; Jiang, L. Adv. Mater. 2006, 18, 3063. (g) Ma, M. L.; Hill,
R. M. Curr. Opin. Colloid Interface Sci. 2006, 11, 193. (h) Nakajima, A.;
Hashimoto, K.; Watanabe, T. Monatsh. Chem. 2001, 132, 31. (i) Quere, D. Rep.
Prog. Phys. 2005, 68, 2495.
70. (a) Wenzel, R. N. Ind. Eng. Chem. 1936, 28, 8, 988. (b) Cassie, A. B. D.; Baxter, S.
Trans. Faraday Soc. 1944, 40, 546. (c) Onda, T.; Shibuichi, S.; Satoh, N.; Tsujii, K.
Langmuir 1996, 12, 2125.
48
71. Barthlott, W.; Neinhuis, C. Planta 1997, 202, 1. (b) Drelich, J.; Chibowski, E.;
Meng, D. D.; Terpilowski, K. Soft Matter 2011, 7, 9894. (c) Verplanck, N.;
Coffineir, Y.; Thomy, V.; Boukherroub, R. Nanoscale Res. Lett. 2007, 2, 577.
72. Quere, D.; Lafuma, A.; J. Bico. Nanotechnology 2003, 14, 1109.
73. (a) Shirtcliffe, N. J.; McHale, G.; Newton, M. I.; Perry, C. C. Langmuir 2005, 21,
937. (b) Shirtcliffe, N. J.; Aqil, S.; Evans, C.; McHale, G.; Newton, M. I.; Perry, C.
C.; Roach, P. J. Micromech. Microeng. 2004, 14, 1384. (c) Kusumaatmaja, H.;
Yeomans, J. Langmuir 2007, 23, 6019. (d) Li, W.; Amirfazli, A. Adv. Colloid
Interface Sci. 2007, 132, 51. (e) Marmur, A. Langmuir 2004, 20, 3517. (f) Extrand,
C. Langmuir 2002, 18, 7991. (g) He, B.; Lee, J.; Patankar, N. Colloids Surf. A.
2004, 248, 101. (h) Gao, L.; McCarthy, T. Langmuir 2006, 22, 6234. (i)
Bormashenko, E.; Pogreb, R.; Whyman, G.; Erlich, M. Langmuir 2007, 23, 6501.
74. (a) Sun. T. L.; Feng, L.; Gao, X. F.; Jiang, L. Acc. Chem. Res. 2005, 38, 644. (b)
Puretsky, N.; Ionov, L. Langmuir 2011, 27, 3006. (c) Xiong, D.; Liu, G.; Hong, L.
Chem. Mater. 2011, 23, 4357. (d) Shiu, J. Y.; Kuo, C. W.; Chen, P.; Mou, C. Y.
Chem. Mater. 2004, 16, 561.
75. Xiong, D.; Liu, G.; Hong, L. Chem. Mater. 2011, 23, 4357.
76. (a) Pernites, R. B.; Ponnapati, R. R.; Advincula, R. C. Adv. Mater. 2011, 23, 3207.
(b) de Leon, A. C. C.; Pernites, R. B.; Advincula, R. C. ACS Appl. Mater. Interfaces
2012, ASAP article.
77. Pernites, R. B.; Santos, C. M.; Maldonado, M.; Ponnapati, R. R.; Rodriques, D. F.;
Advincula, R. C. Chem. Mater. 2012, 24, 870.
49
78. Weng, C. -J.; Chang, C. -H.; Peng, C. -W.; Chen, S. -W.; Yeh, J. -M.; Hsu, C. -L.;
Wei, Y. Chem. Mater. 2011, 23, 2075.
79. Wan, M. Adv. Mater. 2008, 20, 2926.
80. Wan, M. X.; Shen, Y. Q.; Huang, J. Chinese Patent No. 98109916.5, 1998.
81. (a) Huang, J.; Wan, M. X. J. Poly. Sci, Part A: Polym. Chem. 1999, 37, 1277. (b)
Wei, Z. X.; Wan, M. X. J. Appl. Polym. Sci. 2003, 87, 1297. (c) Zhang, Z. M.; Wei,
Z. X.; Wan, M. X. Macromolecules 2002, 35, 5937. (d) Wei, Z. X.; Wan, M. X.
Adv. Mater. 2002, 14, 1314. (e) Wei, Z. X.; Zhang, L. J.; Yu, M.; Yang, Y. S.; Wan,
M. X. Adv. Mater. 2003, 15, 1382. (f) Shen, Y. Q.; Wan, M. X. J. Polym. Sci, Part
A: Polym. Chem. 1997, 35, 3689. (g) Liu, J.; Wan, M. X. J. Mater. Chem. 2001, 11,
404. (h) Zhang, L.; Wan, M. X. Adv. Funct. Mater. 2003, 13, 815. (i) Yang, Y. S.;
Wan, M. X.; J. Mater. Chem. 2001, 11, 2022.
82. (a) Zhu, Y.; Hu, D.; Wan, M. X.; Lei, J.; Wei, Y. Adv. Mater. 2007, 19, 2092. (b)
Zhu, Y.; Li, J. M.; Wan, M. X.; Jiang, L. Macromol. Rapid. Commun. 2008, 29,
239.
83. (a) Darmanin, T.; Guittard, F. J. Am. Chem. Soc. 2009, 131, 7928. (b) Darmanin, T.;
Guittard, F. J. Mater. Chem. 2009, 19, 7130. (c) Darmanin, T.; Guittard, F. J.
Colloid Interface Sci. 2009, 335, 146. (d) Darmanin, T.; Taffin de Givenchy, E.;
Guittard, F. Macromolecules 2010, 43, 9365. (e) Darmanin, T.; Guittard, F.
Langmuir 2009, 25, 5463. (f) Darmanin,T.; Taffin de Givenchy,E.;Amigoni, S.;
Guittard, F. Langmuir 2010, 26, 17596. (g) Darmanin, T.; Nicolas, M.; Guittard, F.
50
Langmuir 2008, 24, 9739. (h) Bellanger, H.; Darmanin, T.; Guittard, F. Langmuir
2012, 28, 186.
84. (a) Yang, X. G.; Zhang, F. Y.; Lubawy, A. L.; Wang, C. Y. Electrochem. Solid-
State Lett. 2004, 7, 408. (b) Maharbiz, M.; Holtz, W. J.; Howe, R. T.; Keasling, J.
D. Biotechnol. Bioeng. 2004, 85, 376. (c) Baier, R. J. Mater. Sci.: Mater.
Med. 2006, 17, 1057. (d) Hasuda, H.; Kwon, O. H.; Kang, I. K.; Ito, Y.
Biomaterials 2005, 26, 2401. (e) Li, C.; Wang, Z.; Wang, P. I.; Peles, Y.; Koratkar,
N.; Peterson, G. P. Small 2008, 4, 1084. (f) Chen, R.; Lu, M. –C.; Srinivasan, V.;
Wang, Z.; Cho, H. H.; Majumdar, A. Nano Lett. 2009, 9, 548.
51
Chapter 2: Patterned Polymer Brushes via Electrodeposited ATRP,
ROMP, and RAFT Initiators on Colloidal Template Arrays
2.1. Introduction
Surface patterning is of high interest in device technologies and applications
including sensors, biochips, displays, and microfluidic systems.1 Also of high interest are
polymer films, known as “polymer brush” systems. Polymer brushes have drawn
significant attention because of the wide range of mechanisms suitable for surface
initiated polymerization (SIP) and the physical/mechanical properties of the grafted films.
Several polymerization techniques for producing polymer brush surfaces have
gained popularity. For example, atom transfer radical polymerization (ATRP) is very
much suited for polymer brush synthesis due to excellent control over brush thickness
and polydispersity. Moreover, it allows the preparation of block copolymer brushes
through re-initiation of dormant chain ends.2 The use of ATRP has been exploited
frequently to prepare bottle brush architectures but has more recently been employed for
surface functionalization.3 Complementary to ATRP, reversible-addition fragmentation
chain transfer (RAFT) polymerization is based on a chain transfer agent.4 A distinct
advantage of RAFT polymerization is its relative simplicity and versatility. RAFT
polymerization has also been successfully used to prepare polymer brushes via SIP.
Another polymerization technique that can be used to create polymer brushes is via
52
surface-initiated ring-opening metathesis polymerization (SI-ROMP), which utilizes late
transition metal catalysts.5
As a living/controlled polymerization technique, SI-ROMP
offers the capability of preparing uniform polymer brushes and block copolymers by
metathesis methods.
Figure 2.1. Structures of (a) 3,5-bis(4-(9H-carbazol-9-yl)butoxy)benzyl 2-bromo-2-
methylpropanoate (Cbz-Initiator), (b) 3,5-bis (4-(9H-carbazol-9-yl) butoxy) benzyl 4-
cyano-4 (phenylcarbonothioylthio) pentanoate (Cbz-CTA), and (c) Bicyclo[2.2.1]hept-5-
en-2-ylmethyl 3,5-Bis- (4-(9H-carbazol-9-yl) butoxy) benzoate (Cbz-Nb).
Most polymer brush patterning protocols can be complicated or time consuming:
lithographic techniques such as soft-lithography, electron-beam (e-beam) lithography,
scanning probe lithography, and imprint lithography.6-10
Moreover, multi-compositioned
and patterned brushes are not very common. A technique that has been under utilized for
two-dimensional (2D) surface patterning is the use of ordered colloidal crystal templates.
Object formation or porogenic templating has been done on ordered colloidal crystals that
serve as sacrificial templates (colloidal templating) for structuring inverse three-
dimensional (3D) colloidal arrays. Other 3D sacrificial templates can come from a variety
53
of materials including anodized alumina, block copolymers, and inorganic or organic
colloidal spheres.11-13
Among them, the polymer colloidal spheres, i.e. polystyrene (PS)
microspheres, are of interest, because they are easy to handle and are commercially
available. Following the formation of the ordered colloidal crystals, a variety of materials
have been used to fill-in the interstitial void spaces in-between the arrays. For example,
metals, inorganic oxides, diamond and glassy carbon, or conducting polymers have all
been templated.14-16
The use of conducting polymers is of high interest because of their
tuneable electro-optical and chemical properties.
This chapter reports the first approach of utilizing both colloidal templating and
the electrodeposition of electroactive initiators, 3,5-bis(4-(9H-carbazol-9-
yl)butoxy)benzyl 2-bromo-2-methylpropanoate (Cbz-Initiator), 3,5-bis (4-(9H-carbazol-
9-yl) butoxy) benzyl 4-cyano-4 (phenylcarbonothioylthio) pentanoate (Cbz-CTA), and
Bicyclo[2.2.1]hept-5-en-2-ylmethyl 3,5-Bis-(4-(9H-carbazol-9-yl) butoxy) benzoate
(Cbz-Nb) Figure 2.1a-c respectively, were upon electrodeposition, the films become a
conjugated polymer network (CPN) based on the bifunctional carbazole, f = 4 (Figure
2.2a).17
The built-in ATRP, RAFT, or ROMP moiety allowed the formation of patterned
polymer brush systems via SIP of methyl methacrylate (MMA), styrene (PS), or
norbornene (Nb) monomers from the inverse colloidal Cbz-Intiator, -CTA, -Nb arrays
respectively.
54
2.2. Results and Discussion
2.2.1. Formation of Inverse Colloidal Cbz-Intiator Arrays
The procedure for the stepwise formation of patterned polymer brush surfaces is
illustrated in Figure 2.2b. First, a monolayer of polystyrene (PS) sub-microspheres
particles (500 nm) were deposited on a conducting indium tin oxide (ITO) substrate using
Figure 2.2. (a) General structure of the electro-active functional initiators before and
after electrodeposition forming the polycarbazole network. (b) Fabrication of a highly
ordered monolayer of colloidal crystals (500 nm diameter PS microspheres), inverse
colloidal arrays, and patterned polymer brushes via SIP.
55
the so-called Langmuir-Blodgett (LB)-like technique,18
which requires a vertical lifting
motor. The LB-like technique allows the monolayer deposition of particles in
hexagonally closed-packing arrangement onto the planar substrate, which will later serve
as a template for electrodeposition. It has been found that the vertical drawing speed of
the LB-like technique and the concentration of the particles and surfactant (sodium n-
dodecyl sulfate or SDS) in solution are vital for the successful formation of a highly
ordered assembly of the microsphere particles on the surface.18
It should be noted that in
order to maintain the hexagonal arrangement of the PS during the electrodeposition step,
it is necessary that a compatible solvent like acetonitrile (ACN) is used. Other solvents
such as water or tetrahydrofuran (THF) tend to wash the particles and destroy the
ordering of the initial PS patterned surface.
The first molecule to be electrodeposited was the Cbz-Initiator. Electrodeposition
was achieved via chronoamperometry using an applied constant potential of 1.3 V for 3
min. This step was followed by a monomer-free scan to further confirm the presence of
the electrodepositied film (Figure 2.3a). Moreover, the UV-vis spectrum (Figure 3b) of
the electrodeposited film after removal of the PS, reveals the signature peaks of a typical
cross-linked polycarbazole network film on ITO with peaks centered at 430 and >800
nm, which is consistent with our group’s previous studies on CPN formation.17
These
peaks are assigned to the to ∗ transition of the polycarbazole and the polaronic band
formation of the conjugated polycarbazole and their redox ion couple with the
hexafluorophosphate ions respectivly.17,19
56
Figure 2.3. (a) Representative I-T curve of the electrodeposition via chronoamperometry
at a constant potential of 1.3 V for 3 min and the subsequent monomer free scan (inset).
(b) UV-vis spectrum of inverse colloidal Cbz-Initiator arrays after electrodeposition.
The advantage of using electrodeposition is that the macroinitiator is only
deposited at the interstitial void spaces between the hexagonally packed PS particles
(Figure 2.4a). The PS particles were then removed by washing with THF (2X, 30 min).
The removal of the sacrificial PS particles created the 2D inverse colloidal Cbz-Initiator
arrays. Atomic force microscopy (AFM) topography measurements of the inverse
colloidal Cbz-Initiator arrays depict a high periodicity of the PS imprinted film (Figure
57
2.4b). The size of the cavity matches the size of the PS particle template as determined by
the AFM line profile (Figure 2.4d and e). The AFM line profile also showed that the
average height of the cavity before polymerization was 10.5 ± 0.7 nm (Figure 2.4e and
f).
2.2.2. Surface-initiated Polymerization of MMA via ATRP
To create a highly ordered patterned polymer brush films, surface initiated (SI-
ATRP) was done on the inverse colloidal Cbz-Initiator arrays (Figure 2.4c). From the
AFM topography image the morphology has changed from the hexagonal array (Figure
2.4b), to a relatively spherical void with a more granular appearance on the periphery of
the patterned area (Figure 2.4c). The AFM line profiles (Figure 2.4f) before and after
brush growth also show an increase in the in the patterned film thickness from 10.5 ± 0.7
nm to 25.3 ± 1.6 nm.
High resolution XPS scans also confirmed the successful polymerization of
MMA. As seen in Figure 2.5a, the deconvolution of the C 1s peak after polymerization
of MMA (inset) reveals a considerable increase in the O–C=O peak situated at ~289 eV
as compared to the inverse colloidal Cbz-Initiator array film.20
Also of interest is the
drastic increase in the intensity of the O 1s peak after polymerization of MMA (Figure
2.5b). This increase is attributed to the higher concentration of oxygen atoms on the
surface after polymerization, which is due to the PMMA brush.20
58
Figure 2.4. AFM topography 2D images (2.5 × 2.5 m): (a) 500 nm PS monolayer array,
(b) after electrodeposition of Cbz-Initiator and washing of PS microspheres (inverse
colloidal Cbz-Initiator arrays), and (c) after 1 hr polymerization of MMA. Line profile
analysis: (d) single PS microsphere, (e) cavity after electrodeposition of Cbz-Initiator and
PS removal, and (f) before and after SIP of MMA.
59
More compelling evidence about the growth of the polymer brush is given by the
attenuated total reflectance infrared (ATR-IR) analysis (Figure 2.5c), which shows the
characteristic peaks of PMMA.21
For example, when comparing the patterned film
(inverse colloidal Cbz-Initiator array) before (light grey) and after polymerization (gray),
an increase in the intensity of the peak at 1720 cm−1
due to the C=O stretching of the
ester groups is observed. In the case of the patterned film before polymerization, the
peak is mainly due to the ester linkage of the ATRP moiety.
After polymerization, the peak is due mainly to the ester in the PMMA brush.
The increase in peak intensity is expected since ATR-IR measurements are more
sensitive to the analysis of thicker films. Therefore the thicker PMMA brush will give a
greater sensitivity than that of the thinner non-polymerized film. A similar case of
increasing peak intensity is observed for both the -CH3, and -CH2, asymmetric stretching
at 2800–3000 cm−1
. It should also be mentioned that the -C=C- (1593 cm-1
) aromatic ring
peak of the macroinitiator film is no longer seen after the polymerization of MMA. This
disappearance of the aromatic ring peak can be attributed to the thick PMMA brush
coverage. Similarly, a comparison between the patterned and unpatterned (Figure 2.5c
black and dark grey curves respectively) PMMA surface revealed identical peaks with
different intensities. As expected, the peak intensities in the spectrum of the PMMA
brush grafted on the unpatterned ITO surface is higher than the PMMA patterned surface.
This increase in intensity can be attributed to the thicker brush formation in the
unpatterned surface.
60
Figure 2.5. High resolution XPS scan of the (a) C 1s (deconvoluted C 1s PMMA peak in
inset) and (b) the O 1s peak of the patterned film before and after polymerization of
MMA. (c) ATR-IR spectra of the inverse colloidal Cbz-Initiator arrays, PMMA brush on
patterned surface, and PMMA brush on unpatterned surface.
61
2.2.3. Formation of Inverse Colloidal Cbz-CTA and Cbz-Nb Arrays
Furthermore, by using the same chronoamperometric conditions as the Cbz-
Initiator, similar inverse colloidal patterns could be obtained for the Cbz-CTA and Cbz-
Nb Figure 2.6a and b respectively. Once again in combination with the AFM
topography images, high resolution XPS scans were performed to further prove the
presence of the Cbz-CTA on the surface. From the XPS scans, the Cbz-CTA displayed
the expected elemental signals of the C, N, O, and S film.1f
The appearance of the broad
signal at 163.5 eV in the S 2p region was attributed to the dithio-moiety of the CTA.22
With the successful patterning of the Cbz-CTA and Cbz-Nb, SI-RAFT
polymerization and ROMP were performed on the films using styrene and Nb monomers
respectively. In both cases AFM topography images (Figure 2.6c and d), line profiles
(Figure 2.7a and b), and high resolution XPS scans (Figure 2.7c and d) of the Cbz-CTA
and Cbz-Nb before and after SIP. For example, in the case of SI-RAFT polymerization of
styrene from the inverse colloidal Cbz-CTA arrays, AFM topography images depict a
clear morphological change when comparing before (Figure 2.6a) and after
polymerization (Figure 2.6c). Similar morphological changes are evident when
comparing the inverse colloidal Cbz-Nb arrays before (Figure 2.6b) and after SIP of Nb
monomer (Figure 2.6d) as well. Line profile analysis of the respective images before and
after SIP reveal an increase in the SI-RAFT polymerization film thickness of 11.3 ± 0.8
to 37.1 ± 2.7 nm (Figure 2.7a) and that of the SI-ROMP film (Figure 2.7b) of 10.4 ± 0.5
to 15.6 ± 1.1 nm, further indicating successful formation of PS and Nb brush
respectively. Finally, high resolution XPS scans of the C 1s peaks before and after SI-
62
polymerization also confirm the successful brush formation in both cases. For example,
as seen in Figure 2.7c and d, an increase in the intensity of the C 1s peaks is evident in
both the PS and polynorbornene brush systems. This increase in intensity can be
attributed to a higher concentration of carbon on both of the brush surfaces.
Figure 2.6. AFM topography 2D images (2.5 × 2.5 m): (a) the inverse colloidal Cbz-
CTA, (b) Cbz-Nb arrays, (c) Cbz-CTA after SIP of styrene (1 hr long polymerization
time), and (d) Nb from the Cbz-Nb inverse colloidal arrays (0.5 hr long polymerization
time).
In the case of the SI-ROMP, it should be noted that the reaction was not
terminated with ethyl vinyl ether, meaning that the polynorbornene brushes should be
capped with the ruthenium (Ru) containing Grubb’s 1st generation catalyst.23
A closer
63
examination of the XPS scan (Figure 2.7d) confirms this even after rigorous washing
with dichloromethane. For example, both the Ru 3d5/2 and the Ru 3p peaks (inset) are
evident.24
This characteristic peak of metathesis polymerization is indicative of “living
polymerization” meaning that a different monomer can now theoretically be polymerized
from the activated Nb macroinitiator to form block-copolymer brushes.23
Figure 2.7. AFM line profiles before and after polymerization: (a) styrene from the Cbz-
CTA and (b) Nb from the Cbz-Nb inverse colloidal arrays. High resolution XPS scans of
the C 1s peaks before and after polymerization of (c) styrene from the Cbz-CTA and (d)
Nb from the Cbz-Nb inverse colloidal arrays.
64
2.2.4. Patterned Binary Brush Surface via ATRP and RAFT Polymerization
Based on these results, it is clear that a variety of living/controlled polymerization
techniques (ATRP, RAFT, and ROMP) can be combined with colloidal templating to
form patterned polymer brush surfaces. It should be mentioned however, only a limited
number of routes to laterally patterned binary polymer brushes have been reported to
date. For example, Kang et al. used self-assembled monolayers (SAMs) containing
patterns of different initiators, followed by sequential, orthogonal polymerization steps.25
Another example of laterally patterned binary brush systems have been done by Rühe and
coworkers. Here, they used photoinitiated free-radical polymerization from successively
irradiated areas to create binary brush surfaces.26
Other examples include the works done
by Zhou et al. who prepared binary brushes via photoetching and reinitiation, and
Luzinov et al. who reported the use of an imprinted masking layer to form binary
brushes.27,28
Based on the need to create such films, it should be evident that we too could
produce such laterally patterned binary brush systems using a simpler approach combing
colloidal templating and electroactive initiators.
Recently our group has shown a method of creating topologically and chemically
defined polymer surfaces by combining colloidal templating and SIP from 11-(2-Bromo-
2-methyl)propionyloxy) undecyltrichlorosilane (ATRP-silane initiator) that was self
assembled in the cavities of the collodially templated surface.29
Based on these results, a
combined approach using the electroactive Cbz-CTA and the ATRP-silane initiator to
create laterally patterned binary brush surfaces was performed.
65
Figure 2.8. (a) Fabrication of the binary brush system via a combination of SI-RAFT
polymerization from the inverse colloidal Cbz-CTA and the SIP via ATRP from the
ATRP-silane initiator immobilized in the cavities of the pattern. AFM topography 2D
images (2.5 × 2.5 m): (b) inverse colloidal Cbz-CTA after back filling cavities with
ATRP-silane initiator, (c) after SIP of styrene from the colloidal Cbz-CTA with
backfilled cavities, and (d) after SIP of MMA from the ATRP-silane initiator.
The fabrication of the laterally patterned binary brush surfaces is illustrated in
Figure 2.8a. The first step involved back-filling of the cavities created after formation of
the inverse colloidal Cbz-CTA arrays (formed as mentioned earlier) with the ATRP-
silane initiator. This step was then followed by SI-RAFT polymerization of styrene
monomer (30 min reaction time) from the Cbz-CTA macrointiator. Subsequent SI-ATRP
66
Figure 2.9. (a) High resolution XPS scan of the signature Br 3d peak of the ATRP-silane
initiator. Line profiles at the various stages of film fabrication (b) from before and after
after backfilling cavities with ATRP-silane initiator, and (c) after SIP of styrene from the
colloidal Cbz-CTA with backfilled cavities with ATRP-silane initiator and after SIP of
MMA from the ATRP-silane initiator.
67
of MMA monomer (1 hr reaction time) was then performed to complete the binary brush
surface. AFM topography images confirm the success of the various stages of film
development. For example, the adsorption of the ATRP-silane initiator SAM into the
inner holes is clearly seen in the AFM topography image (Figure 2.8b). Changes in
surface morphology are also evident after SI-RAFT of styrene (Figure 2.8c) and SI-
ATRP of MMA (Figure 2.8d).
XPS and AFM line profile analyses were also used to characterize film
development. For example, the high resolution XPS scans reveal the presence of the Br
3d signature peak of the ATRP-silane initiator (Figure 2.9a) after back-filling the inverse
colloidal Cbz-CTA arrays.29
Similarly, the successful growth of the PS via RAFT
polymerization and PMMA via ATRP were also characterized via XPS scans of the C 1s
peak.1f
Further verification of the immobilization of the ATRP-silane initiator can be
seen in the decrease of the peak-to-baseline height in the AFM line profile analysis
(Figure 2.9b). The difference in height before and after ATRP-silane initiator
immobilization (∼2.2 nm) into the cavities is equivalent to the theoretical length of the
molecule from previous studies.30
The AFM line profile analysis provides further
evidence of the successful PS and PMMA brush formation (Figure 2.9c). For example,
by comparing Figure 2.9b and c after polymerization of PS, a clear increase in thickness
from 11.2 ± 0.3 nm to 19.0 ± 1.3 nm is evident. AFM line profile of the films after SI-
ATRP of MMA also reveals an increase in the peak-to-baseline height (16.8 ± 2.7 nm).
68
Based on these results it should be clear that any number of binary brush systems
could be fabricated. For example, herein ATRP and RAFT polymerization were reported,
however any previously reported polymerizable silane compound could be used i.e.
surface initiated nitroxide mediated polymerization (NMP), ROMP, RAFT
polymerization, or free radical polymerization.31-34
These techniques in combination with
the three types of electroactive initiators (Cbz-Initiator, Cbz-CTA, Cbz-Nb) shown
herein, ultimately display the actual versatility of this methodology.
2.3. Conclusions
In conclusion, a facile approach of creating topologically and well-defined
patterned polymer brushes by combining the techniques of 2D colloidal sphere
templating, electrodeposition of a macroinitiator, and SIP via ATRP, RAFT
polymerization, and ROMP was demonstrated. In the future, it should be possible to
focus on both the formation of more complex polymer brush systems (block copolymers,
mixed brushes, etc.) and the electro-optical properties of the underlying conjugated
polymer and CPN films. Another area for exploitation is the surface and electrochemistry
of the open (circle) ITO electrode array area. Applications are being targeted for dual
responsive sensors, wetting properties, and the tethering of biological receptors on the
open ITO electrode array area.
69
2.4. Experimental
2.4.1 Materials
Reagent chemicals SDS, MMA, (99%), Nb (99%), styrene (99%),
tetrabutylammonium hexafluorophosphate (TBAH, 99%), CuBr (99%), 2,2’-
azobisisobutyronitile (AIBN, 98%), triethylamine (TEA, 99%), and Grubb’s 1st
generation catalyst were purchased from Aldrich and were used without further
purification unless otherwise indicated. Chemicals N,N'-dicyclohexylcarbodiimide (DCC,
99%), 4-dimethylaminopyridine (DMAP, 99%), 18-crown-6, lithium aluminium
hydride, carbazole (99%), 1,4 dibromobutane (99%), 5-norbornene-2-methanol (99%),
sodium hydroxide, and methyl-3,5-dihydroxybenzoate (99%) were all purchased from
Alfa Aesar and were used without further purification. 2-bromoisobutyryl bromide (99%)
was purchased from Tokyo Chemical Industry and also used without any purification.
