2) Stimuli 2) Stimuli responsiveresponsive polyelectrolytepolyelectrolyte coatingscoatings

Samuel Dodoo, Anna Burmistrova, Kornelia Gawlitza, Adrian Carl, Marcel Richter, Regine v. Klitzing

Stranski-LaboratoriumTechnical University of Berlin, Germany

Polymer coatings: MotivationPolymer coatings: Motivation

Nano- and Mesoscopic polymer films (thickness: 1 – 1000 nm)External stimuli: temperature, ionic strength, pH, humidity …

Sensitivity <=> Stability

Design and characterisationof stimuli responsive

surface coatings

CH3 CH3

OCH3

N*

N+

*

Cl

n

m

CH3

**

SO 3

n

Na+-

**

NH3

n

Cl+

*

n

OR

OO

OR

OOO

OROR

OR

OR

R=COO-Na+

Decher, G.; Hong, J.D.; Schmitt, J. Thin Solid Films 1992, 210, 831.

OR

OO

OH

OO

OHOH

CH2 OH

CH2OCH2CH2OH

O(CH2CH2O)2

CH2CHCH2

OH

N+

CH3

CH3

CH3

Cl

Polycations Polyanions

JR400

PAH

CMC

P(DADMAC-NMVA)

PSS

HA

LayerLayer--byby--layer techniquelayer technique

1) Ion 1) Ion specificspecific EffectsEffects

=> Increasing interaction between anions and polycations

0 2 4 6 8 10 12

0

100

200

300

400

500

600

700

Cl-

F-

Thic

knes

s, d

/ Å

Number of layers, N

Br-

Ion specific effects: Effect of anionsIon specific effects: Effect of anions

Increasing ion diameter (decreasing hydration shell)

PSS/PDADMAC

[NaX]=0.25mol/l Si

coiled

dBr-Br-

Br- Br-

Si

flatd

F-

F-

F-

J.E. Wong, R.v.K, Macromolecules, submitted

Ion specific effects:Ion specific effects: AFM studiesAFM studies

(PSS/PDADAMAC)6 prepared in 0.25 mol/l salt

NaCl

RMS 15 Å

CsClNaBr

25 Å 21 Å

Increasing roughness

with increasing ion size

J.E. Wong, R.v.K, Macromolecules, accepted

Different types of multilayer growingDifferent types of multilayer growing

0 2 4 6 8 10

thic

knes

s

number of layers

Kovacevic et al., Langmuir, 2002Biesheuvel et al. Langmuir, 2004Garza et al. , Langmuir 2004

-+-+-+-

+Si

linear

Different types of multilayer growingDifferent types of multilayer growing

0 2 4 6 8 10

thic

knes

s

number of layers

Kovacevic et al., Langmuir, 2002Biesheuvel et al. Langmuir, 2004Garza et al. , Langmuir 2004

-+-+-+-

+Si

linear

exponential

Different types of multilayer growingDifferent types of multilayer growing

0 2 4 6 8 10

thic

knes

s

number of layers

Kovacevic et al., Langmuir, 2002Biesheuvel et al. Langmuir, 2004Garza et al. , Langmuir 2004

-+-

+Si

2 4 6 8 10 120

100

200

300

400

500

600

700 100%, 0.1 mol/l 75%, 0.1 mol/l

th

ickn

ess

/ Å

number of adsorbed layers

Preparation in NaBr, 2 different PDADMAC charge densities

Effect of degree of chargeEffect of degree of charge

2 4 6 8 10 120

100

200

300

400

500

600

700 100%, 0.1 mol/l 75%, 0.1 mol/l 100%, 0.25 mol/l

th

ickn

ess

/ Å

number of adsorbed layers

Preparation in NaBr, 2 different PDADMAC charge densities

Effect of ionic strengthEffect of ionic strength

Transition from linear to exponential increase by increasing ionic strength

2 4 6 8 10 120

100

200

300

400

500

600

700 100%, 0.1 mol/l 75%, 0.1 mol/l 100%, 0.25 mol/l 75%, 0.25 mol/l

th

ickn

ess

/ Å

number of adsorbed layers

Preparation in NaBr, 2 different PDADMAC charge densities

Effect of degree of chargeEffect of degree of charge

Effect of polymer charge density on the type of growth

2 4 6 8 10 120

100

200

300

400

500

600

700 75%, 0.25 mol/l NaBr

th

ickn

ess

/ Å

number of adsorbed layers

Effect of type of saltEffect of type of salt

2 4 6 8 10 120

100

200

300

400

500

600

700 75%, 0,25 mol/l NaBr 75%, 0,25 mol/l NaCl

th

ickn

ess

/ Å

number of adsorbed layers

Comparison NaBr <-> NaCl

Tuning of type of growth by changing salt during preparation

Effect of type of saltEffect of type of salt

)Dtx(

πDtMC(x,t)

