Morphological Studies of Polymer Blends by
Scanning Tunneling Microscopy:
Phase Separation in Poly( methyl methacrylate ) /
Poly( styrene-CO-methylmethacrylate ) Systems.
by
Shakour Ghafouri-Bakhsh
A thesis submitted in conformity with the requirements for the
Degree of Master of Science
Griiduate Department of Chernistry. University of Toronto
O Copyright by Shakour Ghafouri-Bakhsh 1994
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Abstract
Morphological Studies of Poly mer Blends by Scanning Tunneling
Microscopy: Phase Separation in Poly( methylmethacrylate ) / Poly(
styrene-co-methylmethacrylate ) Systems.
Degree of Master of Science 1994
S hakour Ghafouri-Bakhsh
Gmduate Dupamient of Chernistry, University of Toronto
In ihis work. a ncw approach based on ihe scanning tunnelhg microscopy (STM) technique was
developcd to study the inorphology of the phases in irnmiscible polymer blends. The miid operathg
conditions of the STM Jlow one to image samples that decompose under electron beam in the eîectfon
microscope. Blends of PMMA / ply( Stx-co-MMA ) with different compositions of copolymer in the
biend ($). and styrenc in the copolymer (x), were studied. Microtomed surfaces of the samples were made
conductivc by gold coating. The rcsolution of the STM technique in this approach is Iïmited to the size of
Lhe gold grains (20 nm). Good STM images were obtauied f a ail of the opaque samples. sotne of which
werc impossible to imrigc with the elecuon microscope. Samples with x = 0.8 showed cocontinuous
morphology for 0.3<$4.50. dispcrsed phase morphology for w0.2 and +>0.6. and percolauon limits at 4
= 0.2 and = 0.6. The avcngc size of the disperscd phase for = 0.8 and I$ = 0.9 was found to be 520 nrn
and 340 nm for x=0.8. ,and 170 nm and 150 nm for x = 0.50. respectively. in another approach, samples
of 200 nrn thickncss wcrc imagcd by the scanning elecuon microscopy (SEM) after enhancement of phase
contnst by m a s of ctcctron h a n wtüch decomposed the PMMA phase. This approach gave good results
onIy for thc svnpies with ovctllll styrcne contents of mon: than 408. The turbidity of the samples was
found tu bc clcarly cornlaicd wiih the sizes of ihe features of ihe separateci phases.
Acknowledgments
First, I want to express my best gratitude and respect to professor G. Julius
Vancso, my supervisor, who taught me the delicacies of scientific work. The scientific
standing of professor Vancso, together with his wisdom in advising, sincereness in
helping. and his patience and tolerance in dealing with the students who have
communication weaknesses, are the characteristics that make hirn a truly outstanding
acadernic supervisor.
Second, 1 extend my deep thanks to professor Ulrich Kmll, who helped me to
resume my praduate studies. 1 have benefited from his enthusiasm in teaching on many
occasions, in his classes and during our nurnerous discussions. Especially I thank him for
his genervsity in letting me use his lab facilities for my study and practice More this
graduate work.
1 appreciate professor B. Pukanszky and his group in CRIC, Hungary for their supplying of the pcdymeric materials used in this thesis work. They also provided the
unpublished results of the mechanical and opticd characterization of the samples. Also I want tci acknowledge the contribution of Dr. G. P. Hellmann fkom DU, Germany, who
initiated the comprehensive research work, a part of which became the basis for the
present thesis.
1 am thankful to Mr. Fred Neub from the Department of Materials Science who
helped and taught me how to image with the electron microscope. I also appreciate the
work of Miss. Charlene Ng, the youngest member of the group, who successfully set up
and employed the Burleigh ISTM, before it was used for this work. 1 thank Guobin Liu
who ran the DSC instrument to obtain the glass transition temperature of my sarnples. I
also thank Paul Smith, who scanned some of my sampies with the tapping mode AFM,
and Daisy Da Silva who provided the facilities of her computer lab. Finaily, 1 would like to
express my special thanks to Ms. Anne Klemperer for reading the final version of this
thesis and for her useful suggestions in correcting rny written English.
Table of Contents
.. Dedication .................................................................................................................... n ... Abstract ........................................................................................................................ iu
...................................................................................................... Acknow ledgments iv
................... Table of Contents .... .................................................................. v ...
Table of Sample Codes .............................................................................. v u
List of Figures ......................................................................................... ix
...................... List of Tables ... ................................................................. xi ........................................................ .......................... I . Introduction .... 1
2 . Theory of Miscibility .............................................................. ............ 4 .............................................................................. Miscibility in Polymers 5
2.1.1. Ideal Solutions .............................................................................. 7
...................................................................... 2.1.2. Athermal Solutions 12
2.1.3. Regular Solutions ........................................................................ 9
...................................................................... 2.1.4. Lrregular Solutions 10
................................... . ................................ 2.1 5 . Polymer Solutions .... 1 1
Morphalogy of the Separated Phases and their Relationships with ......................................................................................... the Miscibility 16
........................................... . 2.2.1 Phase Transition on the Binodal 2 1
................................................ 2.2.2. Phase Transition on the Spinociai 22 ........................................................................ 2.2.3. Critical point 2 2
............................................................ Mechanisms of Phase Separation 24
2.3.1. Nucleation-Growth (NG) ............................................................ 26
..................................................... 2.3.2. Spinodal Decomposition (SD) 28
......................................... Morphology-Ph ysical Property Relationships 3 1
.............................................................................. 2.5. Fracture in Polymen 33
2.5.1. Deformation in Themplastic Polymers ....................... .. ......... 33
....................................................................... 2.5.2. Impact Fracture 3 4
2.5.3. Fracture Surface Morphology ...................................................... 35
.................................................................... 2.6. Techniques of Microscopy 36
.................................................................. . 2.6.1 Electon Microscopy 3 6
2.6.2. Scanning Probe Microscopy (SPM) ....................................... 3 6
2.6.3. Scanning Tunneling Microscopy (STM) ...................................... 37
.................................................................................................... 3 . Bac kground 40
.............................................................. 3.1. Monngraphs Used in this Study 40
...................................................................................... 3.2. Research Work 42
.................................................................................................. 4 . Experimental 44
........................................ 4.1. Materials
....................................................................................... 4.2. Sample Coding 46
.............................................................................................. 4.3. Equipment 47
.......................................................... 4.3.1. Microtome .................... ,, - 4 7
.................................... 4.3.2. Scanning Tunneling Microscope (STM) 47
................................... 4.3.3. Scanning Electron Microscope (SEM) 4 8
............................................................... 4.3.4. Conductive Coater 4 8
..................................................................... . 4.3 .5 Optical Microscope 48
4.3.6. Hotstage .................................................................................... 49
..........................*. . - 4.3.7. Differential Scanning Calorirneter (DSC) .... 49
............................................... ....................... 4.3.8. STM Tip Etcher .. 49
.......................................................................... 4.4. Experimental Procedure 5 0
4.4.1. Specimen Preparation ................................................................. 50
............................................................................. 4.4.2. Microtoming 5 0
................................................................................. 4.4.3. Fracturing 5 1
............................................................... 4.4.4. Solvent Treatrnent 5 2
.................................................................... 4.4.5. Thermal Treatment 5 2
4.4.6. DSC .......................................................................................... 53
................................................................... 4.4.7. Optical Microscopy 5 3
.................................................................... 4.4.8. Conductive Coating 53
4.4.9. SEM ......................... .. ........................................................ 5 4
4.4.10. STM ...................................................................................-.. 5 4
.................. 4.4.1 1 . Burleigh ISTM .... ...................................... 5 6
............................................................................. 4.4.1 2 . NanoScope 11 5 8
.......................................................... 4.4.1 3 . Particle Site Measurernent 60
5 . Results and Discussion .......................................................................... 62
Samples .................................................................................................. 62
Phase Contrast ........................................................................................ 62
.............................................................................. 5.2.1 . Microtorning 6 3
................... 5.2.2. Fracturing ........ ................................................ 63
............................................................. 5.2.3. Etching with Acetic Acid 64
..................................................................... 5.2.4. Solvent Relaxation 6 5
................................................................... 5.2.5. Thermal Relaxation 6 5
.................................... 5 . 2.6. Electron Irradiation ..- ............................ 66
......................................................................... 5.2.7. Natural Contrast 67
Optical Microscopy ................................................................................ 68
........................... ...................... Scanning Electron Microscopy : .. .. .. 6 9
............................................... 5.4.1 . Interpretation of the SEM images 71
................................................................. Scanning Probe Microscopy: -72
5.5.1. Burleigh Mucational STM ......................... .... .............................. 73
.................................................................... 5.5.2. NanoScope il STM 74
Morphology Studies ............................................................................. 74
Size Distribution Studies ......................................................................... 76 .................................................................................. 5.7.1 . SEM Data 76
................................................................................... 5.7.2. STM Data 79
........................................................................ Optical Property Studies 80
...................................................................................................... Conclusion 82
............................................................................................................ Outlook 85
References .................................... .. .......................................................... 86
Images and Graphs ...................................................................................... 9.1. Images ............................................................................................... ... 9.2. Grdphs ........................ .... .................................................. ... .................
Table of Sampte Codes
In order to easily refer to the samples with complicated compositions. a NO-digit number is assigned to every sample under investigation. The assigned numbers are defuied
as the sample code numbers. and their relations to the composition of the samples are given in the table below. x is the volume fraction of styrene in the copolymer and 4 is the volume fraction of the copolymer in the blend.
Tablc i. The codes representing different samples.
List of Figures
Figure 1 . A diagram showing the position and importance of morphologicd ........... studies in the chain of structure-properties relationships of polymer blends 4
Figure 2 . Lattice mcdel representing an ideal solution ............................................ 8
................................... Figure 3 . Phase diagram of a regular solution ............. ... 10
Figure 4 . Lattice m d e l representing a polymer solution ..................... ... .......... Il
Figure 5 . Dependence of the interaction parameter on volume fraction of
polymer solutions .......................... ,.. .............................................................. 16
Figure 6 . Phase diaprarn of a polymer mixture ...................................... ... ......... 17
Figure 7 . A typical diagram showing the free energy of mixing of a binary .................. mixture ds a funçtion of volume fractions. ...................................... ... 18
Figure 8 . Three regions of different stabiiity and their position relative to
........................................................................................... binodal and spinodal 20
Figure 9 . Phase diagram of a polyrner binary mixture with its binodal and spinadal ........................................................................................................... 2 4
............... Figure 10 . Mechanisms of phase separation in different regions of stability 25
. ............................... Figure 1 1 Phase separation by Nucleation-Growth mechanism 29
. ........................................... Figure 12 Phase separdtion by spinodal decomposition 31
. Figure 13 Cutting of the specirnens fiom the original sheets of samples ................... 50
Figure 14. Schematic diagram showing the mounting of samples in the microtome clamp. ..... . . .. . . .... . . . ... -. .. .. . . .... . ...- ..... . . . . . . ... .. . .. . ... . ,.. . -. . . .. .. ...... . ... . ... - 5 1
Figure 15. Making notches on the sarnple blocks before fracturing .................... . ...... 52
Figure 16. The schematic diagram of NanoScope iI Scanninp Probe Microscope. . . . .. . . . . . . .. . . . .. .. . . .. ... . . . . ..-m...-.....-.. .. . . . . . . . . . . . . . . . . . . . . . . . . . . .. . . . . . . . . . . . . 5 5
Figure 17. STM tip profiles prepared by ekctroetching at 6 volts. and at 12 volts- .........................-..............,..~*..*............**..........................*. ................. .. 57
Figure 18. The schematic diagram of the STM microscope of the NanoScope
I I instrument. ........................................................................................... 6 0
Figures A-1 to A-253 are discussed in "Results and Discussion " pari, and are illustmted at the end of the thesis.