The PS latex microbeads (500 nm sizes, 2.5 wt% solids in aqueous suspension) were
purchased from Polysciences, Inc. and used without further purification. MMA and
styrene monomers containing inhibitor were passed through a column with alternating
layers of activated basic alumina and inhibitor remover replacement packing to remove
the inhibitor and were stored at -20 °C.
2.4.2. Instrumentation
Nuclear magnetic resonance (NMR) spectra were recorded on a General Electric
QE-500 spectrometer operating at 500 MHz for 1H NMR. The UV-vis spectrum was
recorded on a HP-8453 UV-vis spectrometer in the range between 300 to 800 nm. The
70
electropolymerized film on ITO was directly scanned onto the spectrometer with ITO
used as a blank. The films were completely dried under vacuum prior to the UV-vis
measurements. XPS was done using a PHI 5700 X-ray photoelectron spectrometer was
equipped with a monochromatic Al KR X-ray source (hν = 1486.7 eV) incident at 90o,
relative to the axis of a hemispherical energy analyzer. The spectrometer was operated
both at high and low resolutions with pass energies of 23.5 and 187.85 eV, respectively, a
photoelectron take off angle of 45o from the surface, and an analyzer spot diameter of 1.1
mm. All spectra were collected at room temperature with a base pressure of 1 X 10-8
Torr. The peaks were analyzed first by background subtraction, using the Shirley routine.
All the samples were completely dried in argon gas prior to XPS measurements. AFM
measurements were carried out in a piezo scanner from Agilent Technologies. The
scanning rate was set between 0.8 to 1.0 lines/s. Commercially available tapping mode
tips (TAP300, Silicon AFM Probes, Ted Pella, Inc.) were used on cantilevers with a
resonance frequency in the range of 290-410 kHz was performed. The scanning of the
electropolymerized films were performed under ambient and dry conditions. All AFM
topographic images (AAC tapping mode) were filtered and analyzed using SPIP
(Scanning Probe Image Processor, Imagemet.com) or Gwyddion 2.19 software. Cyclic
voltammetry was performed in a conventional three-electrode cell, using an Autolab
PGSTAT 12 potentiostat (Brinkmann Instruments (now MetroOhm USA)). The
potentiostat was controlled using GPES software (version 4.9). The deionized water (18.2
MΩcm) used for the dilution of PS particles was purified by a Milli-Q Academic system
(Millipore Corporation) with a 0.22 μm Millistack filter at the outlet. The ATR-IR spectra
71
were obtained on a Digilab FTS 7000 equipped with a HgCdTe detector from 4000 to
600 (cm-1
) wavenumbers. All spectra were taken with a nominal spectral resolution of 4
cm-1
in absorbance mode. All films were measured under ambient and dry conditions.
2.4.3. Surface Preparation
ITO substrates were first cut into 2.5 × 0.7 cm slides. The slides were then
cleaned using an Alconix solution followed by sonicating in isopropanol, followed by
hexanes, and toluene for 10 min each. The slides were then dried using N2 gas followed
by plasma cleaning for 3 minutes. The slides were either used immediately or stored in a
desiccator.
2.4.4. PS Monolayer Formation and Removal
The PS solution used for layering contained 1 wt% PS particles and 34.7 mM
SDS (spreading agent) in Milli-Q water. Prior to PS layering on indium tin oxide (ITO)
substrates, the solution was sonicated for 30 min. The layering of PS microbeads was
accomplished using a similar procedure described earlier by Grady and co-workers.18
The
method was called the LB-like technique because it formed a monolayer of PS particles
onto flat surfaces without using the conventional LB setup that employs floating barriers.
The substrate was attached into the dipper motor via a Teflon clip and was dipped into an
aqueous solution containing PS particles (1 wt %) and SDS (34.7 mM) as a spreading
agent. The substrate then was withdrawn vertically from the solution at a rate of 0.1-0.3
mm/min. Finally, the substrate was dried by suspending it in air for a few minutes. The
PS microspheres were removed from the surface after electropolymerization by dipping
72
the PS-coated substrate in THF twice for 30 min. This is done to create the inverse
colloidal crystals of conducting polymer pores and arrays (also called inverse opals or
PS-templated film). The substrate then was allowed to dry naturally under ambient
conditions.
The electropolymerization of the monomer was done using chronoamperometry
using an Autolab PGSTAT 12 potentiostat (Metro Ohm) in a standard three-electrode
measuring cell with platinum wire as the counter electrode, Ag/AgCl wire as the
reference electrode, and the bare ITO or PS-coated ITO substrate as the working
electrode. The potential was a constant 1.3 V for 3 min. After the electrodeposition, the
resulting film was washed with ACN thrice, and a monomer free scan was performed,
using a range of 0-1.3 V at 50 mV/s scan rate but for only one CV cycle. The
electropolymerized substrate was dried with nitrogen gas.
2.4.5. Surface-initiated ATRP
The ITO substrate with the PS patterned macroinitiator was placed into a Schlenk
flask charged with 4.6 mg (0.03 mmol) of CuBr and 9.36 mg (0.06 mmol) of 2,2’-
bipyridine (bpy) under a N2 atmosphere. A second Schlenk flask was charged with 300
mg (3 mmol) of MMA dissolved in 4 mL of water and 4 mL of methanol. Alternatively,
the substrate was placed in a 3rd Schlenk flask under a N2 atmosphere. The monomer
solutions were degassed using a nitrogen purge for a period of 30-45 min and then
transferred to the 3rd Schlenk flask under a N2 atmosphere. To remove any physically
73
adsorbed polymer from the substrates the polymerized slide was placed into a H2O,
MeOH solution overnight.
2.4.6. Surface-initiated RAFT Polymerization
In a typical run, a solution of styrene 300 mg (2.88 mmol), AIBN 0.20 mg
(0.0012 mmol), and 10 mL of dry THF were degassed in a Schlenck tube by bubbling
with N2 gas for 30-45 min. The degassed solutions were transferred to another Schlenck
tube backfilled with N2 gas containing the Cbz-CTA modified ITO through a cannula.
The tubes were placed in a preheated oil bath at 60 °C. The slides were then soaked
overnight using THF as solvent to remove any unbound polymers.
2.4.7. Surface-initiated ROMP
In a typical run, the ITO PS-patterned slides were immersed in a solution
containing 82.3 mg (0.1 mmol) of Grubb’s 1st generation catalyst in 10 ml DCM for 1 hr.
The slide would then be rinsed with copious amounts of DCM and placed into a solution
of 188 mg (2.0 X 10-3
mmols) of Nb in 10 ml DCM.
2.4.8. Synthesis
All molecules in this chapter were prepared according to previous literature as seen in
appendix I of this thesis.1f
74
2.5. References
1. (a) Tu, H.; Heitzman, C. E.; Braun, P. V. Langmuir 2004, 20, 8313. (b) Alarcon, C.
H.; Farhan, T.; Osborne, V. L.; Huck, W. T. S.; Alexander, C. J. Mater. Chem.
2005, 15, 2089. (c) Mahajan, N.; Lu, R.; Wu, S. T. ; Fang, J. Langmuir 2005, 21,
3132. (e) Hammond, P. T. Adv. Mater. 2004, 16, 1271. (f) Foster, E. L.; Tria, M. C.
R.: Pernites, R. B.; Addison, S. J.; Advincula, R. C. Soft Matter 2012, 8, 353.
2. Ayres, N.; Cyrus, C. D.; Brittain, W. J. Langmuir 2007, 23, 3744.
3. Chen, X. Y.; Armes, S. P.; Greaves, S. J.; Watts, J. F. Langmuir 2004, 20, 587.
4. Chiefari, J.; Chong, Y. K.; Ercole, F.; Krstina, J.; Jeffery, J.; Le, T. P. T.;
Mayadunne, R. T. A.; Meijs, G. F.; Moad, C. L.; Moad, G.; Rizzardo, E.; Thang, S.
H. Macromolecules 1998, 31, 5559.
5. Buchmeiser, M. R. Chem. Rev. 2000, 100, 1565.
6. Del Campo, A.; Arzt, E. Chem. Rev. 2008, 108, 911.
7. (a) Jones, D. M.; Smith, J. R.; Huck, W. T. S.; Alexander, C. Adv. Mater. 2002, 14,
1130. (b) Paul, K. E.; Prentiss, M.; Whitesides, G. M. Adv. Funct. Mater. 2003, 13,
259.
8. Ahn, S. J.; Kaholek, M.; Lee, W. K.; LaMattina, B.; LaBean, T. H.; Zauscher, S.
Adv. Mater. 2004, 16, 2141.
9. Kaholek, M.; Lee, W. K.; LaMattina, B.; Caster, K. C.; Zauscher, S. Nano Lett.
2004, 4, 373.
10. Werne, T. A. V.; Germack, D. S.; Hagberg, E. C.; Sheares, V. V.; Hawker, C. J.;
Carter, K. R. J. Am. Chem. Soc. 2003, 125, 3831.
75
11. (a) Martin, C. R.; Science 1994, 266, 1961. (b) Yuan, Z. H.; Huang, H.; Dang, H.
Y.; Cao, J. E.; Hu, B. H.; Fan, S. Appl. Phys. Lett. 2001, 78, 3127. (c) Rahman, S.;
Yang, H. Nano Lett. 2003, 3, 439.
12. (a) Park, M.; Harrison, C.; Chaikin, P. M.; Register, R. A.; Adamson, D. H.
Science 1997, 276, 1401. (b) Morey, M. S.; O’Brien, S.; Schwarz, S.; Stucky, G. D.
Chem. Mater. 2000, 12, 898. (c) Cheng, W.; Baudrin, E.; Dunn, B.; Zink, J. I. J.
Mater. Chem. 2001, 11, 92.
13. (a) Holland, B. T.; Blanford, C. F.; Stein, A. Science 1998, 281, 538. (b) Jiang, P.;
Bertone, J. F.; Colvin, V. L. Science 2001, 291, 453. (c) Norell, M. A.; Makovicky,
P.; Clark, J. M. Nature 1997, 389, 447.
14. (a) Velev, O. D.; Tessier, P. M.; Lenhoff, A. M.; Kaler, E. W. Nature 1999, 401,
548. (b) Jiang, P.; Cizeron, J.; Bertone, J. F.; Colvin, V. L. J. Am. Chem. Soc. 1999,
121, 7957.
15. Zakhidov, A. A.; Baughman, R. H.; IqbaL, Z.; Cui, C.; Khayrullin, I.; Dantas, S. O.;
Marti, J.; Ralchenko, V. G. Science 1998, 282, 897.
16. Deutsch, M.; Vlasov, Y. A.; Norris, D. J. Adv. Mater. 2000, 12, 1176.
17. Kaewtong, C.; Jiang, C. G.; Park, Y.; Fulghum, T.; Baba, A.; Pulpoka, B.;
Advincula, R. C. Chem. Mater. 2008, 20, 4915.
18. Marquez, M.; Grady, B. P. Langmuir 2004, 20, 10998.
19. Fulghum, T.; Karim, A.; Baba, A.; Taranekar, P.; Nakai, T.; Masuda, T.; Advincula,
R. Macromolecules 2006, 39, 1467.
20. Louetta, P.; Bodino, F.; Pireaux, J. J. Surf. Sci. Spectra 2005, 12, 69.
76
21. Kong, X.; Kawai, T.; Abe, J.; Iyoda, T. Macromolecules 2001, 34, 1837.
22. Morf, P.; Raimondi, F.; Nothofer, H.; Schnyder, B.; Yasuda, A.; Wessels, J.; Jung,
T. Langmuir 2006, 22, 658.
23. Binder, W. H.; Pulamagatta, B.; Kir, O.; Kurzhals, S.; Barqawi, H.; Tanner, S.
Macromolecules 2009, 42, 9457.
24. Varughese, B.; Chellamma, S.; Lieberman, M. Langmuir 2002, 18, 7964.
25. Xu, F. J.; Song, Y.; Cheng, Z. P.; Zhu, X. L.; Zhu, C. X.; Kang, E. T.; Neoh, K. G.
Macromolecules 2005, 38, 6254.
26. Prucker, O.; Habicht, J.; Park, I. J.; Rühe, J. Mater. Sci. Eng. C. 1999, 8, 291.
27. Zhou, F.; Jiang, L.; Liu, W. M.; Xue, Q. Macromol. Rapid Commun. 2004, 25,
1979.
28. Liu, Y.; Klep, V.; Luzinov, I. J. Am. Chem. Soc. 2006, 128, 8106.
29. Pernites, R. B.; Foster. E. L.; Felipe, M. J. L.; Robinson, M.; Advincula, R. C. Adv.
Mater. 2011, 23, 1287.
30. Yu. K.; Wang, H.; Xue, L.; Han, Y. Langmuir 2007, 23, 1443.
31. Husseman, M.; Malmström, E. E.; McNamara, M; Mate, M.; Mecerreyes, D.;
Benoit, D. G.; Hedrick, J. L.; Mansky, P.; Huang, E.; Russell, T. P.; Hawker, C. J.
Macromolecules 1999, 32, 1424.
32. Edmondson, S.; Osborne, V. L.; Huck, W. T. S. Chem. Soc. Rev. 2004, 33, 14.
33. Li, C. Z.; Benicewicz, B. C. Macromolecules 2005, 38, 5929.
34. Fulghum, T. M.; Taranekar, P.; Advincula, R. C. Macromolecules 2008, 41, 5681.
77
Chapter 3: Click Chemistry and Electro-grafting onto Colloidally
Templated Conducting Polymer Arrays
3.1. Introduction
Covalent tethering or chemical adsorption of macromolecules is a robust approach
to fine-tune surface and interfacial properties.1-3
Although somewhat limited in terms of
thickness and grafting density, a primary advantage of the “grafting to” polymer brush
approach is the ability to fully characterize the preformed polymer precursors prior to
adsorption. To date, the majority of research regarding the covalent tethering of polymers
to substrates has been based on the condensation of silane terminated linear polymers on
hydroxyl functionalized surfaces.4-7
Other novel techniques have been reported to tether
macromolecules. For example, Patton et al. described a series of well-defined dendritic-
linear copolymer architectures prepared via the reversible addition-fragmentation chain
transfer (RAFT) polymerization technique.8 Using dendritic chain transfer agents
(CTA)s, RAFT polymerization was carried out to polymerize linear polystyrene (PS) and
poly(methyl methacrylate) (PMMA) chains. These linear dendron polymers were then
successfully grafted electrochemically onto the conductive substrates via the electroactive
carbazole moieties at the periphery of the dendrons.
More recently, click chemistry has become a popular technique to covalently graft
prefabricated polymers to surfaces. The most widely used click reaction is the copper-
78
Figure 3.1. Structures of (a) prop-2-ynyl 3,5-bis(4-(9H-carbazol-9-yl)butoxy)benzoate
(Cbz-Alkyne), (b) 2-(2-(2-(2-hydroxy)ethoxy)ethoxy)ethyl-3(4-(9H-carbazol-9-
yl)butoxy)-5-(4-(9Hcarbazol-9yl)butoxy)) benzoate (Cbz-TEG), (c) electroactive
dendritic-linear PPEGMEMA (Cbz-PPEGMEMA-CTA) molecule, (d) linear PS with
terminal azide functional group (PS-N3) and, (e) linear PS with terminal alkyne
functional group (PS-Alkyne).
catalyzed azide alkyne cycloaddition (CuAAC) reaction.9 The CuAAC reaction is one
representative of a family of efficient chemical reactions, which are modular, widely
applicable, relatively insensitive to solvents, and pH ranges, while resulting in high
yields.10
This coupling reaction has been employed for the fabrication of grafted
poly(ethylene glycol) brushes onto alkyne-functionalized pseudobrushes and mucin-like
glycopolymers for microarray applications.11-12
79
An important complement to polymer brushes is nanopatterned polymeric
surfaces. Nanopatterned polymeric surfaces serve as excellent platforms for controlling
interfacial chemical interactions and biological component adsorption with applications
ranging from biomaterials and micro/nanofluidic systems to microelectromechanical
devices and photonic crystal materials.13
Due to this high interest, various strategies
including microcontact printing, photolithography, and electron beam (e-beam)
lithography have been developed for fabricating patterned polymer brushes.14
These
techniques however, require complex procedures or could only be applicable to specific
surfaces via patterned self-assembled monolayers (SAM). An underutilized technique for
the fabrication of two-dimensional (2D) surface patterning is the use of ordered colloidal
crystal templates. Porogenic templating has been done on ordered colloidal crystals that
serve as sacrificial templates (colloidal templating) for structuring inverse three-
dimensional (3D) colloidal arrays. Similarly, other sacrificial templates can come from a
variety of materials including anodized alumina, block copolymers, and inorganic or
organic colloidal spheres.15-17
Polymer colloidal spheres (PS microspheres) have drawn
particular attention due to the ease of handling, commercial availability, and their ability
to serve as sacrificial templates. Materials ranging from metals to glassy carbon have
been used to fill-in the interstitial void spaces in-between the ordered colloidal arrays.
However, the use of electroactive organic molecules and polymers is of high interest
because of their tunable electro-optical and electrochemical properties.17-20
Herein, the electrodeposition of a series of first-generation dendrons (Figure
3.1a-c) onto colloidally templated substrates is reported. The first part focuses on the
80
grafting of linear polystyrene molecules (Figure 3.1d and e) containing either an azide
(PS-N3) or terminal alkyne (PS-Alkyne) via the CuAAC reaction onto colloidally
templated conducting polymer arrays. Figure 3.2 demonstrates how the successful
grafting of the PS-N3 (Figure 3.2, Route 1) or PS-Alkyne (Figure 3.2, Route 2) was
achieved either through the use of the electroactive
Figure 3.2. Fabrication of highly ordered of colloidal arrays.
“clickable” molecule prop-2-ynyl 3,5-bis(4-(9H-carbazol-9-yl)butoxy)benzoate (Cbz-
Alkyne), or by backfilling an inverse colloidal 2-(2-(2-(2-hydroxy)ethoxy)ethoxy)ethyl-
3(4-(9H-carbazol-9-yl)butoxy)-5-(4-(9Hcarbazol-9yl)butoxy)) benzoate (Cbz-TEG) array
81
with azidoundecanethiol SAM, respectively. The second part of the paper examines an
alternative route (Figure 3.2, Route 3) for the direct grafting of electroactive linear
polymers via electrodeposition onto colloidally templated surfaces. This was achieved by
first polymerizing a linear poly((polyethylene glycol)3 methyl ether methacrylate)
(PPEGMEMA) from an electroactive RAFT polymerizable reagent i.e. 3,5-bis (4-(9H-
carbazol-9-yl) butoxy) benzyl 4-cyano-4 (phenylcarbonothioylthio) pentanoate (Cbz-
CTA). Following the electrodeposition of the electroactive linear PPEGMEMA (Cbz-
PPEGMEMA-CTA) and removal of the PS microspheres, novel temperature responsive
tuning of pore diameter was achieved.
3.2 Results and Discussions
3.2.1. Synthesis of PS-N3 and PS-Alkyne
The “grafting to” approach on colloidally templated surfaces relies on the
preparation of polymers having either a terminal azide (PS-N3) or alkyne (PS-Alkyne)
functional group that can react sequentially by CuAAC reaction. Atom transfer radical
polymerization (ATRP) was employed for controlled living radical polymerization to
enable monodispersed samples. The precursor PS-Br molecule was synthesized via
ATRP using styrene and methyl 2-bromo-2-methylpropionate (MBMP) along with CuBr/
N,N,N′,N′′,N′′-pentamethyldiethylenetriamine (PMDETA) as the catalyst system
(Scheme 3.1a). Using Gel permeation chromatography (GPC), the molecular weight
(Mn) and polydispersity index (PDI) of the PS-Br molecule was found to be 2,019 g/mol
and 1.017 respectively. A good correlation between GPC Mn and 1H NMR spectroscopy
82
(Mn = 1,997 g/mol) was also observed. To synthesize the PS-Alkyne another popular and
well-controlled living polymerization technique, RAFT polymerization, was used
(Scheme 3.1b). Here polymerization of styrene to yield PS-Alkyne was carried out in
toluene at 70 oC, yielding a rather low molar mass (Mn = 3,084 g/mol) and narrow PDI
(1.15). Once again, 1H NMR analysis data supported GPC data (Mn = 3,103 g/mol).
Scheme 3.1. Polymerization of Styrene via (a) ATRP and Post Nucleophilic Substitution,
(b) and RAFT Polymerization from 4-Cyano-4-(Thiobenzoylthio)Pentanoic Acid
In the case of the PS-Alkyne no further modification was required because the
“clickable” terminal alkyne was present after polymerization. In the case of the PS-Br
molecule additional steps were required to create the azido functional group necessary for
CuAAC. Nucleophilic substitution of the resulting Br end groups was achieved by
reaction with NaN3 in DMF at room temperature.23
1H NMR analysis (Figure 3.3) also
83
confirmed the conversion of PS-Br to PS-N3 due to the shift of the -terminal methine
from = 4.5 ppm (Ha) to = 3.9 ppm (Hb).21,24
Figure 3.3. 1H NMR spectra and peak labels for bromine-terminated polystyrene (PS-Br)
and, azido-terminated polystyrene (PS-N3).
3.2.2. Formation of Inverse Colloidal Cbz-Alkyne Arrays
The procedure for the formation of patterned polymer brush surfaces is illustrated
in Figure 3.2 (Route 1). First, PS microspheres (500 nm) immersed in a water sodium n-
dodecylsulphate (SDS) solution, were deposited onto a conducting ITO substrate using a
vertical motor via the Langmuir-Blodgett (LB)-like technique, forming a hexagonally
closed-packed monolayer.22
The colloidal pattern then becomes a mask for the in-situ
electrodeposition of an electroactive monomer to form an inverse opal of a conducting
polymer (polycarbazole). It should be mentioned that the use of a compatible solvent like
84
ACN is important to successfully electrodeposit electroactive molecules in order to
maintain the hexagonally closed-packed monolayer of PS microspheres. During
electrodeposition, solvents such as water, THF, DCM, or toluene tend to wash the
microspheres or destroy the order of the patterned surface.
Electrodeposition of Cbz-Alkyne was achieved via chronoamperometry using a
constant potential of 1.3 V for 3 min. To confirm the successful electrodeposition a
monomer-free scan was performed (Figure 3.4a). UV-Vis spectrum (Figure 3.4b) of the
Figure 3.4. (a) Representative I-T curve of the electrodeposition via chronoamperometry
at a constant potential of 1.3 V for 3 min and the subsequent monomer free scan (inset).
(b) UV-vis spectrum of inverse colloidal Cbz-Alkyne arrays after electrodeposition.
85
electrodeposited film after removal of the PS microspheres, by soaking in THF, reveals
the signature peaks of a typical cross-linked polycarbazole network film on ITO with
peaks centered at 430 and >750 nm. These peaks are assigned to the to ∗ transition of
the polycarbazole and the polaronic band formation of the conjugated polycarbazole and
their redox ion couple with the hexafluorophosphate ions respectively, further confirming
the successful formation of the inverse colloidal Cbz-Alkyne array.25,26
The advantage of using electrodeposition is that Cbz-Alkyne is only deposited at
the interstitial void spaces between the hexagonally packed PS microspheres (Figure
3.5a). The PS microspheres were then removed by washing with THF (2X, 30 min),
creating the 2D inverse colloidal Cbz-Alkyne arrays. AFM topography measurements of
the inverse colloidal Cbz-Alkyne arrays depict a high periodicity of the PS particle
imprinted film (Figure 3.5b). The size of the cavity matches the size of the PS particle
template as determined by the AFM line profile (Figure 3.5d and e). The AFM line
profile also showed that the average height of the cavity before polymerization was 9.2 ±
0.8 nm (Figure 3.5e and f).
3.2.3. Grafting of PS-N3 onto Inverse Colloidal Cbz-Alkyne Arrays
To create a highly ordered patterned grafted polymer film, the CuAAC reaction
was performed on the inverse colloidal Cbz-Alkyne arrays (Figure 3.5c). From the AFM
topography image the morphology has changed from the hexagonal array (Figure 3.5b),
to a relatively spherical void with a more granular appearance on the periphery of the
86
patterned area (Figure 3.5c). The AFM line profiles (Figure 3.5f) before and after
grafting PS-N3 also show an increase in the patterned film thickness from 9.2 ± 0.8 nm to
13.4 ± 1.8 nm.
Figure 3.5. AFM topography 2D images (4 × 4 m): (a) 500 nm PS particle monolayer
array, (b) after electrodeposition of Cbz-Alkyne and washing of PS microspheres
(inverse colloidal Cbz-Alkyne arrays), and (c) after grafting PS-N3. Line profile analysis
of (d) single PS particle, (e) cavities after electrodeposition of Cbz-Alkyne and PS
microspheres removal, and (f) Cbz-Alkyne arrays before and after CuAAC reaction with
PS-N3.
87
Further evidence of the successful grafting of PS-N3 via CuAAC reaction comes
from attenuated total reflectance infrared spectroscopy (ATR-IR). In Figure 3.6 an
increase in intensity of the characteristic peaks of PS is evident upon grafting the PS-N3
onto the Cbz-Alkyne arrays (grey) when compared to the ATR-IR spectra of the Cbz-
Alkyne film (black). For example, the ATR-IR spectrum of the grafted PS-N3 showed the
Figure 3.6. ATR-IR spectra of before and after grafting PS-N3 via CuAAC reaction to
the inverse colloidal Cbz-Alkyne array from (a) 1250 to 4000 cm-1
and 3100 to 3400 cm-
1 (inset).
expected peaks at 3034 cm-1
, 2932 cm-1
, 1600 cm-1
, 1500 cm-1
, and 1456 cm-1
corresponding to the aromatic C–H stretch, aliphatic C–H stretch of the polymer
backbone, two bands for C=C (in ring) stretches, and C–C aromatic stretch (in ring),
respectively.27
Also comparison of the PS-N3 grafted film to the Cbz-Alkyne reveals a
disappearance of the terminal alkyne signature peak at 3300 cm-1
(inset). This is
88
attributed to the formation of the triazole product upon grafting the PS-N3 to the Cbz-
Alkyne array.28
3.2.4. Formation of Inverse Colloidal Cbz-TEG Arrays
Another component of surface patterning is the fabrication of laterally patterned
binary polymer composites. It should be mentioned however that there are only a limited
number of ways to produce such surfaces.29
Recently our group has shown that laterally
patterned binary polymer surfaces can be produced via successive SIP from the
colloidally templated Cbz-CTA and SAM’s of 11-(2-Bromo-2-methyl)propionyloxy)
undecyltrichlorosilane (ATRP-silane initiator).30
Similarly successful colloidally
templated binary composites have also been fabricated from the inverse colloidal Cbz-
TEG arrays. From these arrays, the cavities were then backfilled with either a 1-
octadecanethiol or ATRP-silane initiator SAMs on gold (Au) or ITO substrates
respectively.31
Based on this it should also be possible to backfill the cavities with
“clickable” materials i.e. azidoundecanethiol .