4exp

2

2−=

Deposition of the probing layer

O

O

O

NH

O OH

SC

**

NH3

m *

*

NH3

n

-20 -10 0 10 2020

40

60

80

100

120

140

160 after bleaching after treatment

Gre

y va

lue

/a.u

.

Distance/µm

Mobility: Fluorescence Recovery after Mobility: Fluorescence Recovery after PhotobleachingPhotobleaching (FRAP)(FRAP)

Polyanion/polycation D / cm2/sPSS/PAH < 10-15

PSS/PDADMAC 10-14

PSS/PDADMAC (75 %) 10-13

PSS/PDADMAC (NaBr) 10-13

HA/PDADMAC 10-11

FITC-PAH

P. Nazaran, R.v.K. et al. J. Phys. Chem B (2007)

Internal structure: Exposure to high ionic strengthInternal structure: Exposure to high ionic strength

0 2 4 61E-5

1E-4

1E-3

0.01

0.1

1

0.4 0.8 1.2 1.6 2.0 2.4 2.8

1E-4

1E-3

0.01

D2O 1M NaCl 3M NaCl 4M NaCl

Ref

lect

ivity

tth / deg

tth / deg

Ref

lect

vity

silicon substrate

td

Si/PEI/[(PSS/PAH)2/d-PSS/PAH]6

0 1 2 3 4

1.00

1.02

1.04

1.06 t d

Nor

mal

ized

thic

knes

s

NaCl concentration / M

⇒ Film swelling for cNaCl ≥ 3 M⇒ Non-homogeneous swelling

R. Steitz, R.v.K. (Adam, ILL Grenoble)

Swelling: Swelling: ““freefree”” water vs. water vs. ““voidvoid”” water (neutron water (neutron reflectometryreflectometry))

d2/d1 φfree φvoid φtotal

(PSS/PDADMAC)9 1.79 0.44 0.10 0.54

(PSS/PAH)9 1.60 0.38 0.11 0.49

(PSS/PAH)9/PSS 1.57 0.36 0.10 0.46

d1

D2O liquid or vapor

d2

φfree

φvoid

Silicon substrate

d1

vacuum

S. Dodoo, J.E. Wong, R. Steitz, R.v.K.

Swelling in water: Effect of preparation parametersSwelling in water: Effect of preparation parameters

S. Dodoo, R. Steitz, R.v.K.

0,2

0,3

0,4

0,5

0,6 0.10 M 0.25 M 0.50 M

wat

er c

onte

nt

NaF NaCl NaBr

(PSS/PDADMAC)6

Addition of different amount and type of salt during preparation

=> Increasing water content with increasing ionic strength

and increasing anion polarizibility

Intrinsically compensatedLess mobile (Glassy)Lower amount water

Low Ionic strengthChloride ion100% charged PE

High Ionic strengthBromide ion75% charged PE

Extrinsically compensatedMore mobile (Liquefied)Higher amount of water

Conclusion: ion specific effectsConclusion: ion specific effects

Treatment:Dissolution of complexes byIncreasing ionic strength (stronger for bromide)

Preparationconditions

2) 2) TemperatureTemperature effectseffects

Temperature induced increase in the mobility:

Transition from a glassy state to a swollen and liquefied structure accompanied with softening of the film.

0 .1M N aC l 1M N aC l 0 .1M N aB r 1M N aB r10 -15

10 -14

10 -13

10 -12

Ion ic cond ition o f film p repa ra tion

Diff

usio

n co

effic

ient

/ cm

²/sec

R oom tem p. 65° C

Effect of heatingEffect of heating

(PSS/PDADMAC[75%)])6 against water

DADMAC

N+

CH3CH3

Cl

Na-SS

Na+

SO3

O NH

CH3CH3

NIPAM

O NH

CH3CH3

SO3 H+

AMPS

OO

N

CH3CH3

+

DEAEM

• Block-copolymers

• statistical copolymers

EffectEffect of of chargecharge distributiondistribution: : NIPAMNIPAM--copolymerscopolymers