List of Tables
Table i. Table of Sample Codes ............................................................................... k
Table 1. Densities of the investigated copolymers ........................... .. ............ 4 5
Table 2. Specifications of the original components of the plymer blends. Data ................................................................................................. from (ref. 2) 45
Table 3. Denotation of the sarnple code numbers and their relation to the . . .............................................................................................. compositions.. 46
Table 4. Dependence of the average size of the dispersed phases on composition of the blends. ............................................................................................. 7 8
TableS. Dependence of the average sizes of the dispened phases on composition of the blends. ...................................................................... 60
Introduction
The characterization of rnaterials and phenornena has always made a major contribution to the devetoprnent of science and technology. Technology in tum creates
new analyticai tools that are more precise and provide deeper insight into materials characteristics, and this interaction continues. This thesis deals with the application of the
recen tl y developed techniques of Scanning Probe Microscopy in elucidating morphological
rnicrcisnuctures in pdyrnenc matenais.
Polymers can be referred to as the rnaterials of the twentieth century. Their usefulness stem from the possibility of tailoring new materials with desired properties in view of the diversity of their properties which is a consequence of the ever growing
number of their varieties. Polyrner blends and composites are a major category arnong the
polymeric materials and can be made to have superior properties over their individuai
components.
There is a close relationship between the macroscopic properties of the polyrners
and heir microsccipic structures. In order to be able to design new polyrners with desired
properties, it is crucial to have a clear insight into the laws governine these relationships.
This work is a part of the pneral attempts that try to extend the scope of characterization
of polperic materials in order to help gain a better undentanding of their structure-
properties relationships.
Man y useful polymeric materials such as acrylonitrile-butadiene-styrene (AB S) and high impact polystyrene have been made by blending morphous polymcrs. Amorphous
polyrners do not undergo appreciable structure changes during their solidifcation process.
and therefore, desired phase structures can be tailored in their molten state and be frozen
in throug h rapid quenching. Properties such as compatibility of the components, surface
tension and viscosity. together with applied mechanical forces (such as shear rate of
rnixing in molten state). determine the final microphase structure of a solid blend.
In multi-phase solid polymer blends, morphology is one of the main contributors to
the various physical properties such as transparency, perrneability, elasticity and tensile
strength. Morphology describes the characteristics of the phase structure including the
domain sizes and shapes, and their s i x and spatial distribution. Morphology, together with
the interfacial forces beween the phases, determines the final properties of the blend.
Morphology is in turn determined by the intrinsic properties of the components and by the
conditions of the preparation of the blend. Therefore. a deeper investigation of
morphology will result in a better understanding of the laws governing the preparation of
polymeric blend materials.
In this thesis work, attention was focused on revealing the morphology of solid
polymer blends. The specific materials of interest for this work were the blends of homopolymer p d y ( nrerhyl ntethocrylate )( abbreviated as PMMA ), and the copolymer
poly( siyrerrc-CU-nwthyl methucrylate )( in short f o m as poly( St-CO-MMA ) ) in various
mole fractions. The copolymers used in this work were synthesited in the Deutsches
Krtrrststofl-Insrit~~t ( DKI ) in Darmstadt, Gemany, for research purposes, and the bled
samples were prepared at Central Research Institute of Chernistry (CRIC) in Hungary,
where detailed characterization of their mechanical and optical properties was also
perfinned. Morphoiogical studies usuig electron microscopy was initiated in Darmstadt.
Presen t stuciy was completed and complemented by investigations using scanning probe
microscopy at the University of Toronto, and the results are described in this thesis.
The work presented in this thesis is part of a collaborative research effort including
the Polymer Physics Group supervised by Dr. G. P. Hellmann at the Gennan Plastics
Institute ( DKI ) in Darmstadt, Germany; the Polyrner Rheology Group supervised by
Prof. B. Pukanszky at (CRIC) at the Hungarïan Academy of Science; and the Polymer
Material Science Group supervised by Prof. G. I. Vancso at the Chernistry Department at
the University of Toronto. The aim of this collaborative research has been to understand
the behavior of phase-separated polyrner blends.
The objective of this thesis work was to conduct a systematic investigation to
elucidate the morphologies of the sarnples by suitable techniques. Four series of
copolymer sarnpIes were used in this investigation. In each series, the sarnples had a constant copolymer composition with a certain ratio of St and MMA, and a whole range
3
of volume fractions of the blend components, Le., the copolymer and PMMA (10 different compositions for each çopolymer series).
Imaging techniques were chosen as the study tools, shce they provide direct views of the structure of the samples. The study covered utilization of the techniques of the
optical rnicroscopy. the scanning electron microscopy (SEM), and the scanning m e h g microscopy (STM). A description a d discussion of suitable methods of samples preparation and phase contrast for each of the above rnentioned techniques are also included in this work. Another part of the work involved quantitative analysis of the s ix distribution of the phase dornains and discussion of the differences in their average sites obtained from different techniques.
Optical micmscopy could only reveal the structural features of the sarnples with
highly irnmiscible components which corresponded to the high styrene containhg sarnples. Since the sizes of the morphological features were around the resolution of the technique,
Le. the wavelength of Iight. no quantitative assessrnent was possible. Scanning electron
microsccipy extended the irnaging power and yielded good resolution at hi& magnifications. but the harsh conditions of irnaging required by that technique damaged the samples and put a lirnit on the usefulness of the technique. However. good images could be taken from the samples with styrene contents of down to about 50%. Some quantitative analysis. es€. , the determination of the size distribution of the separateci minor
component in the mamx of the major component as a function of the volume fkaction could be done on the basis of the images from this technique. Fmaiiy, the scanning tunneling microscopy prduced excellent images with high resolution and extended the
imaging field to cuver silmost the whole range of compositions, and ailowed us to produce a quantitative analysis of the images. The difficulties here was found ro be in contrasting the phases, however, this was reasonably accomplished for the blends in question.
Theory of Miscibility
Morphology of pc&tner blends has its roou in the characteristics of ia components suc h as c hemical structure, molecular weight and its distribution; physical and thermcdynamic parameters such as the v o h e fractions and the interaction between the chains of its compiinents. Morphology is also a function of the preparation history of the samples including temperature and rate of mixing of the components, temperature and rate
of molding of the fluid mixture, temperature and duration of annealhg in the mold, and finally the means and rate of quenching. On the other hand. it is the morphology of the phases in the blends that dictate most of the optical and mechanical properties of the resulting solid plyrner.
Figure I. A d i a g m showing the position and importance O€
morphological siudies in Lhc c h . of stnicture-property relationships of the
plyrncr blcnds.
5
An investigation into both sides of the morphology relationships, as depicted in
Figure 1, has obvious importance. S uch an investigation, however, relies on the power and
reliability of the emptoyed techniques. in the following sections, after a discussion of the
general principles of miscibility of polymers and a brief review of the works of the other
researchers on the subject material, the techniques of elucidation of the morphology of the
separated phases are discussed in more details.
Thermoplastic polymers are usually used in their soiid States. This means that no appreciable changes take place in the relative positions of the polymer chahs with respect
to each other once they are formed. Consequently, the morphology and phase structure of
a solid polyrner bIenct is detennined in its molten state before and during its processing.
Although the prc~essing conditions and the kinetics of M g have crucial effects on the final morphology rif phases, it is the thermodynamic properties that determine to what
extent. if at d l , the components dissolve in each other and in what conditions and with what mechanism their phases separate. That is why the theory of miscibility and phase
separation finds some place in many of the papers that deals with the morphology of the
pdymer biends.
Miscibility in Polymers
Two molten polymers can only be mixed to fonn a stable homogeneous blend
when the free energy of mixing process is negativel. In other words. the criterion to obtain
a hcimogeneous mixture is:
where AC, , AHM. and AS, are the changes in the free energy, enthalpy and entropy of the
systern during the mixing prwess, respectively. By calculating the values of the two terms
6
on the right side of the equality sign, it is possible to predict the behavior of the
components in mixing'.
AH, is the heat of rnixing and is related to the interaction forces benveen different
types of mdecules in the mixture and can be calculated from the solubility parameters (6) of the components by using the Hildebrand equation2:
where Ys, is the vdume of the mixture and @, and Q, are volume fractions of the
components A and B. respectively. Equation (2) predicts a positive enthalpy of mixing for
liquids, or, in other words, the process of mixing is endothennic. This is the case for
almost al1 liquid mixtures with dissirnilar components. The larger the ciifference between
the two 6s. the more positive is AH,. Its value becomes zero when the components are made up of molecules with similar chernical structures. that is, when SA = &.
Applying equation (2) for polymer blends involves some approximations. The
approximations anse from the fact that the solubility parameters are obtained from the
heats of vaporiration of similar monomenc Liquids while polyrners are nonvolatile and
have large molecules.
AS, is the entropy of mixing which is always a positive quantity. therefore the
second term in equation (1) is negative, and consequently, the free energy of m b h g
becomes negative cinly when AH, equals to zero or its magnitude is small enough to be
«vercorne by the entropy term. This is the criterion for the rriiscibïiity of two Liquids: the
interaction between the twci dissirnilar molecules should be about the sarne as that for the
two similar molecules of the individual components. Here. we find the ongin of the d e
" 1 ikc dissol w s lik~?"'
For polymers. the entropy of rnixing is smaii, because the segments of their chains
are Iinkeû to each other and do not have the degree of fieedom to the extent that
monomeric molecules do. This rnakes the magnitude of the term -TASM very srnaii so that
in order to have a negative free energy of mking, the magnitude of LW, should be zero or
very small, which is the case for mixtures only with sirnilar components. Here is another mle: "Inmntpatibility in chemically dissimilar polymers is the rule and compatibility is the exceprioton". This is a quote from P. J. Roty on the miscibility of polymers3. However,
the incompatibility is relative and blends can (in certain circumstances of temperatures and interaction forces) have some degrees of miscibility.
A deeper look at the application of equation (1) to Liquids in general, results in
distinguishing four types of solutions':
Free energy of mixing for this type of solution is a function of only the entropy terni:
M , = O and AG, = -TM,
In this very rare case, the molecules of the components are similar in size and force field, and mix randomly without restriction. A lattice mode1 for an ideal solution is shown
in Figure 2, where the lattice sites are randomly occupied by the molecules of the
components. Here the entropy of mücing has its maximum value, which is referred to as
the "contbiriator-id enn-opy". Any deviations from ideality will decrease the magnitude of
entropy. which corresponds to a less negative free energy of mixïng. or. in other words,
will restrict the miscibility.
Figure 2. Latticc mode1 representing an ideal solution when: the black
circlcs ,arc ihc sites of the molecules of a monorneric solute. and the white circles
arc thc sitcs of the motecu1es of a solvent.