The formation of the laterally patterned binary composite surface is illustrated in
Figure 3.2, Route 2. First the inverse colloidal Cbz-TEG polymer array was created on
Au substrates according to previous literature.31
The second step involved back-filling the
cavities of the inverse colloidal Cbz-TEG arrays with a “clickable” azidoundecanethiol.
This step was then followed by grafting PS-Alkyne to the azidoundecanethiol SAM’s via
CuAAC. AFM topography images (Figure 3.7a-c) and line profiles (Figure 3.7d-f),
confirms the success of the various stages of film development. For example, the
89
adsorption of azidoundecanethiol into the inner holes is clearly seen in the AFM
topography image (Figure 3.7b). Changes in surface morphology are also evident after
grafting the PS-Alkyne into the cavities of the Cbz-TEG arrays via the CuAAC reaction
(Figure 3.7c).
Figure 3.7. AFM topography 2D images (4 × 4 m): (a) inverse colloidal Cbz-TEG
array, (b) after back filling cavities with azidoundecanethiol , and (c) after grafting PS-
Alkyne via CuAAC reaction to azidoundecanethiol . Line profile analysis: (d) inverse
colloidal Cbz-TEG array, (e) after back filling cavities with azidoundecanethiol , and (f)
after grafting PS-Alkyne via CuAAC reaction to azidoundecanethiol .
Further verification of film development can be seen in the AFM line profiles in
Figure 3.7d-f. For example, the successful immobilization of the azidoundecanethiol
inside the cavities of Cbz-TEG arrays was determined by the difference in height before
(Figure 3.7d) and after immobilization of azidoundecanethiol (1.8 ± 0.4 nm). This value
90
is equivalent to the experimental length found in literature.32
The AFM line profile
analysis provides further evidence of the successful grafting of PS-Alkyne onto the
azidoundecanethiol SAM (Figure 3.7f). For example, by comparing Figure 3.7e and
Figure 3.7f, a clear increase in thickness from 1.8 ± 0.4 nm to 8.8 ± 1.3 nm is evident.
Figure 3.8. High resolution XPS scans of N 1s peaks before and after grafting PS-Alkyne
to azidoundecanethiol.
High-resolution X-ray photoelectron spectroscopy (XPS) spectra of the azide-
terminated SAM further established the presence of the azide functionality bond, and
provided a benchmark for comparison after the CuAAC (Figure 3.8). For example, the N
1s photoelectron spectrum shows two distinct peaks at 399.5 and 403.5 eV. The lower
binding energy (BE) peak (399.5 eV) is attributed to the electron-rich outer nitrogen(s) of
the azide and the higher BE peak (403.5 eV) to the electron deficient inner nitrogen.33-34
Comparing the N 1s spectrum on the surface before and after the CuAAC reaction of PS-
91
Alkyne, the azide peak at 404.5 eV was reduced significantly after the reaction (Figure
3.8). This indicates the conversion of azide groups to the triazole ring during the
cycloaddition reaction.35
Based on these results it should be clear that a number of possible binary systems
could be fabricated. For example, the CuAAC reaction of PS-N3 or PS-Alkyne onto
“clickable” colloidally templated surfaces was reported, however any previously reported
clickable arrays could also be theoretically covalently grafted to these surfaces. Examples
include biotin, proteins, carbohydrates, and nanomicrospheres.36
3.2.5. Temperature Responsive PPEGMEMA
Porous membranes that predictably respond to pH, temperature, or electric fields
have been the focus of research for the last few decades.37-39
These responsive
membranes presnt potential applications including controlled drug release, catalysis,
sensors and separation of macromolecules including biological molecules such as
proteins. One of the most widely used approaches to create membranes with controlled
porosity is to graft stimuli-responsive macromolecules onto the surfaces of porous
membranes. Recently, oligo(ethylene glycol)-methacrylic polymers have attracted
interest because of their biocompatibility and thermo-responsive properties.40
Based on the interest in porous membranes, a novel approach to combine the
“grafting to” approach of the electroactive and thermo-responsive Cbz-PPEGMEMA-
CTA and colloidal templating is also presented. Scheme 3.2 depicts the fabrication of
Cbz-PPEGMEMA-CTA from the Cbz-CTA and the subsequent thermo-responsive arrays
92
following electrodeposition and removal of the PS microspheres. Here polymerization of
PEGMEMA to yield Cbz-PPEGMEMA-CTA was carried out in THF at 70 oC, yielding
relatively high molar mass (Mn = 13,087 g/mol) and PDI (1.29).
Scheme 3.2. (a) Formation of Cbz-PPEGMEMA-CTA (b) and Thermo-responsive
Colloidal Cbz-PPEGMEMA-CTA Arrays
1H NMR analysis data shows the typical peaks of the PPEGMEMA further
confirming successful formation via RAFT polymerization (Figure 3.9a).41
As seen in
93
Figure 3.9b one can see from the zoomed in aromatic region of the 1H spectra that the
electroactive carbazole and the terminal CTA moieties are still present.8 End group
analysis to find molar mass (Mn = 12,900 g/mol) from the 1H spectra are also consistent
with GPC data.
Electrodeposition of Cbz-PPEGMEMA-CTA on colloidally templated ITO was
achieved via cyclic voltammetry (CV) using a scanning potential of 0-1.1 V for 20 cycles
at a scan rate of 100 mV/s (Figure 3.9c). In the first CV cycle, the oxidation peak has an
onset potential at ~1.0 V. This onset is attributed to the formation of electron in the
nitrogen atom of the N-substituted carbazole monomer.42
This reactive radical cation
combines with another radical cation to form the polycarbazole. In the second cycle, a
new oxidation peak appears between 0.7 V and 1.0 V due to the formation of a more
stable bipolaron with extended π-conjugation. The corresponding reduction peak in the
reverse scan, from 0.6 V to 0.9 V is also evident. As time progresses the current increases
at this reduction oxidation (redox) peak, indicating the formation of more -conjugated
species as a result of further cross-linking between the carbazole molecules and
electrodeposition of more Cbz-PPEGMEMA-CTA onto the ITO electrode substrate. UV-
Vis was used to further prove the presence of the Cbz-PPEGMEMA-CTA arrays.1b
Investigations into the swelling and collapsing nature of PPEGMEMA brushes
due to their lower critical solution temperature (LCST) transition have been thoroughly
examined.43
Herein, the thermo-responsive properties of the colloidally templated Cbz-
PPEGMEMA-CTA arrays were investigated by comparing the AFM topography images
94
at either 22 oC (Figure 3.10a) or 70
oC (Figure 3.10b). As can be seen in Figure 3.10a,
at 22 oC the water temperature is below the LCST of PPEGMEMA, leading to the
swollen morphology of the colloidal arrays. What can also be seen from the AFM
images is that the pores of the inverse colloidal arrays are partially covered by the
swollen polymer array. When the temperature is increased to 70 oC, a collapse of the
colloidal Cbz-PPEGMEMA-CTA array is evident,
Figure 3.9. 1H NMR spectra from (a) 0.6 ppm to 8.3 ppm (b) 6.8 ppm to 8.3 ppm. (c)
Cyclic voltammetry scan of the electrodeposition of Cbz-PPEGMEMA-CTA onto
colloidally templated ITO substrate.
95
leading to a progressive opening of the pores. This collapse can be attributed to the
thermo-responsive nature of PEGMEMA molecules. For example, hydrogels are exposed
to an aqueous solution at a temperature that is below their LCST, water polymer
interactions dominate and the hydrogel swells. Above the LCST however, hydrophobic
interactions between the polymer chains dominate and the hydrogel structure collapses,
releasing water from the hydrogel matrix.44
Similarly, peak-to-baseline AFM line profile
analysis (Figure 3.10c) was also performed in order to get more insight into the swelling
deswelling behavior. As seen from Figure 3.10c, a collapse is evident is the swollen case
(22 oC) where the baseline is no longer evident. This data means that the thermo-
responsive material fills in (less porous) the cavities of the hexagonally closed packed
arrays (note: in the peak-to-baseline AFM line profile analysis, swelling in the z-axis
(vertical swelling) was ignored). In the case when the temperature was above the LCST
(70 oC), the patterns return to a more familiar hexagonally closed pack array, and a
clearer baseline is also evident (Figure 3.10c)
Ion permeability studies were also performed using the colloidally templated Cbz-
PPEGMEMA-CTA arrays (Figure 3.10d). To test the effects of temperature on ion
permeability, Fe(CN6)3-
anions were used as molecular probes. After scanning at room
temperature (22 oC) the electrochemical cell was immersed in a preheated water bath at a
temperature of 70 °C, in order to maximize the collapse of the colloidally templated
PPEGMEMA array and hence increase its porosity. Comparison of the room temperature
and elevated temperature experiments indicated an increase in the maximum current
density by 20 % at the elevated temperature 70 °C. This is a consequence of the collapse
96
of the PPEGMEMA array which enhances the ion transport through the exposed ITO
surface. Temperature changes the permeability of the membrane primarily by limiting ion
transport. In principle, smart colloidal arrays can be designed to have temperature-
dependent properties with respect to ion- and electron- transport properties for practical
applications.
Figure 3.10. AFM topography images of the inverse colloidal Cbz-PPEGMEMA-CTA
arrays at (a) 22 oC and (b) 70
oC. (c) AFM line profiles of the inverse colloidal Cbz-
PPEGMEMA-CTA arrays at 22 oC and 70
oC (d) Cyclic voltammetry comparative scan
of inverse colloidal Cbz-PPEGMEMA-CTA arrays at 22 oC and 70
oC.
97
3.3 Conclusions
In conclusion, new approaches of creating topologically and well-defined
“clickable” colloidally templated arrays: the grafting chemistry can be performed onto an
electrodeposited pattern or by subsequent backfilling with azido terminated SAM’s on
templated conducting polymer arrays was demonstrated. Another approach enabled the
fabrication of ion gates by electrografting colloidally templated electroactive thermo-
responsive oligo(ethylene glycol)-methacrylic polymers. Future work will focus on the
incorporation of binary biological arrays, e.g. controlled or tunable absorption of various
molecules into the templated Cbz-PPEGMEMA-CTA cavities with proteins or other
biological macromolecules.
3.4. Experimental section
3.4.1. Materials
Reagent chemicals SDS, styrene (99%), tetrabutylammonium
hexafluorophosphate (TBAH, 99%), CuBr (99%), 2,2’-azobisisobutyronitile (AIBN,
99%), and triethylamine (TEA, 99%), were purchased from Aldrich and were used
without further purification unless otherwise indicated. Chemicals N,N'-
dicyclohexylcarbodiimide (DCC, 99%), 4-dimethylaminopyridine (DMAP, 99%),
PEGMEMA, PMDETA, potassium thioacetate, sodium azide, 18-crown-6, lithium
aluminium hydride, carbazole (99%), 1,4 dibromobutane (99%), MBMP, tetraethylene
glycol (99%), 4-cyano-4-(thiobenzoylthio)pentanoic acid, sodium hydroxide, and methyl-
3,5-dihydroxybenzoate (99%) were all purchased from Alfa Aesar and were used
98
without further purification. 2-bromoisobutyryl bromide (99%) was purchased from
Tokyo Chemical Industry (TCI) and also used without any purification. The Polystyrene
(PS) latex microspheres (500 nm sizes, 2.5 wt% solids in aqueous suspension) were
purchased from Polysciences, Inc. and used without further purification. Deionized water,
methanol (MeOH), dicholoromethane (DCM), dimethylformamide (DMF), acetonitrile
(ACN), and tetrahydrofuran (THF) were used in the formation of patterned ITO or Au
slides, synthesis, and polymerization reactions. Styrene and PEGMEMA monomers
containing inhibitor were passed through a column with alternating layers of activated
basic alumina and inhibitor remover and were stored at -20 °C.
3.4.2. Polymerization of Styrene to Form of PS-Br
The polymerizations of styrene were conducted with conditions modified from
previously reported methods.21
For all polymerizations, oxygen was removed by three
freeze-pump-thaw cycles followed by backfilling with nitrogen. Linear PS-Br was
prepared by atom transfer radical polymerization (ATRP)
([Sty]/[MBMP]/[CuBr]/[PMDETA]) 100:1:1:1, 40 vol % toluene, 80 °C). The
polymerization was stopped after 3 hr by exposing the reaction mixture to air. The
mixture was diluted with THF and passed through a neutral alumina column to remove
the copper. The polymer was then reprecipitated in MeOH (3X) and dried.
3.4.3. Synthesis of PS-N3
The PS-Br (0.05 M) molecules were reacted with NaN3 (1.1 equiv) at room temperature
in DMF to yield PS-N3. The polymers were isolated by precipitation into MeOH.
99
3.4.4. Synthesis of CTA-Alkyne
In a one-necked flask, 4-cyano-4-(thiobenzoylthio)pentanoic acid (500 mg, 1.8
mmol), propargyl alcohol (201 mg, 3.6 mmol), and DMAP (22 mg, 0.18 mmol) were
combined. The mixture was dissolved in 50 ml of DCM, bubbled with nitrogen, and
placed in an ice bath. After which, a solution of DCC (743 mg, 3.6 mmol) in DCM was
added dropwise to the reaction mixture. This was then stirred vigorously for 30 mins,
warmed to room temperature and stirred overnight. The solid by-product was filtered off
and the filtrate was washed with water (2x) and brine solution (2x). The mixture was then
subjected to column chromatography using 1/4 hexanes/DCM.
3.4.5. Polymerization of Styrene to Form of PS-Alkyne
PS-Alkyne was prepared by RAFT ([Sty]/[AIBN]/[CTA-Alkyne]) 600:1:5, 50 vol
% toluene) polymerization. The solution was subjected to 3 freeze-pump-thaw cycles
followed by backfilling with nitrogen. The solution was heated at 70 oC for 5 hr.
Afterwards the solution was cooled to room temperature and the solvent was minimized.
The solution was then reprecipitated in MeOH (3X) and dried.
3.4.6. Synthesis of Cbz-CTA
The synthesis of Cbz-CTA was performed according to literature.8
3.4.7. Polymerization of PEGMEMA to Form Cbz-PPEGMEMA-CTA
Cbz-PPEGMEMA-CTA was prepared by RAFT ([PEGMEMA]/[AIBN]/[Cbz-
CTA]) 600:1:5, 50 vol % dry THF). The solution was subjected to 3 freeze-pump-thaw
100
cycles followed by backfilling with nitrogen. The solution was heated at 70 oC for 24 hr.
Afterwards, the solution was cooled to room temperature and the solvent was minimized.
The solution was then reprecipitated in hexane (3X) and dried.
3.4.8. Surface Preparation and Electrodeposition
The solution used for layering, contained 1 wt % PS microspheres and 34.7 mM
SDS (spreading agent) in Milli-Q water. The layering of PS microspheres was
accomplished using a procedure described by Grady and co-workers.22
The method is
called the LB-like technique because it forms a monolayer of PS microspheres onto flat
surfaces without using the conventional LB setup that employs floating barriers. The
substrate was attached into the dipper motor via a Teflon clip and was dipped into an
aqueous solution containing PS microspheres (1 wt %) and SDS (34.7 mM). The
substrate was withdrawn vertically from the solution at a rate of 0.3 mm/min. Finally, the
substrate was dried by suspending it in air for a few minutes. The PS microspheres were
removed from the surface after electropolymerization by dipping the PS microsphere
coated substrate in THF twice for 30 min. This is done to create the inverse colloidal
crystals of conducting polymer pores and arrays (also called inverse opals or PS-
templated film). The substrate then was allowed to dry naturally under ambient
conditions.
The electropolymerization of the monomer was done using both
chronoamperometry and cyclic voltammetry (CV) using an Autolab PGSTAT 12
potentiostat (Metro Ohm) in a standard three-electrode measuring cell, a fabricated
101
electrochemical cell with a diameter of 1.0 cm and volume of 0.785 cm3, made of
Teflon) with platinum wire as the counter electrode, Ag/AgCl wire as the reference
electrode, and PS microsphere coated Au or ITO substrates as the working electrode. For
CV, a potential of 0-1.1 V, scan rate 50 mV/s or 100 mV/s, and 20 cycles was used. For
chronoamperometry, the potential was kept constant at 1.3 V for 3 min. After the
electrodeposition, the resulting film was washed with ACN thrice, and a monomer free
scan was performed, using a range of 0-1.3 V at 50 mV/s scan rate but for only one CV
cycle. The electropolymerized substrate was dried with nitrogen gas.
The inverse colloidal Cbz-PPEGMEMA-CTA arrayed ITO substrates were
immersed in the solution at room temperature for 60 min prior to CV. For the elevated
temperature scans, the electrochemical cell was placed in a temperature-controlled water
bath at 70 °C for 60 min prior to electrochemical testing.
3.4.9. Copper-catalyzed Click Reactions
In a typical experiment, a solution of PS-N3 or PS-Alkyne (0.1 M) was dissolved
in DMF. Afterwards PMDETA (0.5 equiv) was added and the solution was degassed.
After degassing, the solution was transferred to a second degassed Schlenk tube
containing CuBr (0.5 equiv), and the substrates containing either the colloidally
templated Cbz-Alkyne arrays or the azidoundecanethiol films. The reactions were
allowed to go for 24 hr. Afterwards the substrates were removed and rinsed with DMF,
water, and MeOH followed by drying under vacuum before characterization.
102
3.4.10 Synthesis of Electroactive Monomers and 9-azidononane-1-thiol
Electroactive monomers and 9-azidononane-1-thiol were prepared according to literature
as demonstrated in appendix II.1b
3.4.11. Characterization
Nuclear magnetic resonance (NMR) spectra were recorded on a General Electric
QE-500 spectrometer operating at 500 MHz for 1H NMR. The UV spectrum was
recorded on a HP-8453 UV-Vis spectrometer in the range between 300 to 800 nm. The
electropolymerized film on ITO was directly scanned onto the spectrometer with ITO
used as a blank. The films were completely dried under vacuum prior to the UV-Vis
measurements. X-ray Photoelectron Spectroscopy (XPS) was done using a PHI 5700 X-
ray photoelectron spectrometer was equipped with a monochromatic Al KR X-ray source
(hν = 1486.7 eV) incident at 90o, relative to the axis of a hemispherical energy analyzer.
The spectrometer was operated both at high and low resolutions with pass energies of
23.5 and 187.85 eV, respectively, a photoelectron take off angle of 45o from the surface,
and an analyzer spot diameter of 1.1 mm. All spectra were collected at room temperature
with a base pressure of 1 X 10-8
Torr. The peaks were analyzed first by background
subtraction, using the Shirley routine. All the samples were completely dried in argon gas
prior to XPS measurements. Atomic Force Microscopy (AFM) measurements were
carried out in a piezo scanner from Agilent Technologies. The scanning rate was set
between 0.8 to 1.0 lines/s. Commercially available tapping mode tips (TAP300, Silicon
AFM Probes, Ted Pella, Inc.) were used on cantilevers with a resonance frequency in the
103
range of 290-410 kHz was performed. The scanning of the electropolymerized films were
performed under ambient and dry conditions. All AFM topographic images (AAC
tapping mode) were filtered and analyzed using SPIP (Scanning Probe Image Processor,
Imagemet.com) or Gwyddion 2.19 software. Cyclic voltammetry (CV) was performed in
a conventional three-electrode cell, using an Autolab PGSTAT 12 potentiostat
(Brinkmann Instruments (now MetroOhm USA)). The potentiostat was controlled using
GPES software (version 4.9). The deionized water (18.2 MΩcm) used for the dilution of
PS microspheres was purified by a Milli-Q Academic system (Millipore Corporation)
with a 0.22 μm Millistack filter at the outlet. The attenuated total reflectance fourier
transform infrared (ATR-FTIR) spectra were obtained on a Digilab FTS 7000 equipped
with a HgCdTe detector from 4000 to 600 (cm-1
) wavenumbers. All spectra were taken
with a nominal spectral resolution of 4 cm-1
in absorbance mode. All films were
measured under ambient and dry conditions.
3.5 References
1. (a) Advincula, R. C.; Brittain, W. J.; Caster, K. C.; Rühe, J. In Polymer Brushes:
Sythesis, Characterization, Applications; Wiley-VCH: Weinheim, 2004. (b) Foster,
E. L.; Bunha, A.; Advincula, R. Polymer 2012, 53, 3124.
2. Zhao, B.; Brittain, W. J. Prog. Polym. Sci. 2000, 25, 677.
3. Pyun, J.; Matyajaszewski, K.; Chem. Mater. 2001, 13, 3436.
4. Geoghegan, M.; Clarke, C. J.; Boue, F.; Menelle, A.; Russ, T.; Bucknall, D. G.
Macromolecules 1999, 32, 5106.
104
5. Yang, Z.; Galloway, J. A.; Yu, H. Langmuir 1999, 15, 8405.
6. Tran, Y.; Auroy, P. J. Am. Chem. Soc. 2001, 123, 3644.
7. Cecchet, F.; Meersman, B. D.; Demoustier-Champagne, S.; Nysten, B.; Jonas, A.
M. Langmuir 2006, 22, 1173.
8. Patton, L. D.; Taranekar, P.; Fulghum, T.; Advincula, R. Macromolecules 2008, 4,
6703.
9. Nandivada, N.; Chen, H. Y.; Bondarenko, L.; Lahann, J. Angew. Chem. Int. Ed.
2006, 45, 3360.
10. Kolb, H. C.; Finn, M. G.; Sharpless. K. B. Angew. Chem. Int. Ed. 2001, 40, 2004.
11. Ostaci, R. V.; Damiron, D.; Grohens, Y.; Légar, L.; Drockenmuller, E. Langmuir
2010, 26, 1304.
12. Godula, K.; Rabuka, D.; Nam, K. T.; Bertozzi, C. R. Angew. Chem. Int. Ed. 2009,
48, 4973.
13. (a) Xu, F. J.; Neoh, K. G.; Kang, E. T. Prog. Polym. Sci. 2009, 34, 19 (b) Nie, Z.;
Kumacheva, E. Nat. Mater. 2008, 7, 277. (c) Geissler, M.; Xia, Y. Adv. Mater.
2004, 16, 1249.
14. (a) Chen, T.; Chang, D. P.; Zauscher, S. Small 2010, 6, 1504. (b) Jones, D. M.;
Smith, J. R.; Huck, W. T. S.; Alexander, C. Adv. Mater. 2002, 14, 1130. (c)
Konradi, R.; Rühe, J. Langmuir 2006, 22, 8571. (d) Prucker, O.; Schimmel, M.;
Tovar, G.; Knoll, W.; Rühe, J. Adv. Mater. 1998, 10, 1073. (e) Zhou, F.; Jiang, L.;
Liu, W.; Xue, Q. Macromol. Rapid Commun. 2004, 25, 1979. (f) Rastogi, A.; Paik,
M.; Tanaka, M.; Ober, C. ACS Nano 2010, 4, 771. (g) Ahn, S. J.; Kaholek, M.; Lee,
105
W.; LaMattina, B.; LaBean, T.; Zauscher, S. Adv. Mater. 2004, 16, 2141. (h)
Brough, B.; Christman, K. L.; Wong, T. S.; Kolodziej, C. M.; Forbes, J. G.; Wang,
K.; Maynard, H. D.; Ho, C. M. Soft Matter 2007, 3, 541.
15. (a) Martin, C. R. Science 1994, 266, 1961. (b) Yuan, Z. H.; Huang, H.; Dang, H. Y.;
Cao, J. E.; Hu, B. H.; Fan, S. Appl. Phys. Lett. 2001, 78, 3127. (c) Rahman, S.;
Yang, H. Nano Lett. 2003, 3, 439.
16. (a) Park, M.; Harrison, C.; Chaikin, P. M.; Register, R. A.; Adamson, D. H. Science
1997, 276, 1401 (b) Morey, M. S.; O’Brien, S.; Schwarz, S.; Stucky, G. D. Chem.
Mater. 2000, 12, 898. (c) Cheng, W.; Baudrin, E.; Dunn, B.; Zink, J. I. J. J. Mater.
Chem. 2001, 11, 92.
17. (a) Holland, B. T.; Blanford, C. F.; Stein, A. Science 1998, 281, 538. (b) Jiang, P.;
Bertone, J. F.; Colvin, V. L. Science 2001, 291, 53. (c) Norell, M. A.; Makovicky,
P.; Clark, J. M. Nature 1997, 389, 447.
18. (a) Velev, O. D.; Tessier, P. M.; Lenhoff, A. M.; Kaler, E. W. Nature 1999, 401,
548. (b) Jiang, P.; Cizeron, J.; Bertone, J. F.; Colvin, V. L. J. Am. Chem. Soc. 1999,
121, 7957.
19. Zakhidov, A. A.; Baughman, R. H.; Iqbal, Z.; Cui, C.; Khayrullin, I.; Dantas, S. O.;
Marti, J.; Ralchenko, V. G. Science 1998, 282, 897.
20. Deutsch, M.; Vlasov, Y. A.; Norris, D. J. Adv. Mater. 2000, 12, 1176.
21. Vogt, A. P.; Sumerlin, B. S. Macromolecules 2006, 39, 5286.
22. Marquez, M.; Grady, B. P. Langmuir 2004, 20, 10998.
23. Coessens, V.; Pintauer, T.; Matyjaszewski, K. Prog. Polym. Sci. 2001, 26, 337.
106
24. Tsarevsky, N. V.; Sumerlin, B. S.; Matyjaszewski, K. Macromolecules 2005, 38,
3558.
25. Kaewtong, C.; Jiang, C. G.; Park, Y.; Fulghum, T.; Baba, A.; Pulpoka, B.;
Advincula, R. C. Chem. Mater. 2008, 20, 4915.
26. Fulghum, T.; Karim, A.; Baba, A.; Taranekar, P.; Nakai, T.; Masuda, T.; Advincula,
R. Macromolecules 2006, 39, 1467.
27. Tria, M. C.; Park, J. Y.; Advincula, R. Chem. Commun. 2011, 47, 2393.
28. Nandivada, H.; Chen, H.; Bondarenko, L.; Lahann, J. Angew. Chem. Int. Ed. 2006,
45, 3360.
29. Zhou, F.; Zheng, Z.; Yu, B.; Liu, W.; Huck, W. T. S. J. Am. Chem. Soc. 2006, 128,
16253.
30. Foster, L. E.; Tria, M. C. R.; Pernites, R. B.; Addison, S. J.; Advincula, R. C. Soft
Matter 2012, 8, 353.
31. (a) Pernites, R. B.; Felipe, M. J. L.; Foster, E. L.; Advincula, R. C. ACS Appl.
Mater. Interfaces 2011, 3, 817. (b) Pernites, R. B.; Foster, E. L.; Felipe, M. L.;
Robinson, M.; Advincula, R. C. Adv. Mater. 2011, 23, 1287.