U. Voigt, V. Khrenov, K. Tauer, M. Hahn, W. Jaeger, R. v.K., J. Phys: Condens. Matter (2003)

0,00 0,02 0,04 0,06 0,0810-4

10-3

10-2

10-1

100

101

102

103

104

20 °C 40 °C 50 °C 60 °C

I/I0

Q [Å-1]

-100 0 100 200 500 600

2

3

4

5

6

7

D2O

Si

20 °C 40 °C 50 °C 60 °C

Nb

x 10

-6 [Å

-2]

z [Å]

Neutron reflectometry at solid/liquid interface: (PSS-b-PNIPAM/PDADMAC)n

Small decrease in thickness

Irreversible shrinking process

Irreversible annealing of the film

=> Strong interdigitation

10 20 30 40 50 60560

565

570

575

580

585

590

595

600

Film

thic

knes

s [Å

]

Temperature [°C]

R. Steitz, V. Leiner, K. Tauer, V. Khrenov, R.v.K. Appl. Phys. A (2002)

Effect of temperature on solvent swollen films Effect of temperature on solvent swollen films - +

Stimuli responsive coatings Stimuli responsive coatings

Strategy: Formation of stimuli-repsonsive coating by adsorption of microgel particles

=> Effect of geometrical confinement on sensitivity

ΔT ΔpH?

in bulk at interfaces

? ΔpH, ΔT

Hydrogel microparticles

Control of Control of hydrogelhydrogel particle densityparticle density

Explanation for 2D pattern: • Capillary attraction vs. dipolar repulsion• Shrinking of swollen (single) particles

After spin coating, pH 2

After rinsingin pH 2

S. Schmidt, T. Hellweg, H. Motschmann, R. v. K. Polymer (2008)

P(NIPAM-co-AA) particles on Si/PEI

0,2 0,4 0,6 0,8 1,0 1,2

1E-4

1E-3

0,01

0,1

1

0,4 0,5 0,6

0,01

0,02

0,03

0,04

Ref

lect

ivity

theta / deg

25°C 40°C 25°C

Ref

lect

ivity

theta / deg

Swelling / shrinking of Swelling / shrinking of hydrogelhydrogel particlesparticles

Neutron reflectometry => reversibility

(HMI 2006)

P(NIPAM-co-AA) particles (pH = 2)Ellipsometry => decrease in LCST

25°C, air 25°C, H2O 55°C, H2OSFM (amb./liquid) => Compactisation (T > LCST)

400 nm: 90% D2O200 nm: 80% D2O

15 μm

S. Schmidt, T. Hellweg, H. Motschmann, R. v. K. Polymer (2008)M. Karg, T. Hellweg, R.v.K. et al. Langmuir (2008) S. Schmidt, T. Hellweg, R.v.K., Langmuir (2008)

Fresh from the labFresh from the lab: Fluctuation length close to phase transition: Fluctuation length close to phase transition

GISANS (D16, ILL Grenoble)6.-17.11.2008

15 20 25 30 35 40 45 50 55 600

1

2

3

4

ξ / n

mT / °C

M. Medebach, R.v.K., Cooperation: P. Müller-Buschbaum, TU Munich

=> Increase in fluctuation length ξ close to Tc

Tc

P(NIPAM-co-AA) particles on Si/PEI (pH = 6)

Ornstein Zernike => fluctuation length ξ

Zone close to the surface

remains unaffected

Conclusion: Temperature sensitivityConclusion: Temperature sensitivity

Polyelectrolyte multilayers:

•Sensitivity to temperature rather low due to

interdigitation

Thermosensitive coatings by adsorption of hydrogel microparticles

• Control of particle density

• Reversible shrinkage and swelling

• Small shift of the LCST to lower temperature

• Unchanged interphase between solid surface

and „continuum“ of the particle

ΔT

-+-+-+-

+Si

New strategies for embedded biocatalysts:• Stabilisation of catalyst• Selective permeability• Easy separation• Fast response to external stimuli

Current projectsCurrent projects

Cooperation:CoE „Unicat“ (Berlin-Potsdam):M. Ansorge-Schumacher TU BerlinH. Möhwald MPI-KG, PotsdamRainer Haag, FU Berlin

Self-assembly at interfaces (bottom up)

GISANS: new set-up

at ISIS (BMBF project)

Patterned surfaces

10 – 50 nmhν (VIS)

Actuation by lightAu particles

(-> Photovoltaics)