The cornbinatorial entropy of randomly muuig of two Liquids in ideal case is calculated in ternis of concentrations and is:
where k is the Boltzmann constant, N, and N2 are the number of molecules. and x, and x,
are the mole fractions of the cornponents in the mixture.
2.1.2. Athermal Solutions
ln the case of athennal solutions LW, = 0, but the entropy change is less than that of the irleal mixing due to the constraints that cause deviation from the random mixing. ui this case the deviation from the ideality arises from the differences in the size, shape and the preferred orientation of the molecules of the components with respect to each other. This results in even less miscibility.
2.1.3. Regular Sdutions
In these solutions the randornness of mixing is ideal, but there is some interaction
difference between the sirnilar and dissimilar species. Le.. when AH, # O. This is the case for most of the real solutions of s W molecdes, where the kinetic energies of the
molecules are enough to prevent ordenng, consequently there is no volume changes in these systerns. In this type of solution the entropy term is the same as that of the ideal case and the enthalpy terni is cakulated h m the interaction energies of the species according to the fdlowing equation:
where z is the cwrdinütion number around each species (see the lattice mode1 of Figure 2) and AE,, is the exchange energy of interaction which is calculated from the simple relationship bellow:
where E, is the interaction energy between the two dislike molecules, and ell and E2 are - the interaction energies between the two like molecules.
The free energy of mixing. therefore, is calculated by substituting equations (3) and (4) in equation ( 1 ) which results in:
Equation (6) gives the fiee energy of rnixing in terms of temperature and concentration. and is valid with two assumptions: fmst of aii that the molecuies of the components mix ideally. and secondly that the coordination number r, does not change with temperature and concentration. The phase diagram for this kuid of solution c m be
obtained by taking AG, = O and plotting the temperature versus mole fractions of one
cornponent, which results in a typical diagram as in Figure 3:
UCST
Figure 3. Pha..c diagnm of a regular solution. UCST is the Upper Critical
Soluiion Tcrnpcraiurc. above which the solution is homogentmus in al1
cornptwicions.
2.1.4. Irregular Solutions
Most of the solutions and mixtures of polymers are irregular solutions. For polymers. both AH and ASMare non-ideal, which rnake the calculation of h e energy and
M
hence the prediction of rnisci bili ty very complicated.
2.1 .S. Polymer Sulutions
Rault's law uses the mole fractions of the solvent in a dilute solution of small solute
species to express the colligative properties of the solution. This ideal-behavior iaw failed
to explain the behavior of poiymerss. The deviation of polymer solutions nom ideality anses from the nature of the sizes of their molecules and consequently a new theory was
needed.
Fl«ryls work on the thermodynamics of polyrner solutions coincided with the
works of M. L. Fiuggins6- and led to development of the equation of fÎee energy of muring
for polyrners. Fiory developed his theory of polymer solutions and blends by using an approach based on statistical therrnodynamics. For polyrner solutions, he proposed a Iattice mode1 that placed segments of the polymer chahs (rather than the whole molecule)
in the lattice sites. A typkal diagram of his mode1 is shown in Figure 4. Here the chah of
the polymer is randomly dispersed among the molecules of the solvent, and the ody
restriction for the segments to disperse randomly in the solvent is the comectivity of the
segments in form of a chain.
Figure 4. Laiiicc moclel rçpteseniùig a polymer solution. The black chcles
an: sites of the scgmcnts of a polymer chah, and the white circles are the sites of
the molcculcs of a solveni
Fiory found that it is the segment of a chah that conmbutes to the entropy of a
solution. In the equation of combinatorial entropy, he therefore replaced the mole fraction
ternis with the " site fractions ", that is
Xi = Ni
and - r ~ = f l 2
N1+N7 N, + xN2
where subscripts 1 and 2 denote the solvent and the polyrner, respectively. and x is the number of segments in the pdyrner chain. The new form of equation (3) becomes:
Since in ideal mixing there is no change in volume. that is AVM = O. the site
fractions can be converted to more practical quantities of volume fractions by ushg the
simple relations of:
where @ , is the volume fraction. V, is the volume of a single chah of the individual component. and V is the total volume of the mixaire. The final form of equation of combinatorial entropy in terms of volume fractions is obtained as:
FIory's lattice mode1 also provides a modification for the equation of the enthalpy
of mixing. By the same reasoning as above, equation (4) is converted to a function of site fractions as:
and to the volume fractions as:
By substituting the equations (8) and (10) in equation (1). the farnous k y -
Huggins equation of free energy of mixing for polymer solutions is obtained as:
or, alternatively, on a volume basis:
w here
The parameter "x" in above equations is known as the "Rory-Huggins
interaction parameter" and has a key role in the prediction of phase separation behavior in solutions and mixture of polymers. ln fact it is a dimensionless paramter that reflects the change in energy of a single molecule of solvent that penetrates into a polyrner. where
it obtains 2 neighbors and exchanps A&energy with each of them. in other words, kTx is the riifference in the energy d the solvent molecule in the solvent and in the polymer.
15
in the case of polyrner-polymer mixtures, the developrnent of a free energy
equation seems ici be very complicated However, by introducing the concept of interacting
"segments" of chains of pdymers, this derivation becomes easier in the zeroth order
approximation. In plymer blends, by ignoring the probable unoccupied sites as free
volume, the combinatoriat entropy is almost the same as that of solvent-polymer mixnires7. but the enthalpy term is modified by using an average "interacting segment"
volume Vs, instead of V,. which is the volume of one molecule of solvent, in equation (12):
The theory of Flory has successfully explained the behavior of solution and
mixtures of polyrners. however, some Limitations arise from the nature of his model:
Randcim choice of lattice sites is not truc if A&,? + 0 .
Entropy change of a polyrner chah under the effect of solvent is neglected.
Voids are excluded and only uniform density is assurneci.
Interactions farther than the nearest neighbor are ignored.
Dependence of x on temperature and M,distribution is underestimated.
Dependence of x on the concentrations is not considered.
The interaction parameter is a ünear function of concentration of the polymer
solution. Figure 5. illustrates such a dependency for a few combinations of solvents and
polyrners:
Figure 5. kpcndence of the interaction parameter on volume fraction of a:
plymcihylsiloxanc in benzenes: 6: polystyrene in methyl ethyl ketone9: and c: 9 plysiyrcne in ioluene .
2.2. Morphology of the Separated Phases and i ts Relationship to Miscibility
Even imrniscible polymers can be mixed to homogneous mixtures. dthough they
may not be stable. The large surface tension energies in interfaces of imrniscible Liquids can be »vercorne by applying appropriate energy of mixing. It is the amount of applied energy
and the mixing time that determines the final degree of homogenization. However,
homogeneity is a relative concept that depends on the scaie of masurement, and the t d y homclgeneous mixtures (which are in fact molecularly dispersed solutions), may never be obtained. After a çenain amount of rnixing, the process no longer hproves the
homogeneity. This limitation exists where prolonged rnixing can cause depdat ion of pcilyrner chains or chemicai changes occur as a result of heat buiid up.
Immediately after stopping the mixïng process, the heat starts to dissipate and the
system proceeds towards the thermodynamic equilibrium state, which favors the
separütion of phases for the less miscible Liquid mixtures. The extent of phase separation
depends on the temperature and the overalt composition of the mixture. These relationships are better understood by means of phase diagrams such as in Figure 6:
Figure 6. Phasc diagram of a polymer mixture. A homogeneous mixture
undcrgocs phase separaiion above the Lower Cntical Solution Temperature
(LCST) or hclow &c Upper critical Solution Temperature (ucsT)''.
Miscibility diagrams are made after examining the phase separation in the mixtures by means of several methods such as detemination of cloud-point temperatures and glass
transition temperature (Tg). Electron LWcroscopy has provrn that even the transparent
blends with a single tg obtained from both DSC and DMA techniques are phase separated in the sub-micron levels' '-
Thennoctynamic states of mixtures cm also be studied nom diagrams obtained
from free energy equations. By using the Rory-Huggins equation for polymer mixtures, A
G, is plotted versus the composition of one of the components at different and constant
temperatures. Phase diagrarns are derived from the coordinates of the inflection points on
these ~urves'*.~ as show in F i p 7, or alternatively, by taking denvatives of different
order from the free energy equation, as wili be discussed later.
Figure 7. A typical diagram showing the free energy of mixing of a binary
mixturc as a function of volume fraction of one of the components. and its
corrc~~ndençc io ihe phase diagnm.13
Phase diagrams indicate the circums*dnces under which certain phase States are thermodynarnically stable. As was shown in Figure 6, any conditions of composition and temperature that Lie in the imer side of the concave cuve in the lower diagram will result
in the separation of the mixture into two phases with certain compositions. Of course the
phase diagrams can only show tfie themodynamic equilibriums which may take quite a
long period of tirne to reach, and obviously changes take place only at temperatures above
the glas transition temperatures.
Depending on the specific conditions and the rate of quenching, this transition takes place via certain mechanisrns and results in certain types of phase-structure
morphology in the mixture. Since time is a major factor in the developrnent of
morphology, the practical way to study the mechanism of phase separation is to freeze the
phase structures in difierent stages of the transition through rapid quenching of the
mixture down to temperatures below their glass transition temperatures.
19
It is believtxl '' that the developmcnt of morphology passes through two stages: in
early stages of the phase separation it is the themodynarnic parameters of the mixture such as temperature, surface tension. and activation energy of the stable nuclei that dictates the type of the morphology of the separated phases. In the late stages of the phase
separation, it is the kinetics of phase growth that determine the concentration and / or the size of the phase domains. Therefore, in studying the phase structures of polyrner blends it is crucial to consider the history of preparation of the mixture. However, the early stage
has great importance due to its role in determinhg the type of the phase morphology.
J. W. Cahn" proposes a phase diagram c o n s i s ~ g of three regions: stable,
metastable, and unstable as shown in Figure 8. The boarder tines that separate different
regions have themcxiynarnic importance and are called binodal and spinodal cwves.
one phase
Metastabld /
1 Unstable \ / vetastable
1
Figure 8. Thrce regions of different stability of homogeneous polyrner
blends ,and thcir psiiions relative to bhodal and spinodal curves.
In the single phase region, the phase separation does not take place since the fke energy cif demixiri,q is positive. In the thermodynarnicaliy metastable region, the overail free energy of clemixing is negative, and the binodal curve represents the points where A
G , changes the sign. However, because of the activated nature of the phase separation in this region. the free energy of the system goes uphill to a Limited extent before decreasing. This accounts for a small psitive free energy in the demuing process in this region. Oo
the other hand, in the thennodynamicaiiy unstable region, the free energy of d e M g is negative everywhere. The two latter zones meet on the spinodal curve.
21
Bindal is in fact the curve of the cloud points where free energy of mixing changes the sign. and spinodal is the curve of the infiection points where the changes in
free energy of mixinp changes the sign. In other words. the binodal and the spinodal curves are the points at which the fust and the second denvatives of the free energy are
equal tci zero.
The binodal and the spinodal curves can be obtained by applying certain conditions
to the different derivatives of the equation of free enerw of mixing, e.g. the Flory-Huggins
equation. These were worked out long ago by J. W. ~ i b b s ' ~ , and are bnefly recalled here.