32. Zirbs, R.; Kienberger, F.; Hinterdorfer, P.; Binder, W. H. Langmuir 2005, 21, 8414.
33. Tarlov, M. J.; Burgess, D. R. F.; Gillen, G. J. Am. Chem. Soc. 1993, 115, 5305.
34. Wollman, E. W.; Kang, D.; Frisbie, C. D.; Lorkovic, I. M.; Wrighton, M. S. J. Am.
Chem. Soc. 1994, 116, 4395.
35. Radhakrishnan, C.; Lo, M. K. F.; Warrier, M. V.; Garcia-Garibay, M. A.;
Monbouquette, H. G. Langmuir 2006, 22, 5018.
107
36. (a) Qin, G.; Santos, C.; Zhang, W.; Li, Y.; Kumar, A.; Erasquin, U. J.; Liu, K.;
Muradov, P.; Trautner, B. W.; Cai, C. J. Am. Chem. Soc. 2010, 132, 16432. (b)
Broyer, R. M.; Schopf, E.; Kolodziej, C. M.; Chen, Y.; Maynard, H. D. Soft Matter
2011, 7, 9972. (c) Zhang, Y.; Luo, S.; Tang, Y.; Yu, L.; Hou, K. –Y.; Cheng, J. –P.;
Zeng, X.; Wang, P. G. Anal. Chem. 2006, 78, 2001. (d) Gassensmith, J. J.; Erne, P.
M.; Paxton, W. F.; Valente, C.; Stoddart, J. F. Langmuir 2011, 27, 1341.
37. Lee, D.; Nolte, A. J.; Kunz, A. L.; Rubner, M. F.; Cohen, R. E. J. Am. Chem. Soc.
2006, 128, 8521.
38. Chu, L. Y.; Li, Y.; Zhu, J. H.; Chen, W. M. Angew. Chem. Int. Ed. 2005, 44, 2124.
39. Lee, S. B.; Martin, C. R. J. Am. Chem. Soc. 2002, 124, 11850.
40. (a) Jonas, A. M.; Hu, Z.; Glinel, K.; Huck, W. T. S. Nano Lett. 2008, 8, 3819. (b)
Yavus, M. S.; Buyukserin, F.; Zengin, Z.; Camli, S. T. J. Polym. Sci. Part A:
Polym. Chem. 2011, 49, 4800. (c) Tria, M. C. R.; Grande, C. D. T.; Ponnapati, R.
R.; Advincula, R. C. Biomacromolecules 2010, 11, 3422.
41. (a) Lutz, J. –F.; Börner, H. G.; Weichenhan, K. Macromolecules 2006, 39, 6376.
(b) Han, S.; Hagiwara, M.; Ishizone, T. Macromolecules 2003, 36, 8312.
42. (a) Ambrose, J. F.; Nelson, R. F. J. Electrochem. Soc. 1968, 115, 1159. (b) Xia, C.;
Advincula, R. C. Chem. Mater. 2001, 13, 1682.
43. (a) Li, D.; Jones, G. L.; Dunlap, J. R.; Hua, F.; Zhao, B. Langmuir 2006, 22, 3344.
(b) Boyer, C.; Whittaker, M. R.; Luzon, M.; Davis, T. P. Macromolecules 2009, 42,
6917.
108
44. Meenach, S. A.; Anderson, K. W.; Hilt, J. Z. J. Polym. Sci. Part A: Polym. Chem.
2010, 48, 3229.
109
Chapter 4: Electropolymerized and Polymer-grafted
Superhydrophobic, Superoleophilic, and Hemi-wicking Coatings
4.1. Introduction
Superhydrophobic surfaces have vital importance in naturally occurring systems,
e.g. lotus leaf, strider insect, and the eucalyptus plant. A common test for designating
superhydrophobic is when the water droplet on the surfaces has a contact angle (CA)
greater than 150o.1 Due to this high contact angle only 2-3 % of the water droplet comes
into contact with the surface. Mimicking the high water repellence of superhydrophobic
surfaces make them ideal candidates for industrial applications including self-cleaning,
biocorrosion inhibition, antifouling marine coatings, microfluidics, and anti-ice adhesion
systems.2 These properties have inspired the establishment of methodologies and
theoretical modeling on how to obtain superhydrophobic surfaces that mimick nature.
Two such models based on the works of Wenzel and Cassie-Baxter are often used to
predict CAs on rough surfaces.3 In Wenzel’s theory, the water droplet follows the surface
roughness, and a roughness parameter is introduced to account for superhydrophobic
behavior. On the other hand, the Cassie-Baxter theory assumes that the water droplet
does not penetrate inside the rough surface region but instead rests on top of the features.
Artificial superhydrophobic surfaces can be fabricated by developing a dual scale
roughness structure and tuning of surface energy.4 Methods of creating rough synthetic
110
superhydrophobic surfaces include nanoparticles, chemical etching, micro-structuring,
electrospinning, and layer-by-layer (LBL) assembly, typically involving complicated
procedures.5 Most reports on synthetic superhydrophobic surfaces involve the use of
fluorinated polymers and small molecule compounds, which are well known low-surface-
energy materials.6 A distinct disadvantage is that, fluorinated molecules are typically
more expensive and deemed to have some detrimental effects upon accumulation in the
environment.7 Therefore, the development of nonfluorinated superhydrophobic coatings
with similar properties is of value.
Figure 4.1. Structures of 2-(2,5-di(thiophen-2-yl)thiophen-3-yl)ethyl 2-bromo-2-
methylpropanoate (3T-Initiator) and terthiophene (3T).
One under-utilized technique is the use of conductive polymers. Electrochemical
methods are inexpensive, fast, and facile.8 Electrochemical deposition of substituted
organic electroactive monomers can be used to generate thin films quickly and in one
step. To date, electrodeposited conducting polymers with fluorinated functional groups
have shown to produce surfaces resistant to water and oil.6 Only a few accounts of
111
nonfluorinated conducting polymers having high water repellency have been reported.
For example, Wang et al. created superhydrophobic electroactive epoxy coatings on the
surface of steel using a nanocasting technique.9 Similarly, Pernites et al. fabricated
tunable superhydrophobic surfaces by electrodepositing a 3T derivative molecule onto
colloidally templated indium tin oxide (ITO) or gold (Au) surfaces.10
More recently
however, Wolfs and coworkers obtained surfaces ranging from hydrophilic to
superhydrophobic by simply changing the alkyl change lengths on 3,4-
ethylenedioxythiophene derivative molecules.11
Conducting polythiophenes have unique electro-optical properties. These
properties make them useful for display, semiconductor, fluorescent, and non-linear
optical materials as well as electrochromic devices.12
Electrodeposition of conducting
polymers, offers several other advantages. For example, the electroactive molecules can
be selectively deposited over large surface areas typically using cyclic voltammetry (CV)
or potentiostatic methods. Another advantage is that a variety of electrode surfaces based
on metal and semiconductor substrates such as Au, silver, aluminium, stainless steel, or
transparent substrates such as ITO can be used, emphasizing the versatility of this
method.13
Moreover, electropolymerization allows for controlled film thickness and
morphology using various parameters, e.g. scan rate and potential window.13
Herein a facile one-step method to fabricate superhydrophobic and oleophilic
surfaces is reported. Superhydrophobic surfaces were fabricated by electrodepositing a
50:50 mixture of commercially available terthiophene (3T) and 2-(2,5-di(thiophen-2-
112
yl)thiophen-3-yl)ethyl 2-bromo-2-methylpropanoate (3T-Initiator) which contains an
atom transfer radical polymerization (ATRP) initiator moiety (Figure 4.1). From these
surfaces, surface initiated ATRP (SI-ATRP) using either N-isopropylacrylamide
(NIPAM) or 3,3,4,4,5,5,6,6,7,7,8,8,9,9,10,10,10-heptadecafluorodecyl methacrylate
(HDFM) was done to enhance or tune the surface wettability.
4.2. Results and Discussion
4.2.1. Film Fabrication and Characterization
Recent research has been focused on creating template-free conducting polymer
nanostructures on electrode surfaces ranging from ITO to Au.14
One application using
template free conducting polymer nanostructures is to create superhydrophobic surfaces.
At the onset of this work our goal was to obtain superhydrophobic surfaces via
electrodeposition followed by SI-ATRP of fluorinated monomers. The ability to create a
rough surface simply by varying the electrodeposition conditions was appealing; however
the first assumption was that only upon SI-ATRP of fluorinated monomers could
superhydrophobic surfaces be achieved. In order to optimize conditions electrodeposition
of commercially available 3T onto ITO slides using CV in acetonitrile (ACN) using a
potential of 0-1.2 V, a scan rate of 10 mV/s, 0.1 M tetrabutylammonium
hexafluorophosphate (TBAH), for 20 cycles was done.
The hydrophobicity of the 3T polymer surface was evaluated using a 2 μL water
droplet for the static contact angle. Interestingly, after electrodeposition and sufficient
drying, the 3T polymeric surface had a static CAwater = 139o ± 3 (Figure 4.2a) CAdiiodo ≈
113
0o, and CAhexadec ≈ 0
o (Figure 4.2b). This nearly superhydrophobic surface was now the
spring board for future wetting manipulation. For example, I opted to incorporate the 3T-
Initiator molecule to see if similar wetting properties could be achieved. Here
electrodeposition of a mixture of 3T (5 mM) and 3T-Initiator (5 mM) was done once
again onto ITO substrates using the exact same conditions as mentioned earlier (Figure
4.3a). The electrodeposition, gave rise to a reversible and well defined redox process due
Figure 4.2. Contact angle measurements of 3T film using (a) water (b) diiodomethane
and hexadecane.
to the oxidation (anodic scans) and reduction (cathodic scans) scans. As seen in Figure
4.3a, the onset potential of the first cycle in the anodic peak is ca. 0.7 V, corresponding to
the oxidation of polymeric 3T was observed. The oxidation onset becomes lower at 0.65
V in the second cycle onward.15
This behavior is typical for polythiophenes in which the
114
higher conjugated polymer species formed resulting in a lower oxidation potential onset
for doping. The peak potential shifted to higher values as the thickness of the film
increased. The corresponding reduction peak was observed at around 0.86 V which is
attributed to the dedoping of the polythiophene.16
Figure 4.3. (a) Cyclic voltammetry diagram of the electrodeposition of 3T/3T-Initiator.
Contact angle measurements of 3T/3T-Initiator film using (b) water (c) diiodomethane
and hexadecane.
115
After electrodeposition, the CPN composite film was dried and the surface
hydrophobicity was tested using 2 and 4 μL water droplets for the static and dynamic
contact angles, respectively. Serendipitously, we found that using the 5 mM 3T and 5
mM 3T-Initiator concentration, displayed superhydrophobic properties with static water
contact angles (CAwater) of 153o ± 2 (Figure 4.3b) and low hysteresis and sliding angle
(Hw = 3 and αw = 3). Due to the low hysteresis and sliding angle, water droplets easily
Figure 4.4. XPS survey scan of 3T/3T-Initiator composite film.
rolled off of these surfaces. It should be mentioned that these values are similar to those
obtained from fluorinated films.17
Meaning, that by simply electrodepositing a
commercially available 3T mixed with the 3T-Initiator molecule, superhydrophobic
properties can be achieved. As seen in Figure 4.3c the same film was also examined for
116
static contact angle measurements in diiodomethane and hexadecane. These are
commonly used solvents to
Figure 4.5. SEM images of 3T film (with magnification of (a) ×73 (b) ×5000 (c) ×12000)
and 3T/3T-Initiator (5 mM/5 mM) composite film (with magnification of (d) ×73 (e)
×5000 (f) ×12000).
test for surface oleophobicity (oil resistance) with surface tensions of L = 50.0 mN/m
and L = 27.6 mN/m for diiodomethane and hexadecane, respectively. These surface
117
tensions are much lower than water (L = 72.8 mN/m). From these results, this
superhydrophobic film also exhibited superoleophilic character (superhydrophobic and
superoleophilic) as shown by the zero contact angle values in both organic solvents
(Figure 4.3c), a relatively rare property exhibited by the same surface. This means that
the film may be useful for the selective separation of organic solvents or oils in a water
mixture.
Figure 4.6. Static water contact angles of (a) 7.5/2.5 (b) 2.5/7.5 and (c) 0/10 mM 3T/3T-
Initiator films. SEM images of (d) 7.5/2.5 (e) 2.5/7.5 and (f) 0/10 mM 3T/3T-Initiator,
films at ×12000.
118
To further verify the adsorption of the 3T-Initiator and 3T, X-ray photoelectron
spectroscopy (XPS) was used to analyze the composite surface. As seen in Figure 4.4, the
carbon (C 1s) and sulfur peaks (S 2p and S 2s) are evident for the thiophene moieties on
both the 3T and 3T-Initiator molecules, as well as the oxygen (O 1s) and bromine (Br 3d)
elemental markers specifically unique for the 3T-Initiator. Furthermore, the survey scan
reveals that the surface is clean since the elements present are due only to the conducting
polymer film.
To further understand our systems, scanning electron microscopy (SEM) was
used. Figure 4.5 shows SEM images taken of the 3T (Figure 4.5a-c) and the 3T/3T-
Initiator composite (Figure 4.5d-f) films at magnifications of ×73 (Figure 4.5a & d),
×5000 (Figure 4.5b & e), and ×12000 (Figure 4.5c & f). SEM images showed that
electrochemical polymerization of 3T in TBAH did produce nanostructured surfaces,
resulting in the near superhydrophobic properties.
The 3T film appears to consist of spherical coral reef-like structures (Figure 4.5a-
c). In contrast, the 3T/3T-Initiator composite film (Figure 4.5d-f) exhibited both the
large scale coral reef like structure similar to the 3T film; however, the composite film
also had finer hair like structures on the periphery of the larger features. This seemingly
nature inspired approach contained both micro- and nanoscale roughness, therefore, the
superhydrophobic behavior can be correlated to the surface morphology of the film. This
is observed in previous literature, which follows the Wenzel and Cassie-Baxter models.3
119
Based on these results I opted to vary the concentrations of the 3T/3T-Initiator
(7.5 mM/2.5 mM, 2.5 mM/7.5 mM, and 0 mM/10 mM) keeping all other
electrodeposition conditions the same and test the respective CAwater (Figure 4.6a-c). As
seen in Figure 6a-c, none of these films exhibited superhydrophobic properties (CA >
150o). Once again, the investigation of the surface morphology using SEM (Figure 4.6d-
f) was performed. Here, the composite surfaces (Figure 6d and e) did exhibit a mono
scale roughness similar to that of the 3T film, however they did not show any sign of dual
scale roughness like that of the superhydrophobic 3T/3T-Initiator (5 mM/5 mM)
composite film. Similarly, without the use of 3T (Figure 4.6f), a relatively smooth film
was formed which is also apparent in the CAwater = 77o ± 5. So it appears that an
optimized condition for the electrodeposition of 3T/3T-Initiator was found, in which the
necessary surface morphology to achieve a superhydrophobic superoleophilic film
required a 1:1 ratio of 3T/3T-Initiator.
4.2.2. Surface Initiated ATRP of NIPAM
Manipulating a solid surface’s wetting characteristics and producing coatings with
either strong or poor affinity to water has found increased interest. This is especially true
since it has been found that liquid spreading can be simply controlled by changing a
surface’s roughness or surface energy. Up to now, the importances of producing films
that are able to repel water i.e. superhydrophobic have only been discussed. Another class
of surface materials growing in importance are those that can undergo complete wetting
or termed superhydrophilic (CAwater ≈ 0o).
18 Applications of superhydrophilic surfaces
120
include, anti-fogging, bio-fouling prevention and release, biomaterials, and enhanced
boiling heat transfer.20-22
Figure 4.7. (a) Conditions for SI-ATRP of NIPAM from the superhydrophobic and
superoleophilic composite film. (b) XPS survey scan after SI-ATRP of NIPAM. SEM
images after SI-ATRP of NIPAM at magnifications of (c) ×2000 and (d) ×10000.
One might suspect that zero water contact angles should be a common
occurrence; however there are only few reports. These surfaces include freshly prepared
glass substrates, or metal surfaces such as Au, copper, and silver.23,24
Other
superhydrophilic surfaces include hydroxy terminated quartz, amorphous silica, and
mica.25-27
Based on the importance of such films, herein the fabrication of
121
superhydrophilic surfaces by simply performing SI-ATRP of a well known hydrophilic
monomer i.e. NIPAM from our preexisting superhydrophobic 3T/3T-Initiator surfaces
has been demonstarted.28
Figure 4.8. (a) Side profile and (b) photographs of time dependent water adsorption into
3T/3T-Initiator composite film after SI-ATRP of NIPAM.
The fabrication of the polyNIPAM surface can be seen in Figure 4.7a. In a
typical reaction, NIPAM, methanol (MeOH), H2O, and N,N,N',N',N"-
pentamethyldiethylenetriamine (PMDETA) were placed into a Schlenk tube and
degassed with N2 for 30 min. The solution was then transferred to another Schlenk tube
containing CuBr and allowed to stir for 10 min. The mixture was then transferred to a
vial containing the superhydrophobic ITO surface. Polymerization was performed for
122
only 10 min. To further verify the formation of polyNIPAM brush, XPS was used. Proof
of the PNIPAM brush is evidenced by the increase (compared to Figure 4.2b) in signal
of the elements (N, O) in the survey scan (Figure 4.7b). The growth is even more evident
with the N 1s peak (∼400 eV).29
Similarly, SEM images also revealed interesting
changes in surface morphology. As seen in Figure 4.7c and d the once large coral reef
like structures are now blanketed with a cobweb like film i.e. the polyNIPAM. These
structures appear similar to the webs that bark lice create on trees.
Finally the static CAwater to see the affect the brush has on the once
superhydrophobic surface was tested. As seen in Figure 4.8a the water droplet at time 0 s
is 141o indicating a near superhydrophobic surface, however it was discovered that the
CAwater varied with time. After 60 s the water droplet was completely absorbed into the
electrodeposited PNIPAM composite surface (Figure 4.8b). Interestingly not only does
the droplet go to CAwater ≈ 0o, but as seen in Figure 4.8b the water droplet is adsorbed
throughout the film (goes to all four corners).
When comparing hydrophilic to superhydrophobic films, the situation is quite
different because in hydrophilic films, the solid/liquid contact is favored. Thus, the
solid/liquid interface is likely to follow the roughness of the solid, which leads to a
Wenzel state CA.30
However, a second phenomenon occurs in the hydrophilic cases.
Since the solid is rough, it can be looked upon as a kind of a porous material, were liquid
can absorb.31
This is an imbibition, since the porous material is a relatively 2-dimentional
123
feature. Consequently, a liquid/air interface develops during the imbibition known as
“hemi-wicking”, since it is intermediate between spreading and imbibition.30
4.2.3. Formation of Oleophobic Surfaces
Based on the successful SI-ATRP of NIPAM, I then turned my attention to dual
purpose surfaces i.e. both hydrophobic and oleophobic (amphiphobic). As seen earlier
our 3T/3T-Initiator film had only superhydrophobic properties. Other liquids like
diiodomethane and hexadecane quickly absorbed into the film. One method to improve
liquid repellency of a surface is to combine a suitable chemical structure (low surface
energy) with a topographical microstructure (roughness). Previous research includes
preparing fractal surfaces, plasma treating polymer surfaces, functionalizing roughened
substrates with perfluoroalkyl groups, preparing gel-like roughened polymers through
solvent processing, phase separating polymer blends, densely packing aligned carbon
nanotubes, self-assembling monolayers on copper films, and sol-gel approach.32-39
In order to change the wetting properties of our superhydrophobic,
superoleophilic coating, we performed SI-ATRP of HDFM. SI-ATRP was performed in
DMF using CuBr and PMDETA as the ligand at room temperature for only 1 hr. After
SIP the films were carefully dried, CA of various solvents were recorded. As seen in
Figure 4.9a-c, the wetting properties changed dramatically when compared to the 3T/3T-
Initiator composite film. Although the CAwater = 155o
± 2 only changed slightly, the
liquids with much lower surface tensions i.e. diiodomethane (Figure 4.9b) and
hexadecane (Figure 4.9c) did show near superoleophobic CAs. This was a complete
124
reversal from the non fluorinated surface as seen earlier. In addition to hexadecane and
diiodomethane, CAs of decalin (Figure 4.9d, L = 31.5 mN/m), nitrobenzene (Figure
4.9e, L = 43.9 mN/m), and cooking oil (Figure 4.9f, L = 31 mN/m) were also examined.
As evident from the images the film is quite impervious to a variety of different liquids.
Figure 4.9. Contact angles of (a) water, (b) diiodomethane, (c) hexadecane, (d) decalin,
(e) nitrobenzene, (f) and cooking oil on 3T/3T-Initiator composite film after SI-ATRP of
HDFM.
125
4.3. Conclusions
In conclusion, a novel one-step approach to fabricate superhydrophobic and
superoleophilic coating by using CV was reported. Additional SI-ATRP of NIPAM or
HDFM further resulted in interesting superhydrophilic and oleophobic surfaces
respectively. Future works are in progress to test whether the coating/s can also be used
for corrosion prevention, bacterial/protein resistance, and for a host of stimuli responsive
properties with temperature and pH.
4.4. Experimental
4.4.1. Materials
Reagent chemicals TBAH (99 %), CuBr (99 %), triethylamine (99 %), HDFM
(97 %), bromine (99%), NIPAM (99%), PMDETA (99 %), 2-(tributylstannyl) thiophene
(97%), nitrobenzene (99 %), decalin (99 %), diiodomethane (99%), HDFM (99%), and
hexadecane (99 %) were purchased from Aldrich and were used without further
purification unless otherwise indicated. Chemicals trans-dichlorobistriphenylphosphine)
palladium, ethyl thiophene-3-acetate (98%), and 3T (99 %) were purchased from Alfa
Aesar and were used without further purification. 2-bromoisobutyryl bromide (99 %) was
purchased from Tokyo Chemical Industry and also used without any purification.
Deionized water, methanol (MeOH), dimethylformamide (DMF), isopropanol, hexanes,
toluene, acetonitrile (ACN), and tetrahydrofuran (THF) were used in the formation of
ITO slides, synthesis, and polymerization reactions. HDFM monomers containing
inhibitor were passed through a column with alternating layers of activated neutral
126
alumina and inhibitor remover replacement packing to remove the inhibitor and were
stored at -20 °C. NIPAM was recrystallized using hexane and stored at -20 °C.
4.4.2. Surface Preparation
ITO substrates were first cut into 2.5 × 0.7 cm slides. The slides were then
cleaned using an Alconix solution followed by sonicating in isopropanol, followed by
hexanes, and toluene for 10 min each. The slides were then dried using N2 gas followed
by plasma cleaning for 3 min. The slides were either used immediately or stored in a
desiccator.
4.4.3. Electrodeposition
The electropolymerization of the 3T or 3T/3T-Initiator was done using cyclic
voltammetry with an Autolab PGSTAT 12 potentiostat (Metro Ohm) in a standard three-
electrode measuring cell (a fabricated electrochemical cell with a diameter of 1.0 and
volume of 0.785 cm3, made of Teflon) with platinum wire as the counter electrode,
Ag/AgCl wire as the reference electrode and the ITO substrate as the working electrode.
All electrodepositions were performed using CV in acetonitrile (ACN) using a potential
of 0-1.2 V, a scan rate of 10 mV/s, 0.1 M TBAH, for 20 cycles. After electrodeposition,
the resulting film was washed with ACN thrice. The electropolymerized substrate was
dried with nitrogen gas and stored in a desiccator for at least 12 hr before performing
wettability studies
127
4.4.4. Surface Initiated ATRP
In a typical reaction SI-ATRP of HFDM was performed as such. First 1.06 g of
HFDM (2 mmol) was added in 10 mL of DMF and mixed using a magnetic bar under N2
gas for 30 min. Then CuBr (28 mg, 0.2 mmol) and PMDETA (52 mg, 0.3 mmol) were
added to the solution and mixed, resulting in a homogeneous green solution. After 10 min
of stirring the solution was transferred to a 3rd Schlenk tube containing the coated ITO
substrate. Polymerization was performed for 1 hr. Afterwards the slide was removed and
carefully washed using DMF followed by H2O and MeOH. The slide was dried with N2
and further dried in a vacuum desiccator before performing CA measurements. SI-ATRP
of NIPAM was performed by first mixing 1 g of NIPAM, 5.0 X 10-2
ml of PMDETA in 5
ml of H2O and 5 ml of MeOH. The solution was degassed for 30 min. Afterwards, the
solution was transferred to a 2nd flask containing 12.7 mg of CuBr and allowed to stir for
10 min. The solution was then transferred to a third flask containing the coated ITO
substrate and allowed to polymerize for 10 min.
4.4.5. Synthesis of 3T-Initiator
The synthesis of 3T-OH was done according to previous literature (Scheme
4.1).40
The synthesis of 3T-Initiator was performed by first dissolving 1 g of 3T-OH (3.4
X 10-3
mols) and 415 mg (4.1 X 10-3
mols) in 20 ml of DCM. The reaction flask was
sealed and degassed for 10 min. After degassing 562 mg (4.1 X 10-3
mols) of isobutyl
bromide was added dropwise via a syringe. The reaction was allowed to continue
overnight. Purification was done by washing 3X with water dried with sodium sulfate,
128
filtered, and then subjected to column chromatography using 1/4 hexane/DCM (68 %
yield). 1H NMR (δ ppm in CDCl3): 7.34-7.00 (m, 7H), 4.40 (t, 2H, J = 6.87 Hz), 3.14 (t,
2H, J = 6.87 Hz), 1.95 (s, 6H). 13C NMR (δ ppm in CDCl3): 171.77, 165.81, 136.94,
135.15, 134.71, 131.33, 128.01, 127.79, 126.61, 126.56, 125.98, 124.72, 123.87, 65.59,
55.81, 30.85, 28.27.
Scheme 4.1. Synthesis of 3T-Initiator
4.4.6. Characterization
Nuclear magnetic resonance (NMR) spectra were recorded on a General Electric
QE-500 spectrometer operating at 500 MHz for 1H NMR. X-ray Photoelectron
Spectroscopy (XPS) was done using a PHI 5700. X-ray photoelectron spectrometer was
equipped with a monochromatic Al KR X-ray source (hν = 1486.7 eV) incident at 90o,
129
relative to the axis of a hemispherical energy analyzer. The spectrometer was operated
both at high and low resolutions with pass energies of 23.5 and 187.85 eV, respectively, a
photoelectron take off angle of 45o from the surface, and an analyzer spot diameter of 1.1
mm. All spectra were collected at room temperature with a base pressure of 1 X 10-8
Torr. The peaks were analyzed first by background subtraction, using the Shirley routine.
All the samples were completely dried in argon gas prior to XPS measurements. Cyclic
voltammetry was performed in a conventional three-electrode cell, using an Autolab
PGSTAT 12 potentiostat (Brinkmann Instruments (now MetroOhm USA)). The
potentiostat was controlled using GPES software (version 4.9). Static water contact angle
(WCA) measurements were accomplished using a CAM 200 optical contact angle meter
(KSV Instruments Ltd). Note that the WCA value was acquired only when the water
droplet was dropped at a relatively far distance (0.3 cm) away from the surface since no
reading can be measured if the droplet comes into contact with the substrate. For dynamic
contact angle measurements, the angles were measured using a Ramé-Hart model 100
contact angle goniometer. The liquids were dispensed and withdrawn using a Matrix
Technologies micro Electrapette 25. Contact angles were collected and averaged from
measurements on four distinct slides using three separate drops per slide. SEM analysis
was done in field emission scanning electron microscopy (FE-SEM) using a JSM 6330F
JEOL instrument operating at 15 kV.