2.2.1. Phase Transition on the Binodai
The equation of the binodal curve for a binary mixture is obtained by taking the
fust order derivative of the equation of fiee energy of rnixing and equating the chernical potential of each cornpanent in each phase"
where i and j denote the components and A( is the number of molecules of the ?th
component. This equation can also be written in ternis of the mole fraction. Oi. instead of
NI. as was discussed earlier. The applied condition of chernical potential is
and Ap2 = A P ~
where the subscripts are the cornponents and the prime and unprime denote the different phases.
2.2.2. Phase Transition on the Spinodal
The equation of the spinodai c w e for a binary mixture is obtained from rk
second order derivative of the free energy of mkkg by taking it equal to zero as show
below ":
2.2.3. Criticai Point
The coordination of this point for a binary mixture is obtained by taking the third urder denvative of the free energy of mVUng equal to zero1'. This condition is an outcome of the fact that both the b inda l and spinodal cuves have a cornmon tangent at this point.
Phases are separated not up to pure components, but they proceed to a certain extent which is indicated in the phase d iapmsL6- Figure 9 shows rhernatically the
relationshi ps between the equilibrium compositions of the separated phases, which are connected by temperature tie-lines. The diagram was plotted for a hypothetical polymer mixture in terms of the c«ncentration (Q) of one of the cornponents, Say component A. The
phase separaticrn was examineci in a certain temperature ( T l ) and two different
compositions ($,) and (&). The temperature ciifferences between T, and the points on the
binodal and the spinodal curves are (AT) and (ATs), or the "quench depths" and the
"supercooled temperatures", respectively, and the distances of the original composition
from the equilibrium compositions are (A$) and (A@,), are the extent of the "super
saturation".
Figure 9. Phasc diagram of a polymer binary mixture with its b i n a
! d i d Iinc) and .spino<id (&hed linc) curvcs. At temperature Tl sample with
initial coinposition of @ and $1 decomposes inio phases with compositions of ($
'mi1 (&-44& ~spectively".
\
2.3. Mechanisms of Phase Separation
According to Cahni7. the separation of phases in different regions of the phase diagram proceeds through different mechanisms of initiation and growth. In the thermodynamically metastable region, the mechanism is the conventional nucleation and grow th (NG ), while in thennodynamicaüy unstable region the mechanism involves spinodal decomposition (SD). These mechanisrns lead to completely different phase structures, as are illustrated in Figure 10, which can result in different mechanical and pemeatian properties of polymers. Knowledge of the mechanisms of phase separation or "demixing" makes it possible to control the phase structures of the iiquid mixtures.
25
Consequently, desired structural morphologies of the solid mixtures can be obtained by rapid quenching of the mixtures at suitable points of thermodynarnic stability and kinetic
one phase
Figure 10. Mechanians of phase sepration in different regions of stabiity.
Merasrable region: phases separate as nucleation-growth ( NG ): Unsrable
r-egiort: undcrgws spinodal deçmposition ( SD ). A is the average wavelength d
the concentration fluctuauons leading to SD.
In thermodynamkaliy metastable regions, homogeneous solutions are stable to
minor perturbations, that is, unless sorne activation energy for phase separation is provided, a srilution can remain unchanged for a long period of hme. In a homogeneous
mixture. local aggregations and disintegrations of the like species (concentration
fluctuations) occur constantly, because the temperature is sufficient to overcome the
activation energies of the transitions. The formation of a nucleus in the NGdomain
involves two kinds of energy: one is spent in creating the surface energy, and the other is
obtained from intemal mass aggregation. The overall activation energy of fonning a
nucleus in solutions that do not have considerable interaction forces. is given by ~ibbs":
where y is the interfacial tension and S is the surface area of the nucleus of the formed
phase. By passing the activation energy barrier, d e w g cakes place spontaneously and
the system decreases its free energy by growing the nucleus. The number of the formed
nuclei as well as their concentrations ($9 are determined by the thermodynamic conditions
of the mixture e.g. the quench depth and the activation enerm. The immediae
surrounding of the nucleus is depleted of the species of the new phase to the extent that
the phase equilibrium permits (9,). The nucleus grows by taking excess species that have
amved as a result of the diffusion process. Growth is a kinetic process and the size of the
separated phase depends on the diffusion rate and the t h e spent. The size of a growing
droplet can be calculated from the ~stwald 's '~ ripening expression as:
where d,, is the drciplet diameter in buk themodynarnic equilibrium. y is the interfacial
tension. Xc is the equilibrium mole fraction of the depleting component in the matrix phase,
Vm is the molar volume of the droplet phase. and D is the diffusion coefficient of the
depleting component in the homogeneous blend matrix.
There are other nuclei growing at the sarne t h e as well, but the larger ones grow
faster at the expense of the srnaller ones. Droplets that are close to each other coalesce in
order to decrease their surface energy, so that large phase domains are formed and dispersed throughout the rnatrix. The shape of the dispersed phase is generally spherical in equilibrium conditions. however they may take the shapes of eiiipsoid or cyiinder
depending on their rhedogy in processine conditions. The distances of the droplets are
determined by t h e volume fractions of the compnents and in certain conditions of
viscosity and cornpcisition. the droplets connect to each other to rnake "percolations".
It can be concludeci that in the nucleation-growth rnechanism of phase separation
the concentration of components in the separating phases are detennined by the
therrndÿiiamic conditions of the mixture, and the dimensions of the droplets are
conaolled by kinetic parameters. mainly the diffusion coefficient and the length of time.
Figure 1 1 illustmtes a schematic diagram of the nucleation-growth mcchanism of
phase separdtiiin4. A h«m«geneous mixture of concentration $, with respect to the
component A undergoes dernixing by NG mechanism. The change in concentration and in
size of both the separated and the matrix phases are s h o w at four different times during
the separation process. The concentrations of the components in the growing phases are
constant throughout the growth, however. the matrix phase becornes depleted from the
species of the new phase as is represented by its concentration profile. The finai
concentrations of the matrix and the droplet phases are indicated as equilibrium
28
concentrations of and (Ob The vertical arrows indicate the downhill rnovement of the
concentration profile towards the depleted area as a result of diffusion, and the horizontal
a w w s show the size (d) of the formed droplets. The darkness of the gray s a l e also is a
measure of the concentration of the depleting component in the matrix phase.
In the thermorfynamically unstable region of the phase diagram, the hornogeneous mixture is not stable enough and minor perturbations result in the separation of the phases.
The rnechanism of separation in this region is spinodal decomposition, which is quite
different from the above discussed NG rnechanism. This mechanism bas k e n widely investigated by I. W. ~ a h n ' ~ ~ ' for noncrystalizing solutions of horganic glasses.
According to his theory, the concentration fluctuations occur as a result of thermal waves.
These fluctuations require some activation energy to bring about the phase separation. as was discussed for the NG mechanism. However, in the SD region of the phase diagram, there is no activation energy for phase separation, therefore the process is spontaneous
and separation commences instantaneously.
In this mechanism, the waves of concentration fluctuations interact and form a
highly interconnected network of concentration gradients at the early stages of the
separaticin process. As tirne elapses, the concentration gradients increase until the ultimate
equilibri um concentration is reached.
Figure 1 1. Phasc scparaiion by the nucleation-growth mechanism.-l The concentrations
of ihc compvncnis in ihc scparaied droplets are determined by the Lhermudynamic conditions
of thc rnixtum. hui thc domain sizes of the droplets depend on the kinetic parameters such as
the diffusion raie and ~ h c iime. The concentration ($4 and the size (r) of the droplet are
shown ai diffcwni iimcs (0. The heights of the bars and the darkness of the gray scale rcprexni the conccnuation of the component (2) in different phases. @a and qB are the
cquilihrium conccnlrriiions of the matrix and the droplet phases. rcspectively. The width of
bars ruid diarnctcrs of the circlcs represeni the size of the dispersed phase. Hem. the
wnccniraiion of ihe dropleis an: constant but ~heir sizes grow in rime.
Unlike in the NG mechanism. here there is no depleted concentration gap around the growing phases. The diffusion takes place in a continuous profile from the îess concentrated region to the more concentrated one. or in other words. the diffusion
coefllcient, D, is negative. This necessiîates a sign change for the diffusion coefficient in the border of the two regions, that is, on the spinodal curve.
The wavelenpth of the concentration fluctuations is determined by the
thermodynamic conditions of the mixture such as quench depth and overall composition.
During the phase separation, the wavelength of the fluctuations remains nearly constant,
and only the amplitude of waves changes in time. In other words, the dimensions of the
phases are fixed at the beginning, of the phase separation. but their composition change in time. This order of events is exactly opposite of what is observed in the NG mechanism. in NG mechanism, the composition of the growing phase is determined at the onset of the
formation of the nuclei. but its size grows in time.
Figure 12 iilustrates schernatidly the phase separation according to the SD
mechanism. The graphs illustrate the concentration of the component (2) in the separating phases at four successive times. The initial overall concentration is go. and the 6nal
equilibrium concentrations are 9. and Op. The wavelength of the fluctuations, k. is almost
constant, but the amplitude changes in tirne, which results in coarsening of the separated
phases. The clarkness of the gray shade is also an indication of the concentration. The
vertical arrows indicrite the direction of concentration growth and the horizontal arrows
indicate the direction of diffusion.
A cornparison of the rates of coarsening or ripening of the separated phases shows
rhat growih in the SD mechanism is much faster than that in NG mechanism. The higher
the temperature and the closer the fractions to 5050, the faster the coarsening2*. In some
blends the coarsening is extremely slow and the size of the separating droplets has a ünear dependency on the tirne, while for the interconnected r n o r p h ~ l o g ~ ~ ~ , the growth is very
fast and the sizes change exponentially in time.
Figure 12. Phase separalion by spinodal decomposition. The concentrations
(9) and sizcs (r) of the p k s are indiçaied in different times (1). The heights of
b'm ruid ihc &,ukncss of the gray shade represent the concenirations. Here. the
domain s i w ~ cor thc wavclcngths (k) of the separaied phases are constant but their
ronc~ritr-uriorrs Nrc-rcasc iti rime.
Morphology-Physical Property Relationships
Usually simple homopolymers are poor quality and thus have limited applications. However. numerous polymeric materials with useful properties have been produced by physical and/or chernical modification of the pure polyrners24. Homogeneous blends and randum copolymers often show synergism, and therefore, provide an extendeci range of properties. On the other hand. heterogeneous blends and composites have a broad diversity of properties that stem from the differences in morphology of the separated phases. This diversity allows one to tailor materials with superior properties. However. a dr3wbac.k is also asswiated with this process: in most cases, a weak adhesion of phases occur which correspond to poor mechanical properties. The mechanicd strength of the
32
blends can be imprwed by introducing certain kïnds of compatibilùer agents that act more
or less as surfactants25
Compatibilizers can be different types of copolymers made from the monomers of
the two components of the blend. instead of king a third component, the compatibilizer
can be one of the two components copolyrnerized to various compositions with the other
component: that is. the blend with formula P(A) / PA(1-,)B,. This blend necessarily will
exhibit a point of transition from the immisçible to the miscible state for any "x" value in
certain conditions of composition and temperature. This may occur in the immediate
composition vicinity of the pure components. This leads to the conclusion th& for the
blends of varyinp "x". it is possible to conduct the phase transitions in such a range of
temperatures so as to allow a stable liquid mixture to fom. A phase diagram made from
these transition points will help us to tailor the desired morphology for the blend.
The properties and the performance of polymer blends, and thus their practical
uses, are largely determined by the physical morphology in the micron and submicron
scaie. Morphology c m be controlled by alteration of the course of the mixingdemixing
process. Most of pilymers are immiscible with each other, and therefore, acquire only
certain morphologies that are controlled by the rheology parameters of the mixing. Some
other polyrners are semi-miscible, so that above (or below) certain critical temperatures
they show a mixibility gap in their phase diagram. Since demkhg of the homogeneous
mixtures results in finer and better ordered rnorphol~gies~~ than those obtained fiom
mechanical mixing, it is advantageous to induce some miscibility to the immiscible polymer
blends and then perform the demixing process.
Varicius types of morphology have k e n observed in polymer blends. One interesting type is the çcicontinuous morphology, or the socailed interpenetrating polyrner
networks (IPN). In this morphology. the domains of the component phases are not
separated. but make an interconnected network throughout the blend. This type has gained
interest because of its potentially good mechanical and permeation properties. Because of
their high interconnectivity. the toughness of theses materials is higher than that of the
simple dispersion blends. and it becornes possible to make thennoplastic materials with eIastic prriperties.
33
Blends with IPN morphology can be made fiom imrniscible polyrners by controlling the viscosity together with the composition of the mixturez6, or chemicaliy, by
successively crosslinking of the components in the preparation, or by SD decomposition of
the homogeneous mixtures as was discussed above". Another type of morphology is the dispersion in matrïx morphology which resuits in a certain mechanical behavior. This behavior is related to the site. size distribution. shape, orientations. and spatial dismbution
of the dispersed phase in the rnatrix. The possible shapes of the dispersed phase include
spheres, ovals. rods, or lamellae, depending on the composition, temperature, rniscibility, and the processing parameters. D. R. pau12' has a brief discussion on how the different
arrangements of phases can have a constructive or destructive effect on certain propedes of the blends.
2.5. Fracture in Polymers29
At room temperature polystyrene is a typical brirrle polymer. Its stress-strain curve
shows a very steep slope and only a few percent of elongation before break. Another type of behavior is shr~wn by hurd elastic or tough polyrners such as larnellar polypropylene
films. which have brith strong elastic property and good elongation at high stresses with
almost complete recovery on standing. PVC at room temperature is an example of a ducrik pnlymer. Such a polymer shows a steep dope in its stress-train cuve but it reaches
a maximum stress where it yields and with further stain undergoes unrecoverable
deformation by thinninp and necking known as the "cold drawing" or "plastic
deformation". A soft polymer is a polymer at temperatures just below its Tg, which does not sustain the stress and flows under applied pressures.
2.5.2. impact Fracture
Pol p e r s are viscrielastic materials. Their plastic de formation decreases with decreasing temperature and increasing load rate, or in other words, they becorne brittie. Resistance of a polyrner to impact forces sharply decreases with presence of stress
concentrators such as impurities, inclusions, and voids in the bulk, and flaws on the surface of the sample. In case of the test specirnens, these stress concentrators are induced artificially by applying a sharp notch on the surface of the samples.
When an impact is applied ont0 a specimen, the impact energy is absorbed and a strain is formed in the sample which in tum causes build up of stress in certain points. The
stresses result in defec~s in the fonn of "crazes" which, if not stable, will change to a rapidly propagating crack and breakdown of the sarnple. Stable crazes impart a hi&
impact resistance to the material, since they can absorb considerable amount of e n e r g that
otherwise would break the sample. For exarnple in the rubber-modified plastics iike ABS,
a large number of crazes is formed in the material as a result of fine rubber inclusions in brittle thermoplastic mauix. However, the crazes are stable at the rubber end due to
possibility of storing energy by elastic deformation.
Any molecular propeny or molecular process that assist the distribution and dissipation of mechanical energy and permit the attainment of a large deformation before
the inception of ripid propagating crack, will increase the impact strength of the materid. In this respect, properties such as relaxation. highness of the MW, partial orientation, and
unoccupied volume, increase the strength of the polyrner, and the strength of polyrner chains is much less important than the shear forces between the chains.
Isotropie samples show brittle behavior in cryogenic fracturing. in this case also the same sequence of events as in impact fracture take place; moreover, the rate of
quenching has influence on the onset temperature for brittle fracture. Increasing the
applied load causes scission of the most strained chains or the tie molecules. The released
radicals initiate a series of reaction which results in cleavage of more bonds in the vicinity of the original one. At this time a defect as a craze is created in the buk of the sample.
This kind of craze is also called an intrinsic craze, in contrast to the extrinsic craze which originates from the clefects and flaws at the surface of the sarnple.
Crazes impart certain properties such as stress whitening, high permeability, and toughening to the sample. A craze has a round disc shape, the plane of which is perpendicular to the direction of the stress. Unlike the crack, there is a continuity of
material within the craze which accounts for 50% of volume fraction. The fibrils are
created in the craze by defmnation and orientaticn of chahs rather than extension of the
fibrils. An average diameter of 100-200 nm has k e n detected for the craze fibrils. When
the sizes of the c r a z and the applied stress exceed certain values, the c rue is said to be
unsta ble and the crack propapates rapidly.
2.5.3. Fracture Surface Morphdogy
Fracture surface is created by a propagating crack. Cracks are created from
unstable crazes. A prcipagating crack causes a region of stress concentration around its tip,
which in turn. initiates the formation of the c rue at crack tip. It is the behavior of the tip
material that determines the morphology of the fracture surface. For example, if the tip
material fiows under the stress. then the crack is arrested and stops from propagating. This
necessitates reloading of the impact force which brings about a wavy pattern of features
on the fracture surface. Two cracks start to grow avoiding each other due to the stress in their proxirnity. then join forming a lip which is partially attached to the fracture surface.
Fracture surfaces are fonned as a result of both bond breakage and deformation of
the crack front craze. Deformation is a rate controlled process. this results in two
completely ciifferent patterns of features in fractures that propagate in two different
successive rates. In the cryogenic conditions the mobility of the chah is low, therefore the
features are small. In samples with structural elements such as extended chahs and
spherulites, the resistance of the material depends on the angle between the element and
the plane of the crack, therefore the crack propagates through certain paths in the bulk of
the sarnple which result in distinct features on the fiacture surface. in isotropie glassy
polymers the material separation is caused by disintegration of groups of entangled chahs
which result in a honeycomb structure with œlls of 100-1000 nm width; therefore no
microstructure can be concluded from these patterns. The ange between the local saesses
36
and the crack plane causes a curly pattern on the surface, and the direction of crack
propagation is determined by these stresses.
2.6. Techniques of Microscopy
The optical micrcwcopy, invented in the 16th century, provides a magnî€ying power
of up to 1000 time. It cm not resolve features of submicron size on the sample surface due
to the limitation from wavelength of the visible light (-0.5 pm).
2.6.1. Electron Microscopy
In 1927, Davidson and Germer discovered the diffraction property of e l e ~ t r o n . ~ ~
The wave length of the electron k is determined by its mornentum p accordinp to k=h/p.
where h is the Plank's constant (the proportionality constant in the correlation of the
energy of a particle with its frequency E=hv ). Therefore, very short waveiengths can be
obtained by accelerating the electrons in high voltage differences in a diffraction-limited
system of fwusing. With this technique a resolution at sub-angstrom level can be achieved
at least in theory The limitation arises from focusing techniques that use induction coils
and allow a beam wicith of not less than 100 -, especiaily in SEM that sans the reflected
or back scattered electrons. From the fust demonstration of the transmission electron
microscope (TEM) in 1932. it took a long time till now for particles of a few nanometer
size to be clearly rescilved (for example atom clusters of serniconductors31 in TEM micrographs). However. the technique requires a hi@ vacuum and c m not be used in situ
and for nondestructive studies of rnaterials.
2.6.2. Scanning Prube Microscopy (SPM)
An alternative to various types of the wave-source microscopies. is the probe
micro~copy~~. This technique is based on the interaction of a source point (the probe) with
the features on the surface. These interactions can have different nature such as attractive-
repulsive atomic forces, magnetic forces, electrostatics, or charge exchange, which are
used in designing different types of rnicroscopy, coilectively known as the scanning probe microscopy. By using piezo crystals, the tip surveys the surface of the sample in XY direction and the interaction forces are recorded and processed to produce an image of the
surface. Here, only the topilogy of the surface, but nothing beneath it, can be studied. The resolutiun of thrw t y p a of nlicroscopy depends on the -ce d m of the swfuce-tip int~'racfion and the t~&& of rhe tip.
2.6.3 Scanning Tunneling Micmscopy (STM)
Before the advent of the STM, another probe microscope with the name of "surfxe topographiner" was developed33 which used the sarne concept of the point
current scanning. In this design, the contrast was based on the high voltage field emission
rather than tunnelinp and therefore, the resolution was limited to the sharpness of the tip
which is typ id ly about 1000 -.
G. Binnig and H. Rohrer, the pioneers of the STM technique who also won the
Nobel price for their work. used the tunneling effect between the tip and the surface as a
basis for contrasting the distance in their probe rnicro~cope~~. if the rnetallic tip approaches a surface. at a distance of about 10 A electrons start to tunnel with a current in
the order of nanoamperes. Since the tunneling current changes exponentially with distance. the sensitivity of the technique f d s in the dimensions of the atoms, therefore the atomic rest~lution can be achieved.
During the course of development of the STM between 198 1 and 1986, Binnig and Rohrer overcarne the obstacle of keeping the tip-surface distance under control. The
problem originated rnainly fiom the themial and acoustic vibrations and resdted in considerable nuise. Also they found out that different tip fabrication procedures have
substantial effect on the shape of the tip surface, and it is quite possible that a single atom
sits on the apex of the tip. which could result in excellent tunneling images. An important
achie~ernent'~ by the atomic resolution STM was to solve the mystery of the atomic
structure on Si ( 1 1 1 ) surfixe which is known as the "7x7 reconstnicted surface of
38
silicone". (A 7x7 low energy electron diffraction pattern is observed on dean silicon surfaces. This pattern originates from an unusual structure formed by relaxation of surface atoms on the (1 1 1 ) orientation, which is completely different from its bulk structure).
The Tunneling of electron rneans that a narrow Stream of electrons can flow between the two ccmductors when they are brought to a distance of several angstroms but
with no physical cmntact. This phenornenon is explained by the wave nature of the electron motion in the metals. Electrons can not fiy out of the metal because of the large potential energy of vacuum. However, a tail of the electron wave enters the vacuum barrier and
decays rapidly. If aniither metal is brought close into the decaying region (3-10 A). a very
smali current (several nA) can tunnel. The bias voltage is the difference between the vacuum potential energies of the two metals and influences the steepness of the current-
distance exponential diagam. T u m e h g effect can be predicted and quantified by
quantum rnechani~s~~. Solving the Schrodinger equation in one dimension and for typical potential bamers of the metals, results in the following simptified equation for tumeling current:
where L is the distance of the tip from the surface in angstrorns. Since generdy the
sample surface is flat and the tip is sharp, there is a good probability that a single atom sits at the apex of the tip. thus al1 of the measured tunneling current will pass through this
point. By controllinp the magnitude of this current, the tip-surface distance can be controlled precisely in the angstrom range. Once the tunneling is reached, the tip can be made to survey on the surface of the sample which will result in varying tunneling cumnt depending on the roughness of the surface. Fuialiy by processing of this current, an image of the surface with atomic resolution is obtained.