4.5. References
1. Barthlott, W.; Neinhuis C.; Planta 1997, 202, 1 8.
130
2. (a) Pernites, R. B.; Santos, C. M.; Maldonado, M.; Ponnapati, R. R.; Rodrigues, D.
F.; Advincula, R. C. Chem. Mater. Article, ASAP. (b) Yuan, S. J.; Xu, F. J.;
Pehkonen, S. O.; Ting, Y. P.; Neoh, K. G.; Kang, E. T. Biotechnol. Bioeng. 2009,
103, 268. (c) Barthlott, W. Nat. Mater. 2003, 2, 301. (d) Foster, E. L.; De Leon, A.
C. C.; Mangadlao, J.; Advincula, R. J. Mater. Chem. 2012, 22, 11025.
3. (a) Wenzel, R. N. Ind. Eng. Chem. 1936, 28, 988. (b) Cassie, A. B. D.; Baxter, S.
Trans. Faraday Soc. 1944, 40, 546–551. (c) Baxter, S.; Cassie, A. B. D. J. Text.
Inst. 1945, 36, T67.
4. Feng, L.; Li, S. H.; Li, Y. S.; Li, H. J.; Zhang, L. J.; Zhai, J.; Song, Y. L.; Liu, B.
Q.; Jiang, L.; Zhu, D. B. Adv Mater. 2002, 14, 1857.
5. (a) Sun. T. L.; Feng, L.; Gao, X. F. Jiang, L. Acc. Chem. Res. 2005, 38, 644. (b)
Puretsky, N.; Ionov, L. Langmuir 2011, 27, 3006. (c) Xiong, D.; Liu, G.; Hong, L.
Chem. Mater. 2011, 23, 4357. (d) Shiu, J. Y.; Kuo, C. W.; Chen, P.; Mou, C. Y.
Chem. Mater. 2004, 16, 561.
6. (a) Houde, M.; Martin, J. W.; Letcher, R. J.; Solomon, K. R.; Muir, D. C. G.
Environ. Sci. Technol. 2006 , 40, 3463. (b) Giesy, J. P.; Kannan, K. Environ. Sci.
Technol. 2001, 35, 1339.
7. (a) Chiba, K.; Kurogi, K.; Monde, K.; Hashimoto, M.; Yoshida, M.; Mayama, H.;
Tsuji, K. Colloids Surf. A 2010, 354, 234.(b) Darmanin, T.; Guittard, F. J. Am.
Chem. Soc. 2009, 131, 7928. (c) Darmanin, T.; Guittard, F. J. Mater. Chem. 2009,
19, 7130.
131
8. (a) Xie, Q.; Xu, J.; Feng, L.; Jiang, L.; Tang, W.; Luo, X.; Han, C. C. Adv. Mater.
2004, 16, 302. (b) Yan, H.; Kurogi, K.; Mayama, H.; Tsujii, K. Angew. Chem., Int.
Ed. 2005, 44, 3453. (c) Kurogi, K.; Yan, H.; Mayama, H.; Tsujii, K. J. Colloid
Interface Sci. 2007, 312, 156.
9. Weng, C. J.; Chang, C. H.; Chen, S. W.; Yeh, J. M.; Hsu, C. L.; Wei, Y. Chem.
Mater. 2011, 23, 2075.
10. Pernites, R. B.; Ponnapati, R. R.; Advincula, R. C. Adv. Mater. 2011, 23, 3207.
11. Wolfs, M.; Darmanin, T.; Guittard, F. Macromolecules, ASAP article.
12. Roncali, J. Chem. Rev. 1992, 92, 711.
13. Lange, U.; Roznyatouskaya, N. V.; Mirsky, V. M. Anal. Chim. Acta 2008, 614, 1.
14. Wan, M. Adv. Mater. 2008, 20, 2926.
15. Schrebler, S.; Grez, P.; Cury, P.; Veas, C.; Merino, M.; Gòmez, H.; Còrdova, R.;
del Valle, M. J. Electroanal. Chem. 1997, 430, 77.
16. Berlin, A. In Electrical and Optical Polymer Systems - Fundamentals, Methods, and
Applications; Marcel Dekker: New York, 1993; p 47.
17. (a) Darmanin, T.; Guittard, F. J. Colloid Interface Sci. 2009, 335, 146. (b)
Darmanin, T.; Guittard, F.; Amigoni, S.; Taffin de Givenchy, E.; Noblin, X.;
Kofman, R.; Celestini, F. Soft Matter 2011, 7, 1053. (c) Darmanin, T.; Taffinde
Givenchy, E.; Amigoni, S.; Guittard, F. Langmuir 2010, 26, 17596.
18. Drelich, J.; Chibowski, E.; Meng, D. D.; Terpilowaki, K. Soft Matter 2011, 7, 9804.
132
19. (a) Yang, X. G.; Zhang, F. Y.; Lubawy, A. L.; Wang, C. Y. Electrochem. Solid-
State Lett. 2004, 7, 408. (b) Maharbiz, M. M.; Holtz, W. J.; Howe, R. T.; Keasling,
J. D. Biotechnol. Bioeng. 2004, 85, 376.
20. Baier, R. J. Mater. Sci.: Mater. Med. 2006, 17, 1057.
21. Hasuda, H.; Kwon, O. H.; Kang, I. K.; Ito, Y. Biomaterials 2005, 26, 2401.
22. (a) Li, C.; Wang, Z.; Wang, P. I.; Peles, Y.; Koratkar, N.; Peterson, G. P. Small
2008, 4, 1084. (b) Chen, R.; Lu, M.-C.; Srinivasan, V.; Wang, Z.; Cho, H. H.;
Majumdar, A. Nano Lett. 2009, 9, 548.
23. Quere, D. Rep. Prog. Phys. 2005, 68, 2495.
24. (a) Smith, T. J. Colloid Interface Sci. 1980, 75, 51. (b) Schrader, M. E. J. Phys.
Chem. 1974, 78, 87.
25. Lamb, R. N.; Furlong, D. N. J. Chem. Soc., Faraday Trans. 1982, 78, 61.
26. Asay, D. B.; Barnette, A. L.; Kim, S. H. J. Phys. Chem. C 2009, 113, 2128.
27. Yaminsky, V.; Ninham, B.; Karaman, M. Langmuir 1997, 13, 5979.
28. Kim, D. J.; Kang, S. M.; Kong, B.; Kim, W.-J.; Paik, H.-J.; Choi, H.; Choi, I. S.
Macromol. Chem. Phys. 2005, 206, 1941.
29. (a) Fujie, T.; Park, J. Y.; Murata, A.; Estillore, N. C.; Tria, M. C. R.; Takeoka, S.;
Advincula, R. C. ACS Appl. Mater. Interfaces 2009, 1, 1404. (b) Estillore, N. C.;
Park, J. Y.; Advincula, R. C. Macromolecules 2010 , 43, 6588.
30. Bico, J.; Thiele, U.; Quéré, D. Colloid Surface A 2002, 206, 41.
31. J. Bico, C. Tordeux, D. Quére, Europhys. Lett. 55 (2001) 214.
32. Onda, T.; Shibuichi, S.; Satoh, N.; Tsujii, K. Langmuir 1996, 12, 2125.
133
33. (a) Morra, M.; Occhiello, E.; Garbassi, F. Langmuir 1989, 5, 872. (b) Woodward,
I.; Schofield, W. C. E.; Roucoules, V.; Badyal, J. P. S. Langmuir 2003, 19, 3432.
34. Tsujii, K.; Yamamoto, T.; Onda, T.; Shibuichi, S. Angew. Chem. Int. Ed. 1997, 9,
36, 1011.
35. Erbil, H. Y.; Demirel, A. L.; Avci, Y.; Mert, O. Science 2003, 299, 1377.
36. Xie, Q.; Xu, J.; Feng, L.; Jiang, L.; Tang, W.; Luo, X.; Han, C. C. Adv Mater. 2004,
16, 302.
37. (a) Lau, K. K. S.; Bico, J.; Teo, K. B. K.; Chhowalla, M.; Amaratunga, G. A. J.;
Milne,W. I.; McKinley, G. H.; Gleason, K. K. Nano Lett. 2003, 3, 1701. (b) Feng,
L.; Li, S.; Li, Y.; Li, H.; Zhang, L.; Zhai, J.; Song, Y.; Liu, B.; Jiang, L.; Zhu, D.
Adv. Mater. 2002, 14, 1857. (c) Li, H.; Wang, X.; Song, Y.; Liu, Y.; Li, Q.; Jiang,
L.; Zhu, D. Angew. Chem. Int. Ed. 2001, 40, 1743.
38. Wang, S.; Feng, L.; Liu, H.; Sun, T.; Zhang, X.; Jiang, L.; Zhu, D. Chem. Phys.
Chem. 2005, 6, 1475.
39. Sheen, Y. -C.; Huang, Y. -C.; Liao, C.-S.; Chou, H. -Y.; Chang, F. -C. J. Polym.
Sci., Part B: Polym. Phys. 2008, 46, 1984.
40. R. Ponnapati, M. J. Felipe, J. Y. Park, J. Vargas, and R. Advincula,
Macromolecules, 2010, 43, 10414.
134
Chapter 5: Tunable and Polymerizable Multifunctional Electroactive
Coatings
5.1. Introduction
Recently, industry and biomedical researchers have focused on preparing
synthetic surfaces capable of repelling water or have a water contact angle (CAwater)
greater then 150o, i.e. superhydrophobic surfaces. This interest is attributed to their
potential properties and applications in self-cleaning systems, biocorrosion inhibition,
antifouling marine coatings, microfluidics, and anti-ice adhesion systems.1 The
inspiration for many of the synthetically designed superhydrophobic films comes from
nature. For example, plants such as the lotus and the Lady Mantle have leaves that exhibit
very poor wetting.2 Many varieties of insects also posses superhydrophobic properties
such as the butterfly and water strider. A typical attribute to this non-wetting behavior in
both plants and insects is the hierarchical and periodic roughness contained on their
respective surfaces. This naturally occurring phenomenon has now become a spring
board for synthetic design strategies and surface control. For example, Ma et al. reported
common strategies and materials used for surface structuring to mimic natural design.3 It
should be mentioned however that, most of these methods include lengthy lithographic
steps or require sophisticated instrumental setup, limiting their practical application.
135
Although somewhat understudied, electrochemical polymerization of
electroactive monomers can be an alternative route to fabricate superhydrophobic
surfaces.4 To date, most studies involving electrochemistry to fabricate superhydrophobic
coatings, require the incorporation of fluorinated substituents attached to the electroactive
monomers. Research has shown however, that accumulation of fluorinated compounds in
the environment can be detrimental, necessitating the search for alternative routes.
Despite the numerous efforts demonstrating superhydrophobic surfaces, there are few
studies investigating their biomaterial applications.5 For example, Genzer et al. reported
current developments in superhydrophobic coatings and their applications for mediating
bio-adhesion and functionality.6
Figure 5.1. (a) Structure of 2-(2,5-di(thiophen-2-yl)thiophen-3-yl)ethyl 2-bromo-2-
methylpropanoate (3T-Initiator). (b) Static water contact angle of 1:1 3T/3T-Initiator
coated ITO. (c) Diagram of electrodeposition conditions on ITO or steel substrates.
136
Tunable adsorption or resistance of protein or bacteria to surfaces can have
various environmental, medical, and industrial applications. For example, both biosensors
and immunoassays require the adsorption or selective adhesion of proteins to surfaces.7
Typically, controlled adhesion of proteins to a surface, require materials such as
macromolecules, which are either physically or chemically adsorbed to a surface.8 One
application being the formation of biofilms for controllable growth of bacterial cells.9
One approach to prevent biofouling is to make the surface superhydrophobic.10-13
For
example, Marmur et al. claimed that biofouling can be reduced by minimizing the surface
area of the film to water.14
Since bacteria generally require water to multiply, using a
superhydrophobic coating, reduces the capacity of bacteria to achieve bacterial
adhesion.15
Another important function of coatings is corrosion control. Corrosion control is
an important field of interest to any economy since its mitigation is built into
manufacturing and the fabrication of engineered steel structures. One of the current
industrial practices for anticorrosion is to treat the surface of metals with chromium-
containing compounds. However, there are concerns regarding the adverse health and
environmental effects of chromium compounds. In the past decade, it has been reported
that polyaniline (PANI) coatings have better anticorrosion properties on metallic
substrates than several polymers.16
More recently Weng et al. reported a method for
fabricating anticorrosive superhydrophobic coatings prepared by mimicking a
Xanthosoma Sagittifolium-leaf-like electroactive epoxy.17
Here they used a combined
137
approach of micro-contact printing (CP) and thermal curing of an electroactive epoxy
coating.
Here, a facile one step method to fabricate superhydrophobic surfaces that serve
both as tunable coatings for bacterial adhesion and demonstrate anticorrosion properties
is reported. The superhydrophobic surfaces were fabricated by electrodepositing a 1:1
mixture of commercially available terthiophene (3T) and 2-(2,5-di(thiophen-2-
yl)thiophen-3-yl)ethyl 2-bromo-2-methylpropanoate (3T-Initiator) which contains an
atom transfer radical polymerization (ATRP) moiety (Figure 5.1a). From these surfaces,
surface initiated ATRP (SI-ATRP) using 3,3,4,4,5,5,6,6,7,7,8,8,9,9,10,10,10-
heptadecafluorodecyl methacrylate (HDFM) was also done to enhance the surface
wettability and corrosion properties.
5.2. Results and discussions
5.2.1. Film Formation
Recently our group has fabricated polymerizable superhydrophobic (Figure 5.1b)
coatings using a novel one-step approach.1f
As seen in Figure 5.1c, electrodeposition was
done on an indium tin oxide (ITO) substrate using CV. The anti-wetting surface with
CAwater = 153o ± 2 (Figure 5.1b) was fabricated using a novel one-step approach via
electrodeposition of an acetonitrile (ACN) solution containing 3T (5 mM), 3T-Initiator (5
mM), and tetrabutylammonium hexafluorophosphate (TBAH, 0.1M).1f
This method
allowed direct grafting of the conducting polymers, where the superhydrophobic property
arise from the surface morphology of the electro-grafted material. For example, scanning
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electron microscopy (SEM) images taken at magnifications of ×73 (Figure 5.2a), ×2000
(Figure 5.2b), and ×12000 (Figure 5.2c) show irregular spherical coral reef-like
structures as well as finer hair-like structures on the periphery of the larger features
(Figure 5.2c). Similarly, stylus profilometry measurements also showed that the film’s
roughness parameter was Rq = 21.23 m (Figure 5.2d). It has been shown that micro-
and nano-structuring can serve as a barrier, ultimately resisting the adhesion of water to a
surface.18
Figure 5.2. SEM images of 3T/3T-Initiator composite film on ITO substrate at taken at
magnifications of (a) ×73, (b) ×2000, and (c) ×12000. (d) Line profile of stylus
profilometry measurements.
139
Dynamic CAwater measurements were also used to verify the static CAwater. The
3T/3T-Initiator composite surface displayed high advancing (θadv = 152o ± 1) and
receding (θrec = 149o ± 1) water contact angles. Contact angle hysteresis is then obtained
by taking the difference between the advancing and receding contact angles.19
Contact
angle hysteresis can be used to predict whether the surface will demonstrate a sliding
water droplet.20
Since our superhydrophobic surface has a very low hysteresis of <5o, we
believed that a water droplet should freely roll off the surface.
5.2.2. Superhydrophobic Composites with Different Functional Groups
Complementary to ATRP, reversible-addition fragmentation chain transfer
(RAFT) polymerization is based on a chain transfer agent.21a
A distinct advantage of
RAFT polymerization is its relative simplicity and versatility. RAFT polymerization has
also been successfully used to prepare polymer brushes via SIP. Another polymerization
technique that can be used to create polymer brushes is via surface-initiated ring-opening
metathesis polymerization (SI-ROMP), which utilizes late transition metal catalysts.21b
As a living/controlled polymerization technique, SI-ROMP offers the capability of
preparing uniform polymer brushes and block copolymers by metathesis methods.
Similarly, click chemistry has also gained notoriety in functionalizing surfaces. The most
widely used click reaction is the copper-catalyzed azide alkyne cycloaddition (CuAAC)
reaction.21c
The CuAAC reaction is one representative of a family of efficient chemical
reactions, which are modular, widely applicable, relatively insensitive to solvents, and pH
ranges, while resulting in high yields.21c
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Based on the above techniques, efforts were focused to investigate if other
functional groups, i.e. RAFT agents (Figure 5.3a), terminal alkynes (Figure 5.3b), and
norbornene (Figure 5.3c) moieties could be electrodeposited using the identical
Figure 5.3. Structures of (a) 2-(2,5-di(thiophen-2-yl)thiophen-3-yl)ethyl 4-
(benzodithioyl)-4-cyanopentanoate (3T-CTA), (b) prop-2-ynyl 2-(2,5-di(thiophen-2-
yl)thiophen-3-yl)acetate (3T-Alkyne), (c) and (bicyclo[2.2.1]hept-5-en-2-yl)methyl 2-
(2,5-di(thiophen-2-yl)thiophen-3-yl)acetate (3T-Nb) molecules. Static water contact
angle of (d) 1:1 3T/3T-CTA, (e) 1:1 3T/3T-Alkyne, (f) and 1:1 3T/3T-Nb coated ITO.
SEM images (magnification ×12000) of (g) 3T/3T-CTA, (h) 3T/3T-Alkyne, (i) and
3T/3T-Nb superhydrophobic composite films.
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conditions as in the 3T-Initiator case, in order to create superhydrophobic surfaces. As
seen in Figure 5.3d-f, all the composite films had CAwater > 150o. These results show that
as long as the electro-grafting conditions are held constant, superhydrophobic surfaces
can be fabricated independently of the orthogonal functional group on the 3T derivative.
SEM images (magnification ×12000, Figure 5.3g-i) show similar dual scale roughness as
the 3T/3T-Initiator superhydrophobic composite film.
5.2.3. Tunable Wetting Behavior
Another interesting property of electro-grafted materials is the ability to
reversibly dope and dedope the coating.22
For example, Manukyan et al. reported
reversible wetting from a Cassie-Baxter state to the Wenzel state by using an electrical
potential on a superhydrophobic surface.23
These dual property coatings, have
applications ranging from stimuli-responsive devices such as intelligent microfluidic
switches, sensors, transparent semiconductor coatings, and electrochromic devices.24
In order to investigate the redox properties of the conducting 3T/3T-Initiator
composite film, a constant oxidation potential of 1.05 V was applied using a typical
monomer free condition using the same three electrode system mentioned earlier. Since
electrodeposition was done on a transparent conducting ITO substrate, the change in the
redox properties of the composite film, could be monitored using UV-vis. Immediately
after electrodeposition, the UV-Vis spectrum shows a maximum absorption peak (λmax) at
460 nm. This peak is known as the π to π* transition of the polythiophene film (Figure
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Figure 5.4. (a) UV-Vis spectra of 3T/3T-Initiator composite film before and after
applying a potential of 1.05 V. (b) Static water contact angles of undoped and doped
3T/3T-Initiator composite film.
143
5.4a).25
At this point the conducting 3T/3T-Initiator composite film is considered neutral
or undoped.
Next, the absorption spectra after applying a potential of 1.05 V to the 3T/3T-
Initiator composite film i.e. doping was obtained. During the application of the oxidation
potential, conducting polymers are known to become positively charged. The oxidized
film accepts negatively charged counterions from the TBAH supporting electrolyte in the
solution in order to maintain neutrality. As seen in Figure 5.4a the UV-vis spectrum
shows a new broad peak between 600 to 800 nm. This peak is attributed to the formation
of polarons in the conjugated polythiophene polymer and their complex redox ion
coupling with the hexafluorophosphate ions.26
Upon doping, the once superhydrophobic film was now found to have a CAwater ≈
76° ±4 (Figure 5.4b). The large change in CAwater (CAwater = 77o) can be attributed
mainly to changes in the film’s surface morphology.27
For example, when comparing the
SEM images of the undoped surface (Figure 5.2a-c) to the SEM images of the now
doped surface (1.05 V), taken at magnifications of ×73 (Figure 5.5a), ×2000 (Figure
5.5b), and ×12000 (Figure 5.5c) one can see a relatively clear smoothening of the
surface. Although Fig. 6b and c do seem to have overall smoother morphologies when
compared to their undoped (Figure 5.2b and c) counterparts, the most distinct
morphology change seems to be the SEM images taken at magnifications ×73 Figure
5.2a and Figure 5.5a. In the case of the undoped surface (0 V), the rougher surface is
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able to trap a greater volume of air, contributing to the Cassie–Baxter models. In the case
of the doped surface (1.05 V), the smoothening can be attributed to the polythiophene
collapse and the counter ions occupying the pores. Interestingly, dedoping the conducting
polymer, by applying a constant potential of 0 V, reverted to its original rough and
porous morphology (Figure 5.5d). This may be due to the removal of the counter ions.
Hence the film returns to its superhydrophobic state with a water contact angle > 150°.
Figure 5.5. SEM images of doped 3T/3T-Initiator composite film on ITO substrate taken
at magnifications of (a) ×73, (b) ×2000, and (c) ×12000. (d) Reversible static water
contact angles of the 3T/3T-Initiator composite film via potential switching between 1.05
V (doping) and 0 V (dedoping).
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The ability of the surfaces to inhibit bacterial attachment was tested by incubating
the films with the model bacteria B. subtillis. Figure 5.6a-c depicts fluorescent images of
the B. subtillis adsorbed onto the undoped (Figure 5.6a), doped (Figure 5.6b) polymeric
surfaces, and bare ITO (Figure 5.6c) after staining with SYTO 9 dye. Significant
reduction of bacterial adhesion was observed for the undoped surface (p < 0.05) when
compared to bare ITO and the doped film. These results are consistent with previous
literature. For
Figure 5.6. Bacterial adhesion results after incubation for 2 h with B. subtillis solution on
different surfaces (1 mm2 x 1 mm
2): Fluorescence images of (a) dedoped, (b) doped, and
(c) bare ITO 3T/3T-Initiator composite film. (d) Bar graph of the statistical analysis of
the bacterial cell adhesion on the three surfaces. Notes: (1) * denotes results statistically
significant difference compared to the unmodified control (p < 0.05, ANOVA on ranks).
146
(2) ** denotes results statistically significant difference compared to the doped surface (p
< 0.05, ANOVA on ranks).
example, Liu and coworkers showed that bacterial adhesion was significantly reduced on
a superhydrophobic surface.28
Similarly, Pernites et al. also found that by doping a
polyterthiophene derivative on an ITO substrate resulted in enhanced adhesion of E
coli.29
The reduced adhesion to the undoped surface can be attributed to the minimized
contact between the aqueous solution containing the bacteria and the superhydrophobic
surface.14
It should be mentioned however, that electrostatic interaction between the net
positively charged polymeric surface and the negatively charged B. subtilis may also play
an important factor contributing to the increase in bacterial attachment on the doped
surface. In the case of the doped and bare ITO, the adhesion of more bacteria is possibly
due to the hydrophilic nature of both surfaces. The lower CAwater allows for better contact
between the aqueous media and the surface.
5.2.4. Steel Optimization and SI-ATRP
Another advantage of using electrodeposition is that the electroactive molecules
can be deposited onto any conducting or electrode substrate. One of the most important
conductive substrates used in industry is steel; however, steel is susceptible to corrosion.
Based on our success of creating superhydrophobic ITO, we now turned our attention to
fabricating superhydrophobic steel slides.
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Figure 5.7. CV diagram of the electrodeposition of a 5 mM 3T and 5 mM 3T-Initiator
solution onto a steel slide.
Here similar conditions as the superhydrophobic ITO i.e. using ACN as solvent
with a potential of 0-1.2 V, a scan rate of 10 mV/s, 5 mM 3T, 5 mM 3T-Initiator, and 0.1
M TBAH were used, however we found that only 10 cycles we required for steel slides.
The CV diagram is depicted in Figure 5.7. The electrodeposition, gave rise to a
reversible redox process due to the oxidation (anodic scans) and reduction (cathodic
scans) scans. As seen in Figure 5.7, the onset potential of the first cycle in the anodic
peak is ca. 0.7 V, corresponding to the oxidation of polymeric terthiophene was
observed. The oxidation onset becomes lower at 0.65 V in the second cycle onward.30
This behavior is typical for polythiophenes in which the higher conjugated polymer
species formed resulted in a lower oxidation potential onset for doping. The peak
potential shifted to higher values as the thickness of the film increased. The
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corresponding reduction peak was observed at around 0.86 V which is attributed to the
dedoping of the polythiophene.31
Figure 5.8. Static water and diiodomethane contact angles on the 3T/3T-Initiator
composite film on a steel slide.
After electrodeposition, the composite film was dried and the surface
hydrophobicity was tested. Once again, using the 5 mM 3T and 5 mM 3T-Initiator
concentration, also displayed superhydrophobic properties (CAwater = 153o ± 2) the same
as the ITO substrate (Figure 5.8). As seen in Figure 5.8a the same slide was also used to
examine the static contact angle measurement of diiodomethane (CAdiiodo).
Diiodomethane is a common solvent used to test for surface oleophobicity (oil resistance)
with a surface tension (L = 50.0 mN/m) much lower than water (L = 72.8 mN/m).
Interestingly, the superhydrophobic steel coating also exhibited superoleophilic character
CAdiiodo ≈ 0o. It should be mentioned that having both superhydrophobic and
superoleophilic properties are rare characteristic exhibited by the same surface. This
means that the film may be useful for the selective separation of organic solvents or oils
in a water mixture.
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Figure 5.9. SEM images of 3T/3T-Initiator composite film-coated on steel slide.
Up to now, the 3T/3T-Initiator composite film had only superhydrophobic
properties. Diiodomethane was quickly absorbed into the film. One method to improve
liquid repellency of a surface is to combine a suitable chemical structure (low surface
energy) with a topographical microstructure (roughness). Previous research includes
preparing fractal surfaces, plasma treating polymer surfaces, functionalizing roughened
substrates with perfluoroalkyl groups, preparing gel-like roughened polymers through
solvent processing, phase separating polymer blends, densely packing aligned carbon
nanotubes, self-assembling monolayers on copper films, and sol-gel approach.32-39
Atom transfer radical polymerization (ATRP) is a controlled/living radical
polymerization technique. It allows for the formation of carbon-carbon bond through a
transition metal catalyst. The atom transfer step, usually a halogen, is the key step in the
reaction responsible for uniform polymer chain growth. Here in order to change the
wetting properties of our superhydrophobic, superoleophilic coating we performed SI-
ATRP of HDFM. SI-ATRP was done in DMF using CuBr and N,N,N',N',N"-
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pentamethyldiethylenetriamine (PMDETA) as the ligand for 1 hr. After SIP the films
were carefully dried and CA of water, diiodomethane, and hexadecane (CAhexadec) were
found.