The control of movement of the tip in angstrorn range is made possible by using the piezo electric materials suçh as quartz3? Chargcd atoms in quartz crystal have spccial arrangement. By applying a voltage across the crystal the mangement of the atoms
changes and the material contacts in one direction and expands in the other. The larger the
39
applied voltage, the more the change in dimensions of the crystal. For a Typical piezo
crystal one volt corresponds to a 150 A contract, therefon millivolts of voltage wîli cause
a sub angstrom displacement.
In practice, a piece of piezo material is cut in the form of a holîow cylinder. Four
electrodes are attached to four sectors of the cylinder and a fifth to its inner side. The cylinder is fixed on one side to a solid stand and to the tip on the other end. Applying
voltage to the peripheral and the inner electrodes results in movernent of the tip in XY and
Z direction, respectively. The pieu, voltages are controlled by the cornputer through the
scan parameters setting and by the feedback currents fkom tunneling. The controlled piezo
vottages cause the tip to scan over the surface and keep the tip at suitable distance in order
to obtain the desireci tunneling current.
E k c 1 and 3 --r X s a n
Elcct and 4 + Y scan
5 E k r 5 and 43.2.1 - Z scan
3. Background
The specific subject of this study was to explore the possibiiity of the use of STM for structural studies of polymer blends, and then to investigate the morphology within a
wide range of compositions of blends of two giassy polymenc materials: firstiy pure
PMMA and secondly random copolymers of poly(St-CO-MMA) with several chernical
compositions. Although the number of publications dealing with the specific subject of this
study is not large, a lot of research discusses difierent basic aspects of this work, such as theory, materials, rnethtds and results .
3.1. Monographs Used in this Study
Phase structure of plymers is a subject of discussion in rriany branches of polymer science and technology. Therefore, considerable research interest has been attracted to investigate the matter, and consequently, a wealth of literature about the subject has been
collected. In addition to numerous pubiished papers, dozens of monopphs can be found
that cover different aspects of the structure and properties.
The work of P. JO Fiory in 1953, "principles cf Pol~mer ~ h d m " ~ , is one of the classical textbooks in polymer science. In several chapters of his book, the author
sumrnarized his original papers where he established the theory of polymer solutions and
formulatal the thermcd ynamics of rnisci bility in Liquid polymer mixtures.
At the end of the IWO'S and in the early 1980's. several valuable monographs about polymer blends were published. 0. Olabisi and CO-authors provided a detailed theory of compatibility of polymers in their book "PoIIme . . . . r-Polvmer ~ l s c i b w ~ , when, after a comprehensive study of thermodynamics of phase separation in mixtures, thcy
focused on the properties and applications of miscible polymers. D. R. bu1 and S.
41
Newman published their two-volume book "Polvnt~r BI&"^^ , where, in addition to the thermcxlynamics of phase separation, the morphology, rheology and the optical properties
of pcilymer bleds are studied, and discussions on specific topics such as rubbery and thennoplastic b l e d s are also provided. Around the same tirne, ACS published
monographs on blends with the title "Polynter AI^'^. Another intereshng book was
translated from German with the title "An Atlas of Polyurer D- 1140 . Its authors, L. Engel and others. had collected typical images from surface examination of polymer
samples by scanning electron microscopy. A chapter of this book includes pictures of
fracture surfaces which were close to the ones produced in parts of this thesis work.
Since the mid 1981)'s, more books have been published which are specifically related to the thesis subject. D. R Paul with a second editor L. H. Sperling, edited 11 rconigoiicnt Polwrer ~urer&"" for Amencan ûiemical Society as one of the series on Advarrcrs irr Chmristry. In the papers collected in this volume, the main subject
was the c haracterization of polymer blends, and block copolymers, with an emphasis on the mechanical pmperties. A separate chapter is allocated to the subject of interpenetrating polymer networks. L. A. Utracki is the editor of several monographs on polymer blends,
most of whiçh have a rheology 1 processing focus. The one which is most relevant for this
study is the second volume of a two-volume book, "-t Topics in Pohmer ~cic~~tc~c~"'~~ublished in 1987. Others are "MuIt@ase Polmer ~[enc&'"~ published in
1989. "Polynin Allu~s urid le&"^ published in 1990, and "Tow-ehare Pol-ynrer
-"45 in published in 1 YO 1.
A book with quite a different topic from the above rnenaoned ones is "Pol~mer "" whose first author is D. Campbell. The book describes various
techniques fur the characterization of polymers. The chapter on optical and electron
microscopy were used in this work. The book of H. H. Kausch, "Polymer Fracrwe 1129 9
which provides a cmnprehensive theory of fracture rnechanics in polymers, is a usefui reference in studying structure-property relationship. FmaUy, the valuable book of A. E.
Woodward, "& uf Pol- M m ,147 , contains a good collection of images on
polyrner morphology which give the reader a better understanding of the subject and provide a reference for comparing one's results.
Research Work
The blends of glassy polymers PMMA, PS, and their copolymers have aiready ken studied frcim different aspects. The studies of their miscibility and its correlation to
the mrirpholopy of the separated phases have attracted considerable attentions. In this area, the work 40-46 on the blends with general composition of poly( AxB(l-x) ) / ply( A(l-y)By ) by the group ai DKI in Germany is especiaüy outstanding. In 1988 they publishedJR the results of their comprehensive study on the @ass transition temperatures of
these blends. according to which the copolyrner blends show a lowering deviation from additivity. In 1990. P. R. Kohl and others pubiished a papeF on miscibility of these polymers, where they found miscibility regions which were contrary to the Flory-Hueans
prediction. More details of phase diagrarns appeared in another pape32 by G. P. Helimann and others who studied the phase separation fiom cast fïim samples of certain compositions at different temperatures and times. It was found that the phase diapms, the morphology and the m d e of coarsening of the separated phases for the investigated cornpositirms are in agreement with Cahn's theory discussed in this thesis. D. Yu and others studieds" the theory of rniscibility and preparation of phase diagram from the cast
films in 199 1. At the same tirne. D. Braun and others investigated5' the morphology of the phases and gave a brief discussion of its correlation to the tensiie strength of the blends.
He referred tci the more detailed work on the tensile strength of thennoplastic blends and composites by L. A. Andradi and othersS2. who showed that the blends with separated phases are less strong than the homogeneous blends, and that the strength decreases with
the phase coarseness. ln another paper5' in 1992, D. Braun discussed the rniscibility
diagrarns of different copolymers with respect to their interaction parameten. and
concluded that the classical prediction of the miscibility is too simple to describe the
observations. Finally. in 1993. Andradi and ~ellmann- used the results from their past papers to study blend samples prepared by rnechanically rnixing and extrusion. However, their study was limited to a few copolyrner compositions with x=0.4, 0.5 and 0.6, and
even fewer samples for the morphology study. The present work tries to extend the scope of understanding the subject with a systernatical study of the morphology for al1 compositions of the copolyrner and the blends.
The group (if Pmfessor. B. Pukanszky in Hungary has developed theoretical models to interpret some of the expimental results obtained in DKI and in their own
43
laboratories on mechanical-property-morphology relationships. Some of the results of their experiments c m the mechanical properties of various blend samples have k e n used in this thesis work. which is in fact a part of the collaborative work beween the two institutes.
Experirnental
Materials
Materials used in this work were supplied by the Central Research Institute of
Chemistry at the Hungarian Academy of Science (CRIC). They were the remaining parts of sheets that were cut in dog-bone shapes for mechanical testing. The sheets were 1 mn
thick and were prepared from blends of different compositions. The original materials
were prepared in the Geman Plastics Institute @KI) and the blends were prepared" in a wide range of compositions. Densities of the copolymers are given in Table 1. More detailed specifications of the original polymers and copolymers were found in a m e n t
publication of L N. Andradi, some of which are given in Table 2.
The blends were made from two components: one was the homopolymer PMMA N8 and the other wüs a randorn copolyrner of ~ O I ~ ( S ~ ~ - C O - M M A ( ~ _ ~ ) ) . Four senes of
blends were prepared w i h f w r different "x" values. h c h series consisted of a whole ccimposition range (@) from O to 1 volume fractions in 0.1 volume fraction steps. The
btenris were homogenized in a Brabender rnixing charnber. The conditions of the mkhg
were 190 O C , 50 rpm. and 10 min. and the charge volume was 48 ml. The homogenized
blends were compression molded to 1 mm thick sheets and the dog-bone shape specimens
were cut from these sheets.
Table 1. Cmposi tion density of the investigated c ~ p o l ~ m e r s ~ ~
Pure PMMA* 1
2
3
4
Pure PS'
Copdymer composition I Density
St : MMA (9/cm3)
0 : 100 1.182
* Data csiirnatcd from the chain volumcs given in refaY.
Table 2. Spcificatic>ns of ihe original componenis of ihe polymer blends. Data Gum
ref.Y.
4.2. Sample Coding
For easy reference, the samples are named by two digit numbers: the first digit to
the left represenb the composition of the copolymr (it equals 10x where x is the volume frocrion of styrcJne in the copolymr); and the second digit to the left represents the composition of the blend (it equals 1w when @ is the volumefracrion of the copolymer in the blend). For example the code number 86 means that the sample is a blend made of 409 pure PMMA and 609 of the copolyrner that contains 808 of styrene and 20% of MMA monomers. Table 3. illustrates the correlation of the codes with the compositions.
Table 3. Nolalion of ihc siunple code numbers and their relation to the compositions: x
is ihc voluinc fraction of styrene in the copolymer and + is the volume fraction of the
copolymer in the blend.
4.3. Equipment
This thesis work mainly deais with the different techniques of irnaging of fkactured
or microtorned pdymer samples. In this chapter some specifications of the equiprnent used
are sumrnarized.
Microtoming was performed by an MT6000 uftrarnicrotome b r n Sorvaii
Instruments. The ultra mode was not used and the samples were microtorned by using
glass knives which were freshly cut by means of the 7800 knife ntaker from LKB Brornma.
4.3.2. Scanning Tunneling Micniscope (STM)
STM imaging of microtorned sarnples was possible by conductive coating their surfaces. Like for electron microscopy, a fine film of gold was deposited on the surface of
the flat microtomed surface by sputtering.
Two different STM instruments were used in this work. The early STM experiments were alcornplished by the instructional Scanning Tunneling Microscopy
(ISTM), systrni ARIS-2200 from Burleigh instruments Inc., Burleigh Park, Fishen, NY. The scan tips used in this study were made by electroetching of tungsten wires in alkaline electrolytes with a home-made electronic device. The software of the instrument that
controlled the imaging and performed the image processing was the True h g e ISTM Sof%we. The tunneling prwess was controlled by monitoring the tunneiing cumnt and
the piezo voltage by means of a two channel oscilloscope.