Figure 5.10. (a) Digital photo images of the movement of a water droplet on the
superhydrophobic 3T/3T-Initiator composite steel surface at sliding angle ≈ 0o. Digital
photo images of (b) static diiodomethane and hexadecane contact angles and (c) the
movement of a diiodomethane droplet on the superoleophobic 3T/3T-Initiator composite
steel surface at sliding angle 3o ± 1.
Upon SI-ATRP of HDFM, it was found that the CAwater = 156o ± 3. Although this
is only a slight change, it should be mentioned that even at very low tilting angles the
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water droplet freely moved on the now fluorinated surface. The CAwater = 156o ± 3 could
only be measured in some instances when the water droplet came to a rest on the coating
(note: in no case did the droplet remain in the same spot it was initially released). In most
instances, even when the steel coated slide was at a tilt angle ~ 0o, the water droplet
simply rolled off the surface (Figure 5.10a). This made it difficult to get accurate CAwater
of the entire surface. The data however, do reveal the extremely high repellency of the
coating towards wetting.
Liquids with much lower surface tensions i.e. diiodomethane and hexadecane
(Figure 5.10b) did show superoleophobic CAs. This means that our once superoleophilic
coating had a complete reversal making it now a superamphiphobic coating after SI-
ATRP. Even more interesting was the fact that a droplet of diiodomethane would freely
roll off of the steel-coated slide even at low tilting angles of 3o ± 1 (Figure 5.10c).
5.2.5. Corrosion Studies
The ability for a coating to provide corrosion protection depends on three factors:
(1) water sorption of the coating, (2) transport of water into the coating, and (3)
accessibility of water to the coating/ substrate interface. Therefore, it is reasonable to
believe that the 3T/3T-Initiator composite film with its high water repellency should be
able to effectively prevent the water adsorbing into the coating and saturating the steel
substrate. Although the static and dynamic CAwater was tested, an investigation to see how
the coating behaved when immersed in water was also performed. As seen in Figure
5.11a, when the steel-coated slide was immersed into water, one could see the bending of
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the water contact line at the air/water interface. This is indicative of surfaces that have
poor wetting characteristics, meaning that the water’s cohesive forces are greater than the
water’s attraction to the coated steel slide. The repulsion ultimately, forming a convex
curvature on or around the steel coating. Similarly, as seen from the side view (Figure
5.11b), the immersed slide also exhibits a distinct air/water interface deeply penetrating
into the water. This passive air layer should prevent the sorption and diffusion of water to
the steel coating. SI-ATRP of the HDFM to see if there would be any difference in the
corrosion properties in the two coating was also performed.
Figure 5.11. Digital photo images of 3T/3T-Initiator composite coated steel immersed in
water taken from the (a) front and (b) the side.
Based on the poor wetting results, it seemed reasonable that the coating would
exhibit a superior corrosion resistance in a wet environment. Our superhydrophobic
3T/3T-Initiator composite coating on the steel (SH-steel) electrode was immersed into a
corrosive medium i.e. 3.5 M aqueous NaCl electrolyte at pH 7. Corrosion current
information can be obtained by the Tafel extrapolation method. Here the large cathodic
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and anodic polarizations provide the respective curves for the corrosion processes.40
Extrapolation of these curves to their point of intersection provides both the corrosion
potential and the corrosion current. Corrosion protection studies were performed on
samples immersed for 7 days. Tafel-plot measurements for the three sample
configurations in corrosive medium are shown in Figure 5.12a.
Tafel plots of the bare steel electrode measured at an operational temperature of
25 oC gave a corrosion potential of Ecorr = 0.15 mV and a corrosion current (Icorr) of 5.89
X 10-8
A/cm2. Moreover, the Icorr of the SH-steel electrode was ca. 1.29 X 10
-10 μA/cm
2,
which was significantly lower than that of bare steel. These results indicated that
corrosion protection of SH-steel substrates results from the formation of an impermeable
layer between the aqueous media and the metal surface. Similarly, in the case of the
fluorinated 3T/3T-Initiator composite film (FSH-steel) a dramatic decrease in the Icorr
(Icorr = 3.51 X 10-12
μA/cm2) when compared to bare steel was observed.
The protection efficiency of the coating were evaluated using eq 1:41
where Icorr(C) and Icorr are the corrosion current values with and without the coating. Using
this equation it was found that the protection efficiency of the SH-steel after 7 days was
99.80 %. Similarly, the FSH-steel displayed protection efficiency after 7 days of 99.99 %.
Although the FSH-steel did display higher protection efficiencies, the near perfect values
in both cases, shows that our 3T/3T-Initiator composite films can be used for corrosion
154
prevention even without the need for fluorinated functionality. To further understand the
high performance of SH-steel and FSH-steel, electrochemical impedance spectroscopy
was employed. Impedance spectroscopy is a non-destructive method of determining
several system parameters. These parameters include the degree of coating degradation,
coating capacitance, and resistance. These are related to the extent of water and ion
absorption.42
The electrochemical behavior and film degradation were monitored by applying
alternating current of 10 mV and by varying frequency from 10 kHz to 1 mHz.43
To
avoid perturbation of the sample, the frequency is usually swept from higher frequency to
lower frequency.44
The Bode plots obtained for SH-steel, FHS-steel, and bare steel are
shown in Figure 5.12b. The Bode magnitude plot for bare steel shows an overall
impedance value of 50.1 kΩ cm2 at the low frequency end. Here, the low impedance
value could be due to high capacitance and/or very low resistance of the bare steel.44
Large values of the capacitance has been related to the high extent at which water has
been in contact with the steel.45
Also, small resistance values have been related to the
formation of ionically conducting path across the substrate brought about by diffusion of
electrolytes.46
The SH-steel and FSH-steel on the other hand showed overall impedance
values of 7.94 X 104 kΩ cm
2 and 79.4 X 10
4 kΩ cm
2, respectively. These higher values
when compared to the bare steel further validate the Tafel plot data.
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Figure 5.12. (a) Tafel and (b) Bode plots of bare steel, SH-steel, and FSH-steel after
being immersed in 0.5 M aqueous NaCl electrolyte at pH 7 solution for 7 days.
5.3. Conclusions
Tunable bacterial adhesion and self-cleaning properties were demonstrated on a
conducting superhydrophobic surface. By simply manipulating the redox property of the
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conducting coating, the wettability of the surface was easily changed, which drastically
changed the adhesion of B. subtillis. The current system therefore, can be useful for
fabricating smart coatings onto a variety of conducting surfaces, in order to tune the
resistance or adhesion of bacteria. Similarly, due to the incorporation of an ATRP moiety
within the superhydrophobic coating, SI-ATRP of HDFM was performed on a steel slide.
Subsequent static water, diiodomethane, and hexadecane contact angles revealed that the
steel coated surface was now superamphiphobic.
Similarly, this work also demonstrated that the superhydrophobic steel coating
could have possible applications for corrosion prevention even without the need of either
fluorinated molecules or other toxic inorganic materials. Currently future work in
underway to examine how the current coating performs under a variety of different
conditions i.e. low pH’s and various temperatures.
5.4. Experimental
5.4.1 Materials
Reagent chemicals TBAH (99 %), CuBr (99 %), triethylamine (TEA, 99 %),
HDFM (97 %), bromine (99 %), PMDETA (99 %), dicyclohexylcarbodiimide (DCC,
99%), 4-dimethylaminopyridine (DMAP, 99%), 2-(tributylstannyl) thiophene (97 %),
nitrobenzene (99 %), decalin (99 %), diiodomethane (99 %), and hexadecane (99 %)
were purchased from Aldrich and were used without further purification unless otherwise
indicated. Chemicals trans-dichlorobistriphenylphosphine) palladium, ethyl thiophene-3-
acetate (98 %), and terthiophene (99 %) were purchased from Alfa Aesar and were used
157
without further purification. 2-bromoisobutyryl bromide (99 %) was purchased from
Tokyo Chemical Industry and also used without any purification. Deionized water,
methanol (MeOH), dimethylformamide (DMF), isopropanol, hexanes, toluene, ACN, and
tetrahydrofuran (THF) were used in the formation of ITO slides, synthesis, and
polymerization reactions. HDFM monomers containing inhibitor were passed through a
column with alternating layers of activated neutral alumina and inhibitor remover
replacement packing to remove the inhibitor and were stored at -20 °C.
5.4.2 Surface Preparation
ITO substrates were first cut into 2.5 × 0.7 cm slides. The slides were then
cleaned using an Alconix solution followed by sonicating in isopropanol, followed by
hexanes, and toluene for 10 min each. The slides were then dried using N2 gas followed
by plasma cleaning for 3 min. The slides were either used immediately or stored in a
desiccator.
5.4.3 Electrodeposition
The electropolymerization of the 3T or 3T/3T-Initiator was done using cyclic
voltammetry using an Autolab PGSTAT 12 potentiostat (Metro Ohm) in a standard three-
electrode measuring cell (a fabricated electrochemical cell with a diameter of 1.0 and
volume of 0.785 cm3, made of Teflon) with platinum wire as the counter electrode,
Ag/AgCl wire as the reference electrode and the ITO substrate as the working electrode.
All electrodepositions were performed using CV in ACN using a potential of 0-1.2 V, a
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scan rate of 10 mV/s, 0.1 M TBAH, for either 20 or 10 cycles. After the
electrodeposition, the resulting film was washed with ACN thrice.
5.4.4 Surface-initiated ATRP
In a typical reaction SI-ATRP of HDFM was performed as such. First 1.06 g of
HFDM (2 mmol) was added in 10 mL of DMF and mixed using a magnetic bar under N2
gas for 30 min. Then CuBr (28 mg, 0.2 mmol) and PMDETA (52 mg, 0.3 mmol) were
added to the solution and mixed, resulting in a homogeneous green solution. After 10 min
of stirring the solution was transferred to a 3rd Schlenk tube containing the coated ITO
substrate. Polymerization was performed for 1 hr. Afterwards the slide was removed and
carefully washed using DMF followed by H2O and MeOH. The slide was dried with N2
and further dried in a vacuum desiccator before performing CA measurements.
5.4.5. Synthesis of 3T-CTA
The synthesis of 3T-CTA was done according to previous litereature.47
5.4.6. Synthesis of 3T-Alkyne
Scheme 5.1. Synthesis of 3T-Alkyne
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The synthesis of 3T-COOH was done according to previous literature.48
The
synthesis of 3T-Alkyne (Scheme 5.1) was performed by first combining 3T-COOH (1.0
g, 3.3 mmol), propargyl alcohol (190 mg, 3.4 mmol), and DMAP (21 mg, 0.17 mmol).
The mixture was dissolved in 50 ml of DCM, bubbled with nitrogen, and placed in an ice
bath. After which, a solution of DCC (700 mg, 3.4 mmol) in DCM was added dropwise
to the reaction mixture. This was then stirred vigorously for 30 mins, warmed to room
temperature and stirred overnight. The solid by-product was filtered off and the filtrate
was washed with water and brine solution. The mixture was then subjected to column
chromatography using 1/4 hexanes/DCM (72% yield). 1H NMR (δ ppm in CDCl3): 7.34-
7.00 (m, 7H), 4.55 (t, 2H, J = 4.8 Hz), 3.89 (t, 2H, J = 4.8 Hz), 2.49, (t,1H, J = 2.3 Hz).
5.4.7 Synthesis of 3T-Nb
The synthesis of 3T-Nb was done according to previous litereature.49
5.4.8 Bacterial Adhesion Measurements
A single isolated Bacillius subtilis K12 MG1655 (B. subtillis) colony was
inoculated in 5 mL Tryptic Soy Broth (TSB) (Oxoid, England) overnight at 35 oC and
200 rpm. The bacterial culture was then centrifuged at 3000 rpm for 10 min, and the
bacteria pellet was resuspended in phosphate buffer solution (PBS, 0.01M, pH = 7.4)
(Fisher Scientific, USA). The optical density of the suspension was adjusted to 0.5 at 600
nm, which corresponds to a concentration of 107 colony forming units per milliliters
(CFU/mL). The doped and undoped colloidal-polymeric films and unmodified ITO
substrate were individually placed in a 12 well-plate (Falcon). To each well was added
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2.0 mL of bacterial culture, and then incubated at 37 oC (without shaking) for 2 h. The
samples were then removed and briefly washed with PBS buffer. The bacterial cells
attached to the surface were stained with 3 μL of SYTO 9 dye solution for 10 min from
Molecular Probes (Leiden, The Netherlands),. The surfaces were placed in microscope
slides, covered with a coverslip, and imaged using BX 51 Olympus Fluorescent
Microscope (OLYMPUS, Japan) equipped with a DP72 digital camera under 100X
objective. All images were acquired and analyzed using Image-Pro Plus software
(MediaCybernetics, USA).
5.4.9. Statistical Analysis
The amount of attached bacterial cells was expressed as the mean number of
bacteria per image field acquired for at least 7 pictures per replicate sample (where 3
replicates were prepared per sample) conducted on a minimum of two separate
experiments while the error bars are expressed as its standard deviation. Statistical
differences between median values were done using pairwise comparison by ANOVA on
ranks test using Sigma Plot Software (version 11). Significance was accepted at a level of
p < 0.05.
5.4.10. Characterization
Nuclear magnetic resonance (NMR) spectra were recorded on a General Electric
QE-500 spectrometer operating at 500 MHz for 1H NMR. X-ray Photoelectron
Spectroscopy (XPS) was done using a PHI 5700. X-ray photoelectron spectrometer was
equipped with a monochromatic Al KR X-ray source (hν = 1486.7 eV) incident at 90o,
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relative to the axis of a hemispherical energy analyzer. The spectrometer was operated
both at high and low resolutions with pass energies of 23.5 and 187.85 eV, respectively, a
photoelectron take off angle of 45o from the surface, and an analyzer spot diameter of 1.1
mm. All spectra were collected at room temperature with a base pressure of 1 X 10-8
Torr. The peaks were analyzed first by background subtraction, using the Shirley routine.
All the samples were completely dried in argon gas prior to XPS measurements. Cyclic
voltammetry was performed in a conventional three-electrode cell, using an Autolab
PGSTAT 12 potentiostat (Brinkmann Instruments (now MetroOhm USA)). The
potentiostat was controlled using GPES software (version 4.9). Static water contact angle
(WCA) measurements were accomplished using a CAM 200 optical contact angle meter
(KSV Instruments Ltd). Note that the CAwater value was acquired only when the water
droplet was dropped at a relatively far distance (0.3 cm) away from the surface since no
reading can be measured if the droplet comes into contact with the substrate. For dynamic
contact angle measurements, the angles were measured using a Ramé-Hart model 100
contact angle goniometer. The liquids were dispensed and withdrawn using a Matrix
Technologies micro Electrapette 25. Contact angles were collected and averaged from
measurements on four distinct slides using three separate drops per slide. SEM analysis
was done in field emission scanning electron microscopy (FE-SEM) using a JSM 6330F
JEOL instrument operating at 4 or 5 kV.
162
5.5 References
1. (a) Yuan, S. J.; Xu, F. J.; Pehkonen, S. O.; Ting, Y. P.; Neoh, K. G.; Kang, E. T.
Biotechnol. Bioeng. 2009, 103, 268. (b) Barthlott, W. Nat. Mater. 2003, 2, 301. (c)
Feng, X. J.; Jiang, L. Adv. Mater. 2006, 18, 3063 3078. (d) Blossey, R. Nat. Mater.
2003, 2, 301. (e) Shiu, J.-Y.; Chen, P. Adv. Funct. Mater. 2007, 17, 2680. (f) Foster,
E. L.; De Leon, A. C. C.; Mangadlao, J.; Advincula, R. J. Mater. Chem. 2012, 22,
11025.
2. Barthlott, W.; Neinhuis, C. Planta 1997, 202, 1.
3. Ma, M.; Hill, M. Curr. Opin. Colloid Interface Sci. 2006, 11, 193.
4. Darmanin, T.; Guittard, F. J. Am. Chem. Soc. 2009, 131, 7928.
5. (a) Shiu, J.-Y.; Kuo, C.-W.; Whang, W.-T.; Chen, P. Lab Chip 2010, 10, 556. (b)
Koc, Y.; de Mello, A. J.; McHale, G.; Newton, M. I.; Roach, P.; Shirtcliffe, N. J.
Lab Chip 2008, 8, 582.
6. Genzer, J.; Efimenko, K. Biofouling 2006, 22, 339.
7. Benmakroha, Y.; Zhang, S.; Rolfe, P. Med. Biol. Eng. Comput. 1995, 33, 811.
8. (a) Kumar, N.; Parajuli, O.; Hahm, J.-I. J. Phys. Chem. B 2007, 111, 4581. (b)
Kumar, N.; Hahm, J.-I. Langmuir 2005, 21, 6652. (c) Liu, D.; Wang, T.; Keddie, J.
L. Langmuir 2009, 25, 4526.
9. (a) Park, J. Y.; Yoo, Y. J. Appl. Microbiol. Biotechnol. 2009, 82, 415. (b) Dash, R.
R.; Gaur, A.; Balomajumder, C. J. Hazard. Mater. 2009, 163, 1. (c) Yakimov, M.
M.; Timmis, K. N.; Golyshin, P. N. Curr. Opin. Biotechnol. 2007, 18, 257. (d)
Gavrilescu, M.; Pavel, L. V.; Cretescu, I. J. Hazard. Mater. 2009, 163, 475. (e)
163
Vinther, F. P.; Brinch, U. C.; Elsgaard, L.; Fredslund, L.; Iversen, B. V.; Torp, S.;
Jacobsen, C. S. J. Environ. Qual. 2008, 37, 1710. (f) Castillo Mdel, P.; Torstensson,
L.; Stenstrom, J. J. Agric. Food Chem. 2008, 56, 6206. (g) Close, M.; Dann, R.;
Ball, A.; Pirie, R.; Savill, M.; Smith, Z. J. Water Health 2008, 6, 83. (h) Dopson,
M.; Halinen, A. K.; Rahunen, N.; Bostrom, D.; Sundkvist, J. E.; Riekkola-
Vanhanen, M.; Kaksonen, A. H.; Puhakka, J. A. Biotechnol. Bioeng. 2008, 99, 811.
10. (a) Shen, M.; Wagner, M. S.; Castner, D. G.; Ratner, B. D.; Horbett, T. A.
Langmuir 2003, 19, 1692. (b) Mrksich, M.; Sigal, G. B.; Whitesides, G. M.
Langmuir 1995, 11, 4383. (c) Goodman, S. L.; Simmons, S. R.; Cooper, S. L.;
Albrecht, R. M. J. Colloid Interface Sci. 1990, 139, 561. (d) Sigal, G. B.; Mrksich,
M.; Whitesides, G. M. J. Am. Chem. Soc. 1998, 120, 3464. (e) Baier, R. E.; Meyer,
A. E.; Natiella, J. R.; Natiella, R. R.; Carter, J. M. J. Biomed. Mater. Res. 1984, 18,
337.
11. (a) Chapman, R. G.; Ostuni, E.; Liang, M. N.; Meluleni, G.; Kim, E.; Yan, L.; Pier,
G.; Warren, H. S.; Whitesides, G. M. Langmuir 2001, 17, 1225. (b) Sadana, A.
Chem. Rev. 1992, 92, 1799.
12. (a) Banerjee, I.; Pangule, R. C.; Kane, R. S. Adv. Mater. 2011, 23, 690. (b) Pompe,
T.; Zschoche, S.; Herold, N.; Salchert, K.; Gouzy, M.-F.; Sperling, C.; Werner, C.
Biomacromolecules 2003, 4, 1072. (c) Johnell, M.; Larsson, R.; Siegbahn, A.
Biomaterials 2005, 26, 1731. (d) Klement, P.; Du, Y. J.; Berry, L.; Andrew, M.;
Chan, A. K. C. Biomaterials 2002, 23, 527. (e) Ferrer, M. C. C.; Yang, S.;
Eckmann, D. M.; Composto, R. J. Langmuir 2010, 26, 14126. (f) Liu, M.; Yue, X.;
164
Dai, Z.; Ma, Y.; Xing, L.; Zha, Z.; Liu, S.; Li, Y. ACS Appl. Mater. Interfaces 2009,
1, 113. (g) Benhabbour, S. R.; Liu, L.; Sheardown, H.; Adronov, A.
Macromolecules 2008, 41, 2567. (h) Prime, K. L.; Whiteside, G. M. J. Am. Chem.
Soc. 1993, 115, 10714. (i) Gombotz, W. R.; Guanghui, W.; Horbett, T. A.;
Hoffman, A. S. J. Biomed. Mater. Res. 1991, 25, 1547. (j) Jeon, S. I.; Andrade, J.
D.; de Gennes, P. G. J. Colloid Interface Sci. 1991, 142, 159. (k) Grunze, M.;
Harder, P.; Spencer, N. D.; Hahner, G.; Feldman, K. J. Am. Chem. Soc. 1999, 121,
10134. (l) Prime, K. L.; Whitesides, G. M. Science 1991, 252, 1164.
13. (a) Bers, A. V.; Wahl, M. Biofouling 2004, 20, 43. (b) Hoipkemeier-Wilson, L.;
Schumacher, J. F.; Carmen, M. L.; Gibson, A. L.; Feinberg, A. W.; Callow, M. E.;
Finlay, J. A.; Callow, J. A.; Brenan, A. B. Biofouling 2004, 20, 53. (c) Zhang, H.;
Lamb, R.; Lewis, J. Sci. Technol. Adv. Mater. 2006, 6, 236.
14. Marmur, A. Biofouling 2006, 22, 107.
15. Lichter, J. A.; Van Vliet, K. J.; Rubner, M. F. Macromolecules 2009, 42, 8573.
16. (a) McAndrew, T. P.; Miller, S. A.; Gilicinski, A. G.; Robeson, L. M. Polym.
Mater. Sci. Eng. 1996, 74, 204. (b) Wessling, B.; Posdorfer, J. Electrochim. Acta
1999, 44, 2139. (c) Kinlen, P. J.; Silverman, D. C.; Jeffreys, C. R. Synth. Met. 1997,
85, 1327. (d) Camalet, J. L.; Lacroix, J. C.; Aeiyach, S.; Chaneching, K.; Lacaze, P.
C. Synth. Met. 1998, 93, 133. (e) DeBerry, D. W. J. Electrochem. Soc. 1985, 132,
1022.
17. Weng, C.-J.; Chang, C. –H.; Peng, C. –W.; Chen, S.-W.; Yeh, J. –M. Chem. Mater.
2011, 23, 2075.
165
18. Puretskiy, N.; Ionov, L. Langmuir 2011, 27, 3006.
19. Miwa, M.; Nakajima, A.; Fujishima, A.; Hashimoto, K.; Watanabe, T. Langmuir
2000, 16, 5754.
20. Steele, A.; Bayer, I.; Loth, E. Nano Lett. 2009, 9, 501.
21. (a) Chiefari, J.; Chong, Y. K.; Ercole, F.; Krstina, J.; Jeffery, J.; Le, T. P. T.;
Mayadunne, R. T. A.; Meijs, G. F.; Moad, C. L.; Moad, G; Rizzardo, E.; Thang, S.
H. Macromolecules 1998, 31, 5559. (b) Buchmeiser, M. R. Chem. Rev. 2000, 100,
1565. (c) Binder, W. H.; Sachsenhofer, R. Macromol. Rapid Commun. 2008, 29,
952.
22. Lahann, J.; Mitragotri, S.; Tran, T. -N.; Kaido, H.; Sundaram, J.; Choi, I. S.; Hoffer,
S.; Somorjai, G. A.; Langer, R. A. Science 2003, 299, 371.
23. Manukyan, G.; Van Den Ende, J. M. Oh , D.; Lammertink, R. G. H.; Mugele, F.
Phys. Rev. Lett. 2011 , 106 , 014501-1.
24. (a) Feng, X. J.; Feng, L.; Jin, M. H.; Zhai, J.; Jiang, L.; Zhu, D. B. J. Am. Chem.
Soc. 2004 , 126 , 62. (b) Wang, S. T.; Feng, L.; Liu, H.; Sun, L. T.; Zhang, X.;
Jiang, L.; Zhu, D. B. ChemPhysChem. 2005 , 6 , 1475. (c) Sun, T. L.; Wang, G. J.;
Feng, L.; Liu, B. Q.; Ma, Y. M.; Jiang, L.; Zhu, D. B. Angew. Chem. Int. Ed. 2004 ,
43 , 357.
25. Xia, C.; Park, M.-K.; Advincula, R. C. Langmuir 2001, 17, 7893.
26. Ikeda, T.; Higuchi, M.; Kurth, D. G. J. Am. Chem. Soc. 2009, 131, 9158.
27. Fu, Q.; Rao, G. V. R.; Basame, S. B.; Keller, D. J.; Artyushkova, K.; Fulghum, J.
E.; Lopez, G. P. J. Am. Chem. Soc. 2004 , 126 , 8904.
166
28. Liu, T.; Dong, L.; Liu, T.; Yin, Y. Electrochim. Acta 2010, 55, 5281.
29. Pernites, R. B.; Santos, C. M.; Maldonado, M.; Ponnapati, R. R.; Rodrigues, D. F.;
Advincula, C. R. Chem. Mater 2012, 24, 870.
30. Schrebler, S.; Grez, P.; Cury, P.; Veas, C.; Merino, M.; Gòmez, H.; Còrdova, R.;
del Valle, M. J. Electroanal. Chem. 1997, 430, 77.
31. Berlin, A. In Electrical and Optical Polymer Systems - Fundamentals, Methods, and
Applications; Marcel Dekker: New York, 1993; p 47
32. Onda, T.; Shibuichi, S.; Satoh, N.; Tsujii, K. Langmuir 1996, 12, 2125.
33. (a) Morra, M.; Occhiello, E.; Garbassi, F. Langmuir 1989, 5, 872. (b) Woodward,
I.; Schofield, W. C. E.; Roucoules, V.; Badyal, J. P. S. Langmuir 2003, 19, 3432.
34. Tsujii, K.; Yamamoto, T.; Onda, T.; Shibuichi, S. Angew. Chem. Int. Ed. 1997, 36,
1011.
35. Erbil, H. Y.; Demirel, A. L.; Avci, Y.; Mert, O. Science 2003, 299, 1377.
36. Xie, Q.; Xu, J.; Feng, L.; Jiang, L.; Tang, W.; Luo, X.; Han, C. C. Adv Mater. 2004,
16, 302.
37. (a) Lau, K. K. S.; Bico, J.; Teo, K. B. K.; Chhowalla, M.; Amaratunga, G. A. J.;
Milne, W. I.; McKinley, G. H.; Gleason, K. K. Nano Lett. 2003, 3, 1701. (b) Feng,
L.; Li, S.; Li, Y.; Li, H.; Zhang, L.; Zhai, J.; Song, Y.; Liu, B.; Jiang, L.; Zhu, D.
Adv. Mater. 2002, 14, 1857. (c) Li, H.; Wang, X.; Song, Y.; Liu, Y.; Li, Q.; Jiang,
L.; Zhu, D. Angew. Chem. Int. Ed. 2001, 40, 1743.