The later part of this thesis work involved irnaging the sarnples in the STM mode of NuttoScopc II Scunrting Probe Microscope from Digital instruments Inc., Santa
Barbara. CA. Figure Ih shows a schematic diagram of bis instrument. The software on
the instrument that controls the scanning operation, storing and processing the image data,
48
was the NunoSccope il Sofmwe version 55. The microscope is comprised of a solid metal base on top of which the sample is mounted. The scan &ad which includes the pieu, scanner and the tunneling tip, rests on the base at 3 contact points. (Figure 18)
4.3.3. Scanning Electrm Microscope (SEM)
Two SEM instruments located at the Department of Metallurgy of the University
of Toronto were ernployed. The one that was mostly used in this work was the Hitochi S- 520. The other that was used for imagine in the back-scattering mode and for x-ray mapping was Hituchi S-570. The latter was equipped with the Link AN 10000 analyzer.
4.3.4. Conductive Coater
Samples for SEM and STM were coated with conductive material by gold
sputtering fxilities of the electron microscope located in the Department of Metallurgy (Po laron ) and the Department of Botany (sputter coater E5000C-PS3 fiom PoIaron.Equipments Ltd.).
4.3.5. Optical Micruscupe
The instrument was the metallurgicul nzicroscope mode1 BHSM-3 13UI363U from
Olympus Optical Co. Ltd. equipped with the Nomarski pnsms to work in the phase interference mode. Dunng high temperature work. special long working-distance
objectives were utitized.
Hot Stage
This device. 1i M~trker- FP 82 HT with Mettler FP 80HT central processor, was a part of the optical microscope used for studying morphology changes with temperature. The hot stage was equipped with a speciai ceii char in addition to providing the suitable optics for high magnifications, could also control the atmosphere at the surface of the
sample.
4.3.7. Differential Scanning Caldmeter (DSC)
The DSC used was the Perkin-Elmer 7 Series Thermul Analysis System and was
employed in measuring the glass transition temperatures of the sarnpies.
4.3.8. S T M Tip Etcher
This device was made in the workshop of the Department of Chernistry and consisted of a clip to hold the tip, a micrometer to finely control the height of the tip in the
soluti<in. a ring of p l d wire to serve as the cathode around the tip, a power supply, a
potentiometer to provide the desired voltage up to 12 volts, and an electronic unit to
prnvide irnmediate cutting of the current in the event of sudden increase in the resistance of the etching circuit
4.4.1. Specimen Preparation
PoIymer samples were cut to blocks of 2x3 mm and 3x5 mm from their original pieces in the machine shop of the Department. The thickness of ail of the sarnples was about 1 mm (Figure 13).
Piece of sample
/ Sample 4 1/01 2 mm blocks
d Top side
Figure 13. The original sarnples in the form of pieces of sheets which
rcmriincd h m ihc dog-bonc specirnen cuiting. were cut hto 2x3 mm blocks.
4.4.2. Microtoming
Two types of samples were obtained by microtoming. These included blocks with smooth surfaces, which were the "left overs" of the rnicrotoming process, and slices, obtained durinp microtoming, with a thickness of about 200-500 nm. In a few early experiments, the samples were microtomed on the top side of the blocks as shown in
Figure 13. tn the later part of the work, i.e. in the STM experiments, they were cut on the side face of the blwks. Generally microtoming was done at room temperature. Cryo- rnicrotorning probably could eliminate possible deforrnations resulting from ductile cutting.
51
Therefore. attempts were made to cool the sample and the edge of the knife by spraying
sorne liquid nitrogen on the sample immediately before the cutting.
In rnicrotoming. the blocks of samples were held directly between the jaws of the
instrument's clamp in early experirnents. which was indeed a diffïcult practice. Later, a special sarnple holder was designed (Figure 14) to obtain very flat and level surfaces. The polymer block was hard-glued on top of the sample stub, which in tum was secured in the
metal block as in Figure 14.
i r e 4 . Schcmaiic diagram of mouniing the sample blocks in the
microtome clamp.
The g las knives for microtoming were cut from commercial g l a s rulers. The
speed of cuttinp was chosen to be about 5 mm / sec for the specimens in the fonn of blocks and 0.5 mm / sec fur the specimens in the form of slices.
4.4.3. Fracturing
This technique was employed for the samples for which smooth microtomeci
surfaces dici ncit reveal any phase structure of the sarnples. Fractured surfaces were
prepared by notc hing the sample block at the middle of its top surface by rneans of a blade or by mi~mtoming with the corner of the @ass knife, followed by applying a sudden
impact at the back of the block (Figure 15). Early fractures were prepared at room
temperature. Later, in order to have truly brittle fractures, a freeze fracturing technique
52
was adupted. The procedure was the same as that for the room temperanire fractuMg, but
it was performed in liquid niirogen. In the latter case, many samples did not break on the
notched lines. The fractured surfaces codd only be studied by SEM, since optical
microscopes do n«t have enough depth of field at high mag~~cations and thus are not suitable for rough surfaces.
figure 15. Norches made on the sarnple blocks before fracturing.
4.4.4. Solven t Treat men t
In order to enhance the phase contrast at the surface of the samples, one method is to treat them seiectively with suitable chemicalss6. Acetic acid was used as the etching
agent that removes one of the phases, i.e. PMMA, from the surface. The sarnples were
treateci with this reagent for a few minutes. Moisture and methanol were employed to
bring about the phase enhancement by a process known as the "solvent relaxotionNS6 (see also the section "revealing the phase structure"). Moisture was applied by spraying a few
droplets of water onto the surface, and methanol was brought into contact with the
samples overnight.
4.4.5. Thermal Treatment
Heat treatment was employed on one of the samples to investigate the appiicability of the phase enhancernent process known as the "themtaf for the samples
under study (see also the section "revealing the phase structure"). Sarnple 82 was d e d
in the hot-stage of the optical microscope and under nitrogen atmosphere. The sample was
heated at a rate of I O OC/ min up to 112 OC, kept at this temperature for about 6 hours, then cooled at a rate of 0.2 OC/min for two hours, and then lefi to cool down and reach the
rocim ternperature which was equivalent to a cooiing rate of IO "Umin.
4.4.6. DSC
This instrument was used to obtain the glas transition temperature of the samples in an attempt to evaluate the possibility of contrasting the surface features through the
thermal relaxation prwess. Tg of samples 30 and 810 was detecmined by DSC experirnents. The mass of these samples was 12.5 mg and 18.2 mg, respectively. The calibraticin of the instrument was perforrned at two points with the standard samples of
indium (mp =156.60 OC) and decane (mp =29.40 OC). The heat flow to the samples was recordeci while the temperature was increased at a rate of 10 OUmin between 75 OC and 140 OC. Both the first and the second nins were recorded for each sample.
4.4.7. Optical Micrcsmpy
For viewing the flat microtomed surfaces of the sarnple blocks, the reflection mode
of the micr«scope was employed. For obtaining better resolution specially in the z
direction, the Nomarski prism was employed, and viewing was performed in the differential phase interference contrasting mode. In this mode. blue background color gave
the best resolution. The slices were viewed by both the bnght field and the interference coneast mode. In cases when the surface was not very flat, and especiaily for taking the
54
photographs. the opening of the aperture was set to minimum. The typical exposure timc in taking the photographs was about 30 seconds.
Samples were gold coated before the imaging in SEM or S m . The microtomecl
samples were glued on the aluminum SEM stubs by conductive glue (for blocks) or by
double-sided scotch tape (for slices) before gold sputîering. The sputtering chamber was
evacuated down to 10-2 millibar vacuum and argon leakage was allowed to the extent that
produced about 20 mA of current. Under these conditions, the coating was performed for
60 seconds. which corresponds to a thickness of about 4 nm of gold, according to the
instrument's manuai. In one case, when the use the x-ray mode of the electron microscope
was useci, carhm coüting was applied in order to allow the electrons to penetrate into the
sarnple.
4.4.9. SEM
The SEM technique was employai for imagine the fracture surfaces of the samples
or irradiating and imaging the thin slices of the samples. The samples were gold-coated
before imaging. Fractured samples. after king mounted on the aluminum stubs and king coated with gold to a thickness of about 40 A, were irnaged by the Hitachi S-520 SEM instrument. Imaging by the SEM was tedious because many of the samples decomposed
under the influence of the high voltage electron beams. and therefore, imaging required
separate optirnization for each sample. High styrene containine samples were scanned at
magnifications of X 10000-X50000 with typical settings as acceleration voltage =20 kV, electron beam current =120 Pm, working distance =10 mm, and bias =5 divisions. Softer
samples i.e. those with higher PMMA content, could only be scanned at magnifications Iess than X 10000, and only with electron acceleration of 5 kV. Those criteria correspond
to low resoluticin imaging, and therefore put a litnit to usefulness of the SEM technique
for such kinds of polyrnen. Neverthcless, m y good images were taken from the
fractured surfaces. In the case of irnaging the slïce samples, decomposition of PMMA
55
phase was intendecl. Therefore, the samples were irradiateci at a suitable voltage for an optimum penod of time between 5 to 30 minutes before photographing the images. In the single case of X-rdy mapping, oxygen was chosen as the indicator elernent
4.4.10. STM
The discvvery of STM by G. Binnig and H. ~ohre?' from lBM in 1982 opened a new window to the world of surface science, and especialiy to the study of surface
phenornena in the atornic scale. Since then, a considerable amount of re~earch)~ has been devoted tri the thetiry and application of this new technique. However, most of the
attention was paid to its applications in the atomic sale studies of metals or
semiconductors. Because of the lack of electrical conductivity in most polyrners, this
technique has not k e n used for this type of material. Nevertheless, polymers can be
coated with conductive matenal for the smdy of phase structures in sub micron scales,
which is far above the grain site of the coating material. The rnild operatine conditions and
the high resolution of STM make it a promising alternative for the electron microscopy for
studying delicate and sensitive samples such as those of our polymer blends. The
experimentx were started without relying on the preceding works, and therefore there are not many references cited in this section.
Figure 16 shows a schematic diagram of this instrument. The direction of the flow
of data and also the c»ntrd commands to the different parts of the instrument is s h o w by the arrciws in the diagram.
Computer Workstation Electronic Control Unit Microscope
Figure 16. A schcmtic diagram of the NanoScope II scannuig pobe
miçroscopc. Arrows indicaie the d i r e c h of the flow of uiformation-
The tunneling current is arnplified and digitized in the electronic control unit of the instrument. The çcimputer workstation controls the scanning parameters, records m e h g
current (or the tip height) as a function of the tip position on the sample surface, processes the data. and displays in real time an image that represenu the features on the surface of the sample. There are two modes of operation for the scanning process: the current mode and the height mode.
In the current mode. which is suitable for the scan ranges in the atomic level, the
tip is kept at a constant height, 2, from the surface, while it rasters in the XY direction.
Features of the surface with different abilities to tunnel, that is, those with different
eiectron cloud density at Fermi level, give different tunnelhg currents as the tip rnoves in XY directicins and at a constant 2. The digitized current is stored as data points in the
computer and is displayed as a function of the position of the tip in form of an image. The variation in the current is demonsnated in colors or gray tones which are depicted as a scale bar beside the image on the screen.