38. Wang, S.; Feng, L.; Liu, H.; Sun, T.; Zhang, X.; Jiang, L.; Zhu, D. Chem. Phys.
Chem. 2005, 6, 1475.
167
39. Y. –C. Sheen, Y. –C. Huang, C. –S. Liao, H. –Y. Chou, F. –C. Chang, J. Polym.
Sci., Part B: Polym. Phys. 2008, 46, 1984.
40. Mitra, A.; Wang, Z. B.; Cao, T. G.; Wang, H. T.; Huang, L. M.; Yan, Y. S. J.
Electrochem. Soc. 2002, 149, B472. (b) Beving, D. E.; McDonnell, A. M. P.; Yang,
W. S.; Yan, Y. S. J. Electrochem. Soc. 2006, 153, B325. (c) Cheng, X. L.; Wang, Z.
B.; Yan, Y. S. Electrochem. Solid-State Lett. 2001, 4, B23.
41. Kamaraj, K.; Karpakam, V.; Sathiyanarayanan, S.; Venkatachari, G. Mater. Chem.
Phys. 2010, 122, 123.
42. Thierry, D.; Amirudin, A. Progress in Organic Coatings 1995, 26, 1.
43. Ates, M. Progress in Organic Coatings 2011, 71, 1.
44. (a) Kannan, M. B.; Gomes, D.; Dietzel, W.; Abetz, V. Surface and Coatings
Technology 2008, 202, 4598. (b) Hamdy, A; El-Shenawy, El-Bitar, T. Int. J.
Electrochem. Sci. 2006, 1, 171.
45. Reinhard, G.; Rammelt, U. Progress in Organic Coatings 1992, 21, 205.
46. Mansfeld, F. J. Appl. Electrochem. 1995, 25, 187.
47. Grande, C. D.; Tria, M. C.; Jiang, G.; Ponnapati, R.; Advincula, R. Macromolecules
2011, 44, 966.
48. Ponnapati, R.; Felipe, M. J.; Park, J. Y.; Vargas, J.; Advincula, R. Macromolecules
2010, 43, 10414.
49. Kumar, A.; Jang, S.-Y.; Padilla, J.; Otero, T. F.; Sotzing, G. A. Polymer 2008, 49,
3686.
168
Chapter 6. Nanopatterning of Terthiophene Pendent Polymer Brushes
6.1. Introduction
Nanolithography techniques are useful for the design of new artificial structures,
and the simulation of important morphological behaviors of inorganic, metal, or
polymeric materials including semiconductor surfaces. They also allow for the
investigation of physical and chemical properties of novel nanopatterned materials. The
optimization of these properties, permits the use of nanopatterned materials for data
storage, optoelectronics, and molecular electronics devices.1
To date, surface probe microscopy (SPM) nanolithography techniques are
typically used for the formation of site specific nanoscale structures.2 These techniques
include dip-pen nanolithography (DPN) and thermo-mechanical indentation which
usually do not change the chemical composition of the matrix materials.3 This is
accomplished by the removal or deposition of materials on the sample’s surface. -DPN
uses an atomic force microscope (AFM) tip as a tool to deposit molecules through
capillary forces on top of a solid substrate.4 Similarly, thermo-mechanical indentation
uses a heated AFM tip to produce patterns in a thermoplastic film. Another method to
fabricate surface features using chemical reactions is anodic oxidation. Anodic oxidation
controls electron flow by creating insulating gate oxides on conducting metal substrates.5
Finally, electrostatic nanolithography is another class of lithography in which a primary
mechanism for structure generation is mass transport, arising from joule heating effects.6
169
This arises as a consequence of locally applied tip/sample bias voltages. Electrochemical
nanolithography is of focus towards the fabrication of controlled oxide patterns, making
electrochemical nanolithography applicable for semiconductor patterning.7 Controlled
oxidation by SPM can result in a height change of oxide patterns on a semiconductor
surface with applied voltage and tip velocity.8
Figure 6.1. Illustration of (a) polymer brush film fabrication (b) and nanopatterning using
current sensing AFM.
Recently, insulating polymeric materials have been patterned and the material’s
physical and chemical properties studied using Joule heating generated from conducting
nanolithographic techniques.9 For example, Lyuksyutov et al. reported on an electrostatic
170
nanolithography technique based on these principles.10
Here, the film rested on a
grounded conductive layer, while they were able to generate patterns by biasing a highly
conductive tungsten carbide AFM tip across the polymer film. When compared to more
conventional patterning techniques, these methods eliminate the need for some
intermediate steps such as chemical etching and the use of sacrificial layers. This also
allowed in situ measurements and analysis of material response with the different
variables involved in the experiment.
Typically, nanopatterning of electroactive polymer materials has been by direct
electrochemical DPN (E-DPN) using electroactive monomers as ink, facilitating the
localized transport of the monomer from the AFM tip to the substrate.11
The formation of
nanowires was observed via a direct-writing process after an electrochemical reaction
with the AFM tip. This first suggested that E-DPN can be useful for the development of
novel conducting polymer patterns. More recently, electroactive precursor polymer films
have been fabricated using spincoating, Langmuir-Blodgett (LB) techniques, and layer-
by-layer (LBL).12
These films served as precursors towards the fabrication of conjugated
polymer nanopatterns. This also allowed for control over the spatial and electrical
properties of the resulting nanostructures based on bias voltage and writing speed.
However, spincoating, LB techniques, and LBL suffer drawbacks in terms of stability on
the surface.13
Chemisorption is a technique often used to address the stability issues
however, this requires multiple processing steps.14
171
Another way to functionalize surfaces is to perform surface initiated
polymerization (SIP). SIP has a major advantage over other methodologies, in that SIP
allows for the direct tethering of polymers onto surfaces.15
This is ideal for surfaces
coatings, because of the high grafting densities this affords. Surface-initiated
polymerization using controlled living radical polymerization techniques such as
reversible-addition fragmentation chain transfer (RAFT), atom transfer radical
polymerization (ATRP), and nitroxide mediated polymerization (NMP) permit the
synthesis of tethered polymers with various functionalities and exhibit control over
molecular weight (MW), i.e. polydispersity, composition, and macromolecular
architectures.15
Of the controlled living radical polymerization techniques mentioned
above, RAFT polymerization possesses a unique advantage due to its relative simplicity
and functional group tolerance.16
Another advantage of RAFT polymerization is that
conventional free radical polymerizations can be readily converted into a RAFT process
by adding an appropriate RAFT agent, such as a dithioester, dithiocarbamate, or
trithiocarbonate compound, while other parameters i.e. monomer, initiator, solvent, and
temperature, can be kept constant.17
Herein the fabrication of precisely controlled nanopatterns on precursor polymer
(polyterthiophene) brushes (Figure 6.1a) using the ECNL technique (Figure 6.1b) is
reported. Unlike direct nanowriting on an insulating solid-state film in electrolyte
solution, the patterning feature can be facially done by applying a bias voltage between a
conductive AFM tip and the polymer film at ambient conditions. The resulting localized
patterns can be characterized by investigating the surface morphological features (AFM
172
topographic change) and electrical properties of the conductive pattern (current
mapping). These patterns rely on various parameters such as applied bias voltage and
scan rate. To our knowledge this is the first report of an electroactive polymer brush
being patterned in this manner.
6.2. Results and Discussion
6.2.1. Substrate Modification
Electropolymerization of the macroinitiator was performed in a three-electrode
cell, with an acetonitrile (ACN) solution containing 3T-CTA (0.5 mM) and 0.1 M
tetrabutylammonium hexafluorophosphate (TBAH). This was done using cyclic
voltammetry (CV) at a scan rate of 50 mV/s and by sweeping the potential from 0 to 1.2
V versus the Ag/AgCl reference electrode and platinum (Pt) counter electrode on gold
(Au) or indium tin oxide (ITO) substrates. The CV diagram is depicted in Figure 6.2.
The CV diagram of the electro-grafting process shows a reversible redox process due to
the oxidation (anodic scans) and reduction (cathodic scans) scans. As seen in Figure 6.2,
the onset potential of the first cycle in the anodic peak is ca. 0.70 V. This anodic peak is
due to the oxidation of polymeric terthiophene. The oxidation onset becomes lower (0.45
V) in the second cycle onward.18
This behavior is typical for most electrodeposition
procedures involving CV. Here the higher conjugated polymer species formed resulted in
a lower oxidation potential onset for doping. The corresponding reduction peak was
observed at around 0.63 V due to the dedoping of the polythiophene.19
The substrates
were then rinsed with ACN, tetrahydrofuran (THF), ACN and dried under vacuum.
173
Figure 6.2. Cyclic voltamogram of electrodeposition of 3T-CTA.
The successful surface modification with the conjugate polymer network of 3T-
CTA was confirmed by ellipsometry, fourier transform infrared spectroscopy (FT-IR).
The electrodeposited film at 10 cycles gave an average thickness of 6.23 ± 0.78 nm. The
FT-IR spectra (Figure 6.3a) reveals the distinct peaks of both the conjugated polymer
network (CPN) composed of terthiophene repeating units and the RAFT CTA moiety.
For example, a strong characteristic out of plane broad vibrational peak at 839 cm-1
arising from (C-H) ring of the thiophene rings is clearly seen.20
Similarly, the peak c.a.
1735 cm-1
is attributed the carbonyl functional group on the CTA moiety of the CPN of
the 3T-CTA.20
174
Figure 6.3. (a) FT-IR spectra of electrodeposited 3T-CTA. (b) UV-vis spectra of
electrodeposited 3T-CTA and grafted 3T-Methacrylate. AFM topography images of (c)
electrodeposited 3T-CTA (d) and grafted 3T-Methacrylate.
Surface-initiated polymerization (SIP) of 3T-Methacrylate was performed by first
placing 1.0 g of 3T-Methacrylate and 0.77 g of AIBN in 8 mL of dry toluene. Three
freeze pump thaw cycles were performed on the solution mixture. Afterwards, the
solution was then transferred via syringe to an already degassed Schlenk tube containing
either the 3T-CTA gold or ITO coated substrate. The polymerization was then allowed to
proceed for 48 hr.
175
After polymerization the brush thickness was found to be 24.8 ± 2.2 nm using
ellipsometry. Similarly, UV-Vis spectroscopy was also employed to monitor the progress
of the surface modification (Figure 6.3b). The absorption spectra is characterized by a
broad peak at 465 nm, attributed to the π to π* transition of the polythiophene peak. This
confirms the presence of the CPN from the electrodeposited CPN of 3T-CTA.21
After SI-
RAFT polymerization of 3T-Methacrylate a new peak was observed at 355 nm,
indicating the successful growth of the PVK brush. Atomic force microscopy (AFM)
analysis also supported the surface modification as shown by the differences in
topography after each step (Figure 6.3c and d). Bigger globular domains were formed
after the formation of the 3T-Methacrylate brush (Figure 6.3d) as compared to the
electrodeposited 3T-CTA (Figure 6.3c).
6.2.2. Patterning
One application for thin semiconducting polymer films is memory devices and
information storage.12
In order to create such devices, new methodologies are being
studied so that robust and controllable methods can be created. Herein, current sensing
atomic force microscopy (CS-AFM) to investigate the nanopatterning on the precursor
3T-Methacrylate brush films and examine the effects on the patterns by varying the
applied bias and writing speed was utilized. Patterns were achieved due to the application
of the applied voltage bias from the AFM tip resulting in the formation of cross-linked
polythiophene species. This occurs because, anodic oxidation generates radical cations
176
through the electroactive sites contained on the thiophene moieties (Figure 6.4a),
providing the mechanism for electropolymerization (Figure 4b).12
Figure 6.4. (a) Structure of 3T-CTA and demonstration of reactive sites. (b) Mechanism
of electropolymerization of 3T-CTA.
The data obtained from the localized electropolymerization of polymer brush
based on the oxidation of the electroactive terthiophene pendent molecules can be seen in
Figure 6.5a-d. Figure 6.5a-d show the AFM topograpaphic images (Figure 6.5a and b)
and subsequent plotted AFM line profiles heights (Figure 6.5c and d) of the films by
varying either the writing speed (Figure 6.5a and c) or the applied bias (Figure 6.5b and
d). As seen in Figure 6.5a four individual lines are evident after applying a constant
voltage bias (-10 V) at different writing speeds ranging from 0.4, 0.6, 0.8 to 1.0 μm/s
177
(from left to right) performed under ambient conditions. The relative heights of the line
patterns were determined using AFM profilometry with the corresponding lines and was
found to be 2.9 ±0.1, 2.1, 1.9, and 1.7 nm (Figure 6.5c), corresponding to the writing
speeds of 0.4, 0.6, 0.8 to 1.0 μm/s, respectively. From these results, it suggests that under
a constant voltage bias the height of the line patterns decreased with increasing writing
speed in a near linear manner. Consequently, the contact time between the conductive tip
and the specific location of the precursor polymer film exhibited good control over
pattern height. In other words, with fixed applied bias, at lower writing speeds, higher
nanopatterns can be expected. The previous investigation showed a similar relationship
between the pattern height and tip contact time, in which either spin-coated PVK or LBL
fabricated films were used to form nanopatterns under a constant bias.12b,12c
The dependence of pattern height as a function of voltage bias is shown in Figure
5b. Interestingly, after applying a constant writing speed of 0.4 μm/s at different voltage
bias ranging from -10,- 8,- 6 to -4 V (from left to right) only three individual lines are
evident corresponding to the locations of the -10, -8, to -6 V bias (Figure 5b). In the case
of the -4 V area, no pattern was evident. Once again a near linear relationship is observed
(Figure 5d), however a much greater decrease is evident in the case when the bias is
varied as opposed to the writing speed.
These observations suggest that the nanopattern generated by this method depends
on the writing conditions i.e. writing speed and applied voltage. It should be mentioned
however that the mechanism of formation of these raised nanopatterns is not thoroughly
178
understood even though similar observation have been reported for poly(methyl
methacrylate) (PMMA) films. One theory is that the applied voltage increases the current
through the polymer underneath the conducting AFM tip.12
This increases the joule
heating of the polymer film. When the polymer film is heated and cross-linking of the
polymer chains occurs through electropolymerization, it is possible that thermal
expansion of the cross-linked materials give rise to the raised nanostructes.12
Figure 6.5. AFM topographic image of four lines pattern after (a) applying -10 V at
different writing speeds of 0.4, 0.6, 0.8, and 1.0 μm/s (from left to right) (b) a constant
writing speed of 0.4 μm/s at different voltage bias ranging from -10,- 8,- 6 to -4 V. (c)
Height profiles of four lines pattern after (c) applying -10 V at different writing speeds of
0.4, 0.6, 0.8, and 1.0 μm/s (from left to right) (d) a constant writing speed of 0.4 μm/s at
different voltage bias ranging from -10,- 8,- 6 to -4 V.
179
Although the AFM topography image determined using CS-AFM (contact mode)
have less resolution then images obtained using tapping mode, clearer images are
obtained from the current (Figure 6.6a and b) and the friction (see supporting
information) images. In these cases the patterns are better seen due to color scale (or
gray intensity) distribution.23
The higher contrast is due to the difference in conductivity
of the two materials with a high conductance corresponding to the cross-linked patterned
regions.23
Figure 6.6. AFM current maps of four lines pattern after (a) applying -10 V at different
writing speeds of 0.4, 0.6, 0.8, and 1.0 μm/s (from left to right) (b) a constant writing
speed of 0.4 μm/s at different voltage bias ranging from -10,- 8,- 6 to -4 V. (c) Current
profiles of four lines pattern after (c) applying -10 V at different writing speeds of 0.4,
0.6, 0.8, and 1.0 μm/s (from left to right) (d) a constant writing speed of 0.4 μm/s at
different voltage bias ranging from -10,- 8,- 6 to -4 V.
180
In addition to giving better resolution images, the raised line results in the
formation of electrically conducting nanopatterns due to the formation of extended -
conjugation of the terthiophene electroactive units via the electrochemical cross-linking
to form polyterthiophene.12e
This increased conductivity is confirmed through the current
map images (Figure 6.6a and b). For example, upon creating the patterns at different
writing speeds (Figure 6.6a) of 0.4, 0.6, 0.8 to 1.0 μm/s or voltage bias (Figure 6.6b) of
-10, -8, -6, and -4 V, the images were then processed by scanning the patterned areas with
an applied -3 V tip bias voltage at a rate of 1.5 lines/s. As seen in both cases, lower color
contrasts in areas where the lines were produced is evident. These areas imply the relative
differences in conductivity. For example Figure 6.6c shows the cross-sectional area of
the patterned lines produced at the different writing speeds of 0.4, 0.6, 0.8, and 1.0 μm/s
(left to right) at a constant -10 V bias. From the graphical representation the overall peak
intensities (current) of the patterned areas was 0.8, 0.6, 0.5, and 0.4 pA corresponding to
the line created at written at speeds of 0.4, 0.6, 0.8, and 1.0 μm/s, respectively. Similarly,
the cross-sectional area of the patterned lines produced at different voltages at-10, -8, -6,
and -4 V, were examined (Figure 6.6d) and the relative intensities corresponding to these
lines were 0.8, 0.7, 0.4, and ~ 0.0 pA, respectively.
Recently, CS-AFM has been used to probe site specific conductivity and I-V
properties of polyaniline (PANI) films by using current flow through an Au-coated
tip/PANI/ITO substrate.24
Similarly, Yang and co-workers have shown reversible
conductivity changes of a PANI composite film (nanofiber/gold nanoparticle ) using
conductive AFM.25
In this work Yang and co-workers emphasized the possible
181
Figure 6.7. AFM (a) topography (b) and current map of a single line created on
electroactive film at -10 V at writing speed of 0.4 m/s. (c) I-V curves of different
locations on the electroactive material.
182
application of nanoscale memory devices.25
Here as well, Yang and co-workers also
studied the conductivities of the pattern domains and their corresponding I-V responses in
order to better understand the mechanism of nanocharging in PEDOT.25
Herein, similar
results with the current polymeric film should reveal similar characteristics.
To test this a single line on the polymer brush film using a writing speed of 0.4
m/s and an applied bias of -10 V was performed. As seen from the AFM topography
(Figure 6.7a) and current (Figure 6.7b) images a distinct pattern was achieved. After
formation of the pattern, we obtained two current-voltage (I-V) curves (Figure 6.7c)
using two distinct areas on the current map image (Figure 6.7b), i.e. cross-linked
patterned (AFM tip positioned at arrow 1) and uncross-linked brush (AFM tip positioned
at arrow 2) areas. From the I-V curves several different characteristics were displayed.
First, in the case of arrow 1, this exhibited a typical junction, I–V curve of a conducting
polymer, indicating that the conductivity in the local region increased after nanowriting.
This observation presents good proof that the formation of conjugated polyterthiophene
patterned area contains many energy states within the band gap.12c,26
Compared with the
current image, the I-V curves gave a more quantitative sense with respect to the
conductivity change, although the conductivity values cannot be directly calculated from
this nonohmic behavior. In contrast, the unpatterned brush area (AFM tip positioned at
arrow 2) was depicted by a flat line in the I–V curve. This result is expected since this
area is composed of the unconjugated, uncross-linked brush.
183
Figure 6.8. AFM images of (a-c) three squares and (d-f) the state of Texas, where the
images correspond to the AFM (a and d) topography, (b and e) friction, and (c and f)
current images.
184
Finally, more complex patterns were drawn in order to demonstrate the facile
patterning on these types of electroactive polymer brush surfaces. Figure 6.8 shows the
2-D topographic (Figure 6.8a and d), friction (Figure 6.8b and e), and current (Figure
6.8c and f) images of a series of boxes (Figure 6.8a-c) and the state of Texas (Figure
6.8d-f) written at -10 V with a writing speed of 0.4 μm/s. The average height of the
pattern was determined to be 2.9 nm, which is consistent with the data presented earlier,
using the same patterning conditions. Similarly, higher resolution friction images were
also obtained (Figure 6.8b and e) so to further confirm the successful formation of the
two different patterns. Finally, the current images were also obtained again sweeping at -
3 V after patterning. It is clearly seen that the blue-green color contour showed a higher
current flow through the boxes (Figure 6.8c) and the state of Texas (Figure 6.8f)
patterns. In another words, the conductivity of the patterned areas are higher than the
unpatterned domains as mentioned earlier.
6.3 Conclusions
The fabrication of pendant terthiophene polymer brushes and their application as
ultrathin films have been demonstrated using the SIP approach. UV-vis, ellipsometry, and
AFM studies showed differences in the film structure at various stages of film
development. These films were subsequently employed for the investigation of
electrochemical nanopatterning using current sensing AFM as a writing technique. The
dependence of the nanofeature properties on applied voltage and writing speed was
185
studied. The pattern formation was demonstrated in order to show the possibility for
future applications such as information storage devices and nanowires.
6.4. Experimental Section
6.4.1. Materials
Reagent chemicals TBAH (99%), CuBr (99%), triethylamine (99%), bromine
(99%), and 2-(tributylstannyl)thiophene were purchased from Aldrich and were used
without further purification unless otherwise indicated. Chemicals trans-
dichlorobis9triphenylphosphine)palladium, ethyl thiophene-3-acetate (98%), and
terthiophene (99%) were purchased from Alfa Aesar and were used without further
purification. Deionized water, methanol (MeOH), dimethylformamide (DMF),
isopropanol, hexanes, ACN, and THF were used in the cleaning of ITO and gold slides,
synthesis, and polymerization reactions.
6.4.2. Surface Preparation
Substrates were first cut into 2.5 × 0.7 cm slides. The ITO slides were then
cleaned using an Alconix solution followed by sonicating in isopropanol, followed by
hexanes, and toluene for 10 min each. The ITO slides were then dried using N2 gas
followed by plasma cleaning for 3 minutes. Gold slides were rinsed with ethanol, dried
using N2 gas followed by plasma cleaning for 30 s. The slides were either used
immediately or stored in a desiccator.
186
6.4.3. Electrodeposition
The electropolymerization of the 3T-CTA was done using cyclic voltammetry
using an Autolab PGSTAT 12 potentiostat (Metro Ohm) in a standard three-electrode
measuring cell (a fabricated electrochemical cell with a diameter of 1.0 and volume of
0.785 cm3, made of Teflon) with platinum wire as the counter electrode, Ag/AgCl wire
as the reference electrode and the ITO substrate as the working electrode. All
electrodepositions were performed using CV in ACN using a potential of 0-1.2 V, a scan
rate of 50 mV/s, for 10 cycles. After the electrodeposition, the resulting film was washed
with ACN thrice.
6.4.4. Surface Initiated RAFT Polymerization
In a typical reaction SI-RAFT polymerization of 3T-Methacrylate was performed
as such. First 1.0 g (2.8 mmol) of 3T-Methacrylate and 0.77 g (4.7 X 10-3
mmol) of
azobisisobutyronitrile (AIBN) were dissolved in 8 mL of dry toluene and mixed using a
magnetic bar under N2 gas for 30 min. Afterwards 3 freeze-pump-thaw cycles were
performed on the mixture. The solution was transferred to a 2nd Schlenk tube contain the
coated gold or ITO substrate. Polymerization was performed for 72 hr at 80 oC.
Afterwards the slide was removed and carefully washed using toluene followed by THF.
The slide was dried with N2 and further dried in a vacuum desiccator before any further
measurements.
187
6.4.5. Synthesis of 3T-CTA
Synthesis of 3T-CTA was done according to previous literature.27
6.4.6. Synthesis of 3T-Methacyrlate
Synthesis of 3T-methacylate was done according to previous literature.20
6.4.7. Characterization
Atomic Force Microscopy (AFM) measurements were carried out in a piezo
scanner from Agilent Technologies. The scanning of the electropolymerized films were
performed under ambient and dry conditions. All AFM topographic images were filtered
and analyzed using SPIP (Scanning Probe Image Processor, Imagemet.com) or
Gwyddion 2.19 software. Cyclic voltammetry was performed in a conventional three-
electrode cell, using an Autolab PGSTAT 12 potentiostat (Brinkmann Instruments (now
MetroOhm USA)). The potentiostat was controlled using GPES software (version 4.9).
6.5 References
1. (a) Lutwyche, M. I.; Despont, M.; Drechsler, U.; Dürig, U.; Häberle, W.;
Rothuizen, H.; Stutz, R.; Widmer, R.; Binning, G. K.; Vettiger, P. Appl. Phys. Lett.
2000, 77, 3299. (b) Lawrence, J. R.; Andrew, P.; Barnes, W. L.; Buck, M.;
Turnbull, G. A.; Samuel, I. D. W. Appl. Phys. Lett. 2002, 81, 1955. (c) Huang, Y.;
Duan, X.; Wei, Q.; Lieber, C. M. Science 2001, 291, 630.
188
2. (a) Schneegans, O.; Moradpour, A.; Houzé, F.; Angelova, A.; de Villeneuve, C. H.;
Allongue, P.; Chrétien, P. J. Am. Chem. Soc. 2001, 123, 11486. (b) Mesquida, P.;
Knapp, H. F.; Stemmer, A. Surf. Interface Anal. 2002, 33, 159.
3. (a) Mamin, H. J.; Rugar, D. Appl. Phys. Lett. 1992, 61, 1003. (b) Binnig, G.;
Despont, M.; Drechsler, U.; Häberle, W.; Lutwyche, M.; Vettiger, P.; Mamin, H. J.;
Chui, B. W. Kenny, T. W. Appl. Phys. Lett. 1999, 74, 1329.
4. Piner, R. D.; Zhu, J.; Xu, F.; Hong, S.; Mirkin, C. A. Science 1999, 283, 661.
5. Tello, M.; García, R. Appl. Phys. Lett. 2001, 79, 424.
6. Baba, A.; Locklin, J.; Xu, R.; Advincula, R. J. Phys. Chem. B 2006, 110, 42.
7. Xie, X. N.; Chung, H. J.; Xu, H.; Xu, X.; Sow, C. H.; Wee, A. T. S. J. Am. Chem.
Soc. 2004, 126, 7665.
8. Stiévenard, D.; Fontaine, P. A.; Dubois, E. Appl. Phys. Lett. 1997, 70, 3272.
9. (a) Xie, X. N.; Chung, H. J.; Sow, C. H.; Bettiol, A. A.; Wee, A. T. S. Adv. Mater.
2005, 17, 1386. (b) Juhl, S.; Philips, D.; Vaia, R. A.; Lyuksyutov, S. F.; Paramonov,
P. B. Appl. Phys. Lett. 2004, 85, 3836.
10. Lyuksyutov, S. F.; Vaia, R. A.; Paramonov, P. B.; Juhl, S.; Waterhouse, L.; Ralich,
R. M.; Sigalov, G.; Sancaktar, E. Nat. Mater. 2003, 2, 468.
11. Maynor, B. W.; Filocamo, S. F.; Grinstaff, M. W.; Liu, J. J. Am. Chem. Soc. 2001,
124, 522.
12. (a) Jegadesan, S.; Advincula, R. C.; Valiyaveettil, S. Adv. Mater. 2005, 17, 1282.
(b) Jegadesan, S.; Sindhu, S.; Advincula, R. C.; Valiyaveettil, S. Langmuir 2006,
22, 780. (c) Jiang, G.; Baba, A.; Advincula, R. Langmuir 2007, 23, 817. (c) Huang,
189
C.; Jiang, G.; Advincula, R. Macromolecules 2008, 41, 4661. (d) Park, J. Y.;
Ponnapati, R.; Taranekar, P.; Advincula, R. C. Langmuir 2010, 26, 6167. (e) Park,
J. Y.; Taranekar, P.; Advincula, R. Soft Matter 2011, 7, 1849.
13. Tria, M. C. R.; Grande, C. D. T.; Ponnapati, R. R.; Advincula, R. C.
Biomacromolecules 2010, 11, 3422.
14. (a) Cha, T.; Guo, A.; Jun, Y.; Pei, D.; Zhu, X. Proteomics 2004, 4, 1965. (b)
Benhabbour, S.; Sheardown, H.; Adronov, A. Biomaterials 2008, 29, 4177.
15. Barbey, R.; Lavanant, L.; Paripovic, D.; Sch wer, N.; Sugnaux, C.; Tugulu, S.;
Klok, H. A. Chem. Rev. 2009, 109, 5437.
16. Perrier, S.; Takolpuckdee, P. J. Polym. Sci. Part. A 2005, 43, 5347.
17. Perrier, S.; Takolpuckdee, P.; Mars, C. A. Macromolecules 2005, 38, 2033.
18. (a) Sotzing, G.; Reynolds, J.; Steel, P. Chem. Mater. 1996, 8, 882. (b) Geissler, U.;
Hallensleben, M.; Rhode, N. Synth. Met. 1997, 84, 173.
19. Schrebler, S.; Grez, P.; Cury, P.; Veas, C.; Merino, M.; Gomez, H.; Cordova, R.;
del Valle, M. J. Electroanal. Chem. 1997, 430, 77.
20. Taranekar, P.; Fulghum, T.; Baba, A.; Patton, D.; Advincula, R. Langmuir 2007,
23, 908.
21. Kaneto, K.; Yoshino, K.; Inuishi, Y. Solid State Commun. 1983, 46, 389.
22. (a) Hiller, J.; Mendelsohn, J. D.; Rubner, M. F. Nat. Mater. 2002, 1, 59. (b) Cui, X.
D.; Primak, A.; Zarate, X.; Tomfohr, J.; Sankey, O. F.; Moore, A. L.; Moore, T. A.;
Gust, D.; Harris, G.; Lindsay, S. M. Science 2001, 294, 571. (c) Lee, J.;
Lientschnig, G.; Wiertz, F.; Struijk, M.; Janssen, R. A. J.; Egberink, R.; Reinhoudt,
190
D. N.; Hadley, P.; Dekker, C. Nano Lett. 2003, 3, 113. (d) Austin, M. D.; Chou, S.
Y. Nano Lett. 2003, 3, 1687.
23. Pernites, R. B.; Foster, E. L.; Felipe, M. J. L.; Robinson, M.; Advincula, R. C. Adv.
Mater. 2011, 23, 1287.
24. Wu, C. G.; Chang, S. S. J. Phys. Chem. B 2005, 109, 825.
25. Tseng, R. J.; Huang, J.; Ouyang, J.; Kaner, R. B.; Yang, Y. Nano Lett. 2005, 5,
1077.
26. Lee, H. J.; Park, S.-M. J. Phys. Chem. B 2004, 108, 1590.
27. Grande, C. D.; Tria, M. C.; Jiang, G.; Ponnapati, R.; Advincula, R. Macromolecules
2011, 44, 966.
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Chapter 7. Conclusions and Future Work
7.1. Conclusions
This dissertation has focused on the fabrication of electro-grafted coatings on
different conducting substrates in order to introduce a variety of different functional
groups to the surface. Electropolymerizability of macroinitiators, polymer-grafting
methods, reversible wetting behavior, controlled morphologies, and novel nanopatterning
methods have been demonstrated. Applications for this work were to prepare coatings for
controlled wetting behavior, dual surface chemistry, anti-corrosion, and the patterning of
electroactive molecules by colloidal templating and electrochemical nanolithography.
Chapter 1 gave an overview of electro-grafted and electroactive materials on
surfaces focusing primarily on surface initiated polymerization (SIP) from the grafted
coatings, superhydrophobic surface, and patterning methodologies. It also outlined the
methodologies and reaction routes used for the preparation of materials and surface
chemistry.
Chapter 2 demonstrated a facile approach of creating topologically and well-
defined patterned polymer brushes by combining the techniques of 2D colloidal sphere
templating, electrodeposition of a macroinitiator, and SIP via atom transfer radical
polymerization (ATRP), reversible addition fragmentation chain transfer (RAFT)
polymerization, and ring-opening metathesis polymerization (ROMP).
192
Chapter 3 demonstrated new approaches of creating topologically and well-
defined “clickable” colloidally templated arrays: the grafting chemistry can be performed
onto an electrodeposited pattern or by subsequent backfilling with azido terminated
SAM’s on templated conducting polymer arrays. Another approach enabled the
fabrication of ion gates by electro-grafting colloidally templated electroactive thermo-
responsive oligo(ethylene glycol)-methacrylic polymers.
Chapter 4 reported a novel one-step approach to fabricate superhydrophobic and
superoleophilic coating by using cyclic voltammetry (CV). Additional SI-ATRP of N-
isopropylacrylamide (NIPAM) or 3,3,4,4,5,5,6,6,7,7,8,8,9,9,10,10,10-
heptadecafluorodecyl methacrylate (HDFM) further resulted in interesting
superhydrophilic and oleophobic surfaces respectively.
In Chapter 5 tunable bacterial adhesion and self-cleaning properties were
demonstrated on a conducting superhydrophobic surface. By simply manipulating the
redox property of the conducting coating, the wettability of the surface was easily
changed, which drastically changed the adhesion of a biological agent. The current
system therefore, can be useful for fabricating smart coatings onto a variety of conducting
surfaces, in order to tune the resistance or adhesion of bacteria. Similarly, due to the
incorporation of an ATRP moiety within the superhydrophobic coating, SI-ATRP of
HDFM was performed on a steel slide. Subsequent static water, diiodomethane, and
hexadecane contact angles revealed that the steel-coated surface was now
superamphiphobic. We also demonstrated that the superhydrophobic steel coating could
193
have possible applications for corrosion prevention even without the need of either
fluorinated molecules or other toxic inorganic materials.
In chapter 6 the fabrication of pendant terthiophene (3T) polymer brushes and
their application as ultrathin films have been demonstrated using the SIP approach. UV-
vis, ellipsometry, and AFM studies showed differences in the film structure at various
stages of film development. These films were subsequently employed for the
investigation of electrochemical nanopatterning using current sensing AFM as a writing
technique. The dependence of the nanofeature properties on applied voltage and writing
speed was studied. The pattern formation was demonstrated in order to show the
possibility for future applications such as information storage devices and nanowires.
7.2. Future Work
The work presented in this research dissertation has led to a strong foundation in
the concept that electro-grafted materials can be used as viable and controllable surface
coatings. Besides forming robust films, electropolymerization offers an easy and facile
method to fabricate various functional thin films onto most conducting and electrode
substrates. Thus an important future direction of this work is to prepare libraries of
various functional and polymerizable electroactive monomers. Optimized thin films using
the fabrication and patterning methods described in this work will have promising
applications in biosensing, anti-corrosion coatings, and anti-biofouling. It is important to
understand the mechanism of the thin film formation, demonstrating control and spatial
organization of the functional groups on the substrate in order to tailor and optimize these
194
materials. This has been achieved in this dissertation. Although, we have carried out our
investigation in both the synthetic and materials development aspect, there is potential for
these materials in areas emphasizing the electro-optical properties of a conducting
polymer, e.g. electrochromism, charge carrier transport properties, redox properties, and
even non-linear optical properties. Thus, the design, development, and optimization of
new functional materials for various applications described in this dissertation will be an
ongoing process in our laboratory.
7.3. Final Remarks
Electro-grafting has proven to be an efficient and simple method to coat and or
functionalize conducting surfaces. The use of electro-grafting of surface coatings is of
tremendous interest for potential applications such as protein-resistant, corrosion
protection, surface patterning, sensors, and materials for scanning probe techniques. This
dissertation has demonstrated unique strategies to molecular design and novel fabrication
techniques for electrochemical deposition of polymeric films using functional
electroactive monomers.
195
Appendix I: Additional Information for Chapter 2
AP.I.1. Synthesis Methyl 3,5-bis(4-(9H-carbazol-9-yl)butoxy)benzyl Alcohol (Cbz-
OH) and 3,5-Bis[4-(9H-carbazol-9-yl)butoxy]benzoic Acid (Cbz-COOH)
The synthesis of Cbz-OH was performed according to literature and can be seen
in Scheme AP.I.1.1
Scheme AP.I.1. Synthesis of Cbz-OH and Cbz-COOH
196
AP.I.1.1. 9-(4-bromobutyl)-9H-carbazole (Cbz-Br)
The synthesis of Cbz-Br was done according to literature.1 The synthesis of Cbz-
Br was done by combining carbazole (20.64 g, 0.1236 mol), 1,4 dibromobutane (132 mL,
1.095 mol), tetrabutylammonium bromide (4 g, 0.0124 mol), toluene (200 mL), and 50%
NaOH (200 mL). The resulting mixture was stirred at 45 oC for 3 hrs and continuously
stirred at room temperature overnight. The clear, yellow organic layer was then washed
with 100 mL portions H2O followed by 100 mL brine solution. This was then dried over
anhydrous sodium sulfate (Na2SO4). The solvent was removed via rotary evaporator and
the excess 1,4-dibromobutane via vacuum distillation. After which, the resulting cream-
like solid residue was slowly dissolved in small portions of dichloromethane (DCM). The
yellow-brown solution was reprecipitated using ethanol. The resulting white solid residue
was dried under vacuum overnight to give 33.4 g (89%) of the product. 1H NMR (δ ppm
in CDCl3): 8.12 (d, 2H), 7.22-7.48 (m, 6H), 4.36 (t, 2H), 3.38 (t, 2H), 1.95-2.07 (m, 4H).
AP.I.1.2. Methyl 3,5-bis(4-(9H-carbazol-9-yl)butoxy)benzoate (Cbz-
COOCH3)
The synthesis of Cbz-COOH3 was done according to literature.1 The synthesis of
compound Cbz-COOCH3 was done by combining Cbz-Br (27.9 g, 0.0923 mol), methyl-
3,5-dihydroxybenzoate (6.49 g, 0.0386 mol), and 18-crown-6 (2.41 g) in acetone. To the
resulting yellow solution mixture was added potassium carbonate (K2CO3) (29.5 g) and
this was left at reflux for 3 days. The solvent was then removed using a rotary evaporator.
Water was added to the cream solid residue and the desired compound extracted with
197
dichloromethane. The organic layer was subjected to rotary evaporation until 20-25 mL
was left just to dissolve the solid residue. To this was added ethyl acetate to precipitate
out the desired white solid compound in 70 % yield. 1H NMR (δ ppm in CDCl3): 8.20 (d,
4H), 7.49-7.12 (m, 16H), 6.54 (s, 1H), 4.40 (t, 4H), 3.95 (t, 4H), 3.88 (s,3H) 2.11-2.04
(m, 4H), 1.87-1.82 (m, 4H).
AP.I.1.3. Cbz-OH
The synthesis of Cbz-OH was done according to literature.1 The synthesis of
compound Cbz-OH was carried out by first dissolving Cbz-COOCH3 (10.5 g, 0.01719
mol) in dry THF. Into a 3-necked flask flowed with nitrogen was placed 100 mL THF
and this was cooled in an ice bath. Approximately 1 g LiAlH4 was put into the flask and
the Cbz-COOCH3 solution added dropwise through a dropping funnel. The resulting
mixture was then stirred overnight. After which, the reaction was quenched by adding
water until all LiAlH4 was consumed. This was then acidified using concentrated HCl
and extracted with DCM. The organic layer was further washed with water for several
times and then dried with Na2SO4. The DCM was evaporated using a rotary evaporator
and the desired white solid compound was further dried under vacuum 90 % yield. 1H
NMR (δ ppm in CDCl3): 8.09 5 (d, 4H, J = 7.5 Hz), 7.47-7.18 (m, 12H), 6.43 (s, 2H),
6.27 (s, 1H), 4.57 (d, 2H, J = 5.7 Hz), 4.38 (t, 4H, J = 6.9 Hz), 3.90 (t, 4H, J = 5.9 Hz),
2.09-2.01 (m, 4H), 1.84-1.79 (m, 4H).
198
AP.I.1.4. Cbz-COOH
The synthesis of Cbz-COOH was done according to literature.2 A mixture of Cbz-
COOCH3 (3.00 g, 4.91 mmol) and KOH (2.76 g, 49.12 mmol) in
tetrahydrofuran/methanol (30 ml/60 ml) was refluxed with vigorous stirring for
overnight. After cooling to room temperature, the mixture was concentrated to dryness
under reduced pressure. The residue was acidified to pH 2-3 with HCl, and then the
precipitate was filtered and washed with ether to afford a white solid (2.76 g, 94 % yield).
1H NMR (δ ppm in CDCl3): 8.09 (d, 4H, J = 7.8 Hz), 7.84-7.39 (m, 8H), 7.24-7.17 (m,
4H), 7.16 (s, 2H), 6.57 (s, 1H), 4.40 (t, 4H, J = 6.3 Hz), 3.94 (t, 4H, J = 6.0 Hz), 2.08 (m,
4H), 1.84 (m, 4H) ppm.
AP.I.2. 3,5-bis(4-(9H-carbazol-9-yl)butoxy)benzyl 2-bromo-2-methylpropanoate
(Cbz-Initiator)
The synthesis of Cbz-Initiator was performed according to literature and can be
seen in Scheme I.2.3 In a round bottom flask both Cbz-OH (338 mg, 0.58 mmol) and
triethylamine (TEA) (58.4 mg, 0.58 mmol) were added along with 50 ml of dry THF. A
solution of 2-bromoisobutyryl bromide (133 mg, 0.58 mmol) in 10 ml dry THF was
added dropwise to the mixture under constant stirring. The reaction was allowed to
proceed overnight. The reaction mixture was then filtered to remove the white solid
byproduct. The organic phase was extracted 3 times with H2O and dried over anhydrous
Na2SO4. The solvent was removed under vacuum. The crude product mixture was first
then purified by column chromatography on silica gel with DCM:hexane (2:1, v/v). The
199
solvent was removed by rotary evaporation to yield Cbz-Initiator as a white solid (0.36 g,
86%). 1H NMR (δ ppm in CDCl3): 8.09 (d, 4H, J = 7.5 Hz), 7.47-7.18 (m, 12H), 6.45 (s,
2H), 6.32 (s, 1H), 5.10 (s, 2H), 4.38 (t, 4H, J = 6.9 Hz), 3.90 (t, 4H, J = 5.9 Hz), 2.09-
2.01 (m, 4H), 1.94 (s, 6H), 1.84-1.79 (m, 4H). 13C (δ ppm in CDCl3): 171.5, 161.2,
140.4, 137.5, 125.8, 122.9, 120.5, 118.9, 108.7, 106.0, 101.23, 67.7, 67.4, 55.9, 42.8,
30.9, 27.0, 26.0. Anal. Calcd for C43H43BrO2N4: C, 70.58; H, 5.92; Br, 10.92; N, 3.83.
Found: C, 70.51; H, 6.03; Br, 10.80; N, 3.80.
Scheme AP.I.2. Synthesis of Cbz-Initiator
AP.I.3. Synthesis of 3,5-bis(4-(9H-carbazol-9-yl)butoxy)benzyl-4-cyano-4
(phenylcarbonothioylthio)pentanoate (Cbz-CTA)
The synthesis of Cbz-CTA was performed according to literature and can be seen
in Scheme AP.I.3.4
A solution of Cbz-OH (0.78 g, 1.34 mmol), 4-Cyano-4-
((thiobenzoyl)sulfanyl)-pentanoic acid (0.401 mg, 1.44 mmol), and 4-(dimethylamino)
pyridine (DMAP) (25 mg, 0.20 mmol) was dissolved in anhydrous DCM (15 mL) under
200
N2. Dicyclohexylcarbodiimide (DCC) (412 mg, 2.0 mmol) in 5 mL of DCM was added
dropwise to the reaction mixture at 0 °C. The reaction was stirred vigorously at 0 °C for 5
min and then warmed to room temperature and stirred overnight. The reaction mixture
was filtered to remove the white solid byproduct. The organic phase was washed and
dried over anhydrous Na2SO4, and the solvent was removed under vacuum. The crude
product mixture was first washed with ethyl acetate and then purified by column
chromatography on silica gel with DCM:hexane (4:1, v/v). The solvent was removed by
rotary evaporation to yield Cbz-CTA as a pink-orange solid (0.79 g, 70%). 1H NMR (δ
ppm in CDCl3): 8.13 (d, 4H); 7.88 (d, 2H); 7.6-7.24 (m, 15H); 6.48 (s, 2H); 6.37 (s, 1H);
5.08 (s, 2H); 4.40 (t, 4H,); 3.92 (t, 4H); 2.76-2.40 (m, 4H); 2.12-2.00 (m, 4H); 1.92-1.76
(m, 7H).
Scheme AP.I.3. Synthesis of Cbz-CTA
201
AP.I.4. Synthesis of Bicyclo[2.2.1]hept-5-en-2-yl-methyl 3,5-Bis- (4-(9H-carbazol-9-
yl) butoxy)benzoate (Cbz-Nb)
The synthesis of Cbz-Nb was performed according to literature and can be seen in
Scheme AP.I.4.5 In a 100 mL round-bottom flask equipped with a stir bar and an
addition funnel, a solution of Cbz-COOH (1.93 g, 3.23 mmol), 5-norbornene- 2-methanol
(0.48 g, 3.88 mmol), and DMAP (40 mg, 0.323 mmol) in 40 mL of dry DCM was cooled
to 0 oC under N2. DCC (0.800 g, 3.88mmol) was dissolved in 10 mL of DCM and added
dropwise to the reaction flask under stirring. After complete addition of DCC, the
reaction was stirred for 10 min at 0 oC and then allowed to stir at room temperature
overnight. Then, the white solids were removed by gravity filtration, and the filtrate was
washed with dilute sodium bicarbonate (40 mL) and water (2 X 30 mL) and finally dried
over anhydrous Na2SO4. The solution was filtered, and the solvent was removed to yield
the white crude product mixture, which was further purified by column chromatography
on silica gel using 4:1 DCM/hexane as the eluent. The final yield was 1.58 g (69.6%). 1H
NMR (δ ppm in CDCl3): 8.15 (d, 4H, J = 7.8 Hz),7.39-7.57 (m, 8H), 7.20-7.34 (m, 6H),
6.60 (t, 1H, J = 2.1 Hz), 6.25 (q, 0.6 H, J = 3.0 Hz), 6.17 (m, 0.8H), 6.06 (q, 0.6 H, J =
3.0 Hz), 4.46 (dd, 0.5H, J = 6.9 Hz),4.37 (t, 4H, J = 6.9 Hz), 4.27 (t, 6H, J = 10.5 Hz),
3.94 (t, 4H, J = 5.7 Hz ), 3.03 (s, 6H), 2.90 (s, 9H), 2.86 (s, 0.4H), 2.08 (m, 4H), 1.86 (m,
5H), 1.42 (m, 3H), 1.00 (m, 2H), 0.70 (m, 6H).
202
Scheme AP.I.4. Synthesis of Cbz-Nb
AP.I.5. Synthesis of 11-(2-bromo-2-methyl)-propionyloxy)-undecyl-trichlorosilane
(ATRP-Silane)
The synthesis of ATRP-Silane was done according to literature and is shown in
Scheme AP.I.5.6
Scheme AP.I.5. Synthesis of ATRP-Silane
AP.I.5.1. 10-Undecen-1-yl 2-Bromo-2-methylpropionate (ATRP-Olefin)
To a solution of 4.257 g (25 mmol) of -undecylenyl alcohol in 25 mL of dry
tetrahydrofuran was added 2.1 mL of TEA (26.5 mmol) followed by dropwise addition of
3.10 mL of 2-bromoisobutyryl bromide (25 mmol). The mixture was stirred at room
203
temperature overnight and then diluted with hexane (50 mL) and washed with 2 N HCl
and twice with water. The organic phase was dried over sodium sulfate and filtered. The
solvent was removed from the filtrate under reduced pressure, and the colorless oily
residue was purified by column chromatography (hexane) to give 7.34 g (92%) of the
ester as a colorless oil. 1H NMR (δ ppm in CDCl3): 1.22-1.45 (m, 12H); 1.62-1.75 (m,
2H); 1.94 (s, 6H); 2.05 (q, 2H, J = 6 Hz); 4.17 (t, 2H, J = 9 Hz); 4.9-5.05 (m, 2H); 5.72-
5.9 (m, 1H).
AP.I.5.2. ATRP-Silane
To a dry flask were added 1.35 g (4.23 mmol) of ATRP-Olefin and 4.2 mL of
trichlorosilane (42.6 mmol), followed by the addition of Karstedt catalyst (4 L). The
solution was quickly filtered through a plug of silica gel to remove the catalyst. The
excess reagent was removed by vacuum distillation. 1H NMR (δ ppm in CDCl3): 1.23-
1.45 (br m, 16H); 1.54-1.75 (m, 4H); 1.93 (s 6H); 4.16 (t, 2H, J ) 9 Hz).
AP.I.6. References
1. Taranekar, P.; Fulghum, T.; Patton, D.; Ponnapati, R.; Clyde, G.; Advincula, R. J.
Am. Chem. Soc. 2007, 129, 12537.
2. Kaewtong, C.; Jiang, G.; Felipe, M. J.; Pulpoka, B.; Advincula, R. ACS Nano 2008,
2, 1533.
3. Foster, E. L.; Tria, M. C. R.: Pernites, R. B.; Addison, S. J.; Advincula, R. C. Soft
Matter 2012, 8, 353.
204
4. Patton, D.; Taranekar, P.; Fulghum, T. Advincula, R. Macromolecules 2008, 41,
6703.
5. Jiang, G.; Ponnapati, R.; Pernites, R.; Grande, C. D.; Felipe, M. J.; Foster. E.;
Advincula, R. Langmuir 2010, 26, 17629.
6. Yu. K.; Wang, H.; Xue, L.; Han, Y. Langmuir 2007, 23, 1443.
205
Appendix II: Additional Information for Chapter 3
AP.II.1. Synthesis of 3,5-Bis[4-(9H-carbazol-9-yl)butoxy]benzoic Acid (Cbz-COOH)
The synthesis of Cbz-COOH was performed according to literature and is also
shown in Appendix I.1
AP.II.2. Synthesis of 2-(2-hydroxyethoxy)ethyl 3,5-Bis(4-(9H-carbazol-9-
yl)butoxy)benzoate (Cbz-TEG), and prop-2-ynyl 3,5-Bis(4-(9H-carbazol-9-
yl)butoxy)benzoate (Cbz-Alkyne)
The synthesis of Cbz-TEG and Cbz-Alkyne were performed according to
literature and can be seen in Scheme AP.II.1.1,2
206
Scheme AP.II.1. Synthesis of Cbz-TEG and Cbz-Alkyne
AP.II.2.1 Synthesis of Cbz-TEG
In a one-necked flask were combined Cbz-COOH (100 mg, 0.17 mmol),
tetraethylene glycol (97.5 mg, 0.50 mmol), and 4-dimethylaminopyridine (DMAP) (2.90
mg, 0.02 mmol). The mixture was dissolved in minimal amount of dichloromethane,
bubbled with nitrogen, and placed in an ice bath. After which, a solution of
dicyclohexylcarbodiimide (DCC) (47.9 mg, 0.23 mmol) in dichloromethane (DCM) was
207
added dropwise to the reaction mixture. This was then stirred vigorously for 30 mins,
warmed to room temperature and stirred for 2 days. The solid by-product was filtered off
and the filtrate was washed with water (5x) and brine solution (2x). The mixture was then
subjected to column chromatography using 3% MeOH/DCM. The desired product was
further purified by precipitating out other by-products with ethyl acetate. The supernatant
was then concentrated and dried under vacuum. 1H NMR (δ ppm in CDCl3): 8.19 (d, 4H,
J = 7.8 Hz), 7.56-7.49 (m, 8H), 7.35-7.29 (m, 4H), 7.24 (d, 2H, J = 2.4 Hz), 6.63 (t, 1H, J
= 2.7 Hz), 4.55 (t, 2H, J = 4.8 Hz), 4.48 (t, 4H, J = 6.6 Hz), 4.03 (t, 4H, J = 6.0 Hz), 3.89
(t, 2H, J = 4.8 Hz), 3.78-3.61 (m, 12H), 2.22-2.12 (m, 4H), 1.97-1.88 (m, 4H).
AP.II.2.2 Synthesis of Cbz-Alkyne
In a one-necked flask were combined Cbz-COOH (1.0 g, 1.7 mmol), propargyl
alcohol (190 mg, 3.4 mmol), and DMAP (21 mg, 0.17 mmol). The mixture was dissolved
in 50 ml of DCM, bubbled with nitrogen, and placed in an ice bath. After which, a
solution of DCC (700 mg, 3.4 mmol) in DCM was added dropwise to the reaction
mixture. This was then stirred vigorously for 30 mins, warmed to room temperature and
stirred overnight. The solid by-product was filtered off and the filtrate was washed with
water (2x) and brine solution (2x). The mixture was then subjected to column
chromatography using 1/4 hexanes/DCM (72% yield). 1H NMR (δ ppm in CDCl3): 8.19
(d, 4H, J = 7.8 Hz), 7.56-7.49 (m, 8H), 7.35-7.29 (m, 4H), 7.24 (d, 2H, J = 2.4 Hz), 6.63
(t, 1H, J = 2.7 Hz), 5.29 (d, 2H, J = 2.3 Hz), 4.55 (t, 2H, J = 4.8 Hz), 4.48 (t, 4H, J = 6.6
Hz), 4.03 (t, 4H, J = 6.0 Hz), 3.89 (t, 2H, J = 4.8 Hz), 3.78-3.61 (m, 12H), 2.49, (t,1H, J
208
= 2.3 Hz), 2.22-2.12 (m, 4H), 1.97-1.88 (m, 4H); 13
C NMR (δ ppm in CDCl3): 165.71,
160.09, 140.52, 131.34, 125.89, 123.04, 120.39, 119.08, 108.84, 108.14, 106.94, 77.92,
75.38, 67.93, 52.78, 42.77, 27.07, 25.94.
AP.II.3. Synthesis of 9-Azidononane-1-thiol
The synthesis of 9-azidoundecane-1-thiol was performed according to literature.3
AP.II.4. References
1. Pernites, R. B.; Felipe, M. J. L.; Foster, E. L.; Advincula, R. C. ACS Appl. Mater.
Interfaces 2011, 3, 817. (b) Pernites, R. B.; Foster, E. L.; Felipe, M. L.; Robinson,
M.; Advincula, R. C. Adv. Mater. 2011, 23, 1287.
2. Foster, E. L. Bunha, A.; Advincula, R. Polymer 2012, 53, 3124.
3. Collman, J. P.; Devaraj, N. K.; Chidsey, C. E. D. Langmuir 2004, 20, 1051.