In the height mode, which is suitable for scanning in large areas for topographie
studies. the tunnetinp current is kept constant while the tip moves in al1 X, Y, and Z
directicins on the surface. Here a voltage is applied to the z component of the piem drive to make the tip follr>w the features of the surface. This voltage is digîtized in the electronic control unit, and is stored as the data points in the computer. This data is displaycd as a function of the tip position to construct the image. The variation in Z piezo voltage is
57
shown as different colors or gray tones in the image. The gray tone of the picture is a
rneasure of the topogrdphic Z dimension or height of the features on the surface.
4.4. 11. Burleigh ISTM
The STM technique had not been employed in the study of morphology in polyrner
blends before. to the best of the author's knowledge (except in one case in studying of the
polyethylene lamella5n), therefore, in this work, there was no procedure for conducting the
imaging process. other than the general instructions given by the supplier in the rnanual of
the instrument.
In case of the Burleigh's instrument (ISTM), the tips were made by electrochemicd
etching tif a 0.1 25" tungsten wires9. For the experirnents with the Burleigh ISTM, the tips
were prepared as described in this reference. The method involved a simple
electropolishing of the wire. As the anode, the wire was inserted a few mm hto a 2N
alkaline electrd yte and was etched by applying 12 volts of DC current. The wire pdually necked just below the interface of the liquid and finally was cut as a result of the weight of
the less etched lower part of the wire. Desired shapes of the tip profile can be obtained by prograrririiing of the vuitage with tirne. (Figure 17).
Since the study aimed at the topographie images, the operation mode of the
instrument was chosen to be the height mode. i.e., the constant current. Scan size was
selected to be Y 0 0 0 0 A x VOOOO A. or. 9 pm x 9 pm, which was also the sîze of the SEM images at a magnification of X 10000. This scan size was chosen in order to be able to
compare the images obtained from two technique of STM and SEM.
The settings of the operation parameters of the instrument was highly dependent
on the conditions of the individual samples. e.g.. roughness of the sample surface and effectiveness o r quality of the conductive coating. A typicai setting of the parameters for
scanning of an average flat sample was as following: bias voltage =+1.00 volt, tunneling
current =#.O PA, delay time =2.000 mec. The servo loop control nubs were set as the
following: gain (proportionai) at the maximum and just below which the tip started to
58
oscillate with respect to the surface, time constant (integrai) at the minimum, and the fîïter at slightly above the minimum.
Figure 17. STM tip profiles prepared
at a: 6 volts, and b: at 12 volts.
The rate of scanning had a drastic effect on the quality of the images. It was found that optimum images result from low speed scanninp, typically 3 minutes or more per scan. The scan rate was controiied by setting the deiay t h e on the parameters menu on
the screen. The delay time is the time elapsed between the sampling of two data points
when the tip scans in the x direction (max. 256 data points). Negative bias voltages ais0
gave images. but the resolution was not as good as with the positive bias.
Negative bias voltages worked better with the rough surfaces, where, with positive
bias voltages. the tip crashed ont0 the surface. Contrary to hard samples, which give better
images when scanning for long periods of tirne, these sarnples gave the best results in the
first few sçans. and repetitive scanning wore out and damaged the surface (as is e v i d e n d
by the disappearance cif the features of the image) and frequent adjustment of the settings was necessary.
The piezo voltage in the z direction and the tunneling current were monitored by means of an oscilloscope, and the images were recorded when the sine waves on the oscilloscope were smooth and stable. The images were recorded in the cornputer as raw
59
data and withciut any image processing. The pictures shown in this thesis were obtained by
taking the photographs of the cornputer screen displayhg the images after some image processing. For this purpose the raw images were corrected for their plane tilts, the
magnitude of which was suggested by the software. The z range of the raw images was
too large. therefore. the images were duil. In order to make the images more clear, they
were pmcessed to have a z contrast range of equal to the standard deviation of the z values which was also calculated and suggested by the software.
This instrument was used a k r completing the studies by the Burleigh ISTM. It has
the advantage of more computerized controiiing of the scanning parameters and producing Iarger screen output in sense of the number of pixels. It has many fnendly on-screen features to control the scanning process and powerful software that aiiows manipulation of
stored data. The images in this instrument are much sharper than those obtained by the
ISTM, since, it displays images of 400x400 data points in contrast to the 256x256 data
points of the ISTM images. The cornmercidiy available Pt-Ir tips used for this setup were
found advantageous in saving time and achieving more constancy in tip quality. These convenient features made i t more attractive to use. Nevertheless, the information obtained from this instrument was not really very much more than was obtained fkom the ISTM.
The same samples thrit were used for the Burleigh (and not new samples) were used to image in NanoScope II. Here again the images were recorded as raw data, the o d y difference k i n g that the contrasting was done automatically at the moment of scanning.
The scanninp was performed in the height mode by using commercial tips made from the wires of platinum-iridium alloy with a diameter of 0.01 inches. After having
experience with the ISTM. operating the NanoScope 11 instrument was not as difficui~ Concerning the scan size, the "D" head with a maximum scan area of about 12 Vm x 12 p rn was chosen, since it gives image sizes comparable to those from the ISTM and SEM instruments used before. The tips were commercial and some of the instrument setthgs
(such as the voltage and the tunnehg current) were adopted fiom previous work. As
mentirineci earlier; the samples used in this instrument were those previously used in the
60
ISTM for better comparison of the images produced by the two instruments. They were
detached from the SEM stubs and were mounted on a metal foil by means of a conductive
glue. In this case. a rnwh better view of the tip position on the surface was possible by
utilizing a couple of binocular magnifiers.
Figure 18 shows a schematic diagram of the STM microscope. The tip is fixed on
the piezo driver. A servo motor causes the head assembly to tilt to the front and
consequendy to iower the tip to a certain distance that is controlled by the computer after activating the "engage" command, Once engaged, it is the voltage applied to the piezo
crystals that rnoves the tip in the x, y. and z directions or, in other words, scans the tip
over the sample surface.
- Piezo Driver Tip Holder
Coupling
Figurc 18. Thc schcmatic diagram of the STM head assembiy of the
NanoScripc I I insirumcnt.
Once the tip has been lowercd rnanually within close the proxhity to the surface
for less than 1 0 0 Pm, no more handling is necessary and the system is compleely
conirolled by the computer. A large menu of setting parameters. together with the
numerous comrnand options, cornputer-make the system very flexible and versatile for
different types of sümpk su r f e s . A few typical setting parameters optimized and applieâ
in the scanning operation of this instrument arc as following: Z scan range = 100 to 500
61
nm, XY = Y 0 0 0 x V(H)O nrn and 4500 x 4500 nm, no. of samples points per scan 400 x
400. scan rate = X Hz. set point current = 1.9 nA, bias voltage = 550 mV. gains = 26, and planefit enabled. Here also the images were recorded as raw pictures, and only a limited
number of image analysis operations were applied befare taking the photographs.
4.4.13. Particle Size Measurement
The pictures from the SEM experirnents were prepared as picture slides and were projected on the screen of a profile projector with magnification of x10. The dimensions of
the features were measured by a d e r with 1 mm divisions on the screen, and then converted into the units of nm. The 3 pm scale bar on the SEM images. was 90 mm on the
projector screen, therefore. for the images with magnification of ~10000, every rrim on the
screen corresponded to a distance of 33 nm on the surface of the sarnples. The accuracy of measurernent on the screen was fO.5 mm, which is equivalent to f 17 nrn and f9 nm, for
the SEM images with the magnifications of xlOûûû and ~20000, respectively. The particles with ellipsoidal shapes, which were not more than 10% of the total number of the particles. were approximated by circles and their diagonal diameters were used in the size distribution studies. Histograms of size distributions were plotted using "Cricket Graph" software on the Macintosh computer.
The pictures from the NanoScope iI STM were stored electronically in computer disks and were retrieved for funher studies including size measurcments. The size of the features was rneüsured usinp the instrument's software. Here. the accuracy of the
measurement was about -0 nm for the scan sizes of 9000x9000 nm, and +10 nm for the scan sizes of 45(M)x450() nm.
Resul ts and Discussion
The main goal of this thesis work was to explore suitable ways of e luc ida~g the
phase morphologies of the sarnples under investigation and to discuss the observed
morphologies in conjunction with the physical properties of the sarnples. Therefore, a
major part of the thesis includes the expianation of theses attempts d their results, and a discussion of the observations with respect to the existing knowledge about the subject
rnaterials.
5.1 Samples
Generally sampling was reproducible and the morphology was found to be the
same for sections taken from any spot of the buk of the sample. However, in some of the
samples, such as 88 and 89, side cross sections revealed some inhomogeneous layers. in these regiuns. the size of the phase domains were found to be about twice the size as in the other parts of the sample. This indicates that some parts of the samples did not rnix
well enwg h, or more probabl y, that they experienced different quenching rates. These
inhcimcigenities may impose some systematic error to measurernents and quantitative
assessrnent of murphology. However. these regions did not make up more than about 10% of the surface of the sample. and therefore were considered a systematic error and were
excluded from the quantitative analysis.
Phase Contrast
As mentioned earlier, if fiactured or microtorned surfaces do not have enough
features that can be studied dhctly, some method of nveaiing the phase structure of the
bulk becomes necessary. In this work. in addition to direct study of the fracture surfaces,
63
several methods were u . d to try to contrast between the phases of the components of the blend.
The plaïs knives used in the microtoming were very sensitive to the touch and becarne blunt after a few strokes of cutring. This resulted in creation of striations on the surface of the microtorned biocks. In order to distinguish this effect from the morph<il~gical feütures sought in the samples. a sampk of pure copolymer 80:20 (code
number 810) was microtomed and imaged as a reference (Figure A-1). The thin siiœs from the microtriming also suffered from this M e effect as they deformed. distorted. and shrank at certain points (Figures A- 1 15 and A-1 12).
Ideal rnicr«toming creates a very smooth surface with no further deformations on the partition faces. This can be achieved to some extent by cryogenic fracturing with very
sharp and clelicate diamond knives. Unfortunately neither was available for this work. and
therefore sorne restrictions were imposed on the experimenu. The fieeze microtoming as described in the procedure. did not give very smwth surfaces; rather, they looked idce fiatiy fractured surfaces (Figures A-45, A-5 1, A-52, A-53, and A-109).
5.2.2. Fract uring
This method was employed where the smooth microtorned surfaces did not reveal the phase structure of the samples. Fracture propagates through cracks that are created at the weak points of the buik of a polymeric material. These points are in most cases
concentrated at the interface of different phases. Therefore, the resulting surfaces carry the
information about the morpholcigy of the phases. If the crack by-passes the interface and proceeds through the phase, then there are not be enough details and it becornes necessary tri reveal the structure by one of the methods discussed below.
64
The sarnples investigated in this work showed both of the above mention& crack-
propagation rnechanisrns. The styrene-rich samples i.e. sarnples 87, 88, 89, 58 and 59,
showed discrete particles of PMMA dispersed in the copolymer matrix, as is evidenced by
the relative abundance of their comprising components. m e r s had either no indication of
such a kind of morphology. or provided images that were dificult to interprct. Numerous
micrographs of the samples have been taken and the results will be discussod in the SEM section.
Room temperature fracturing even below the glas transition temperature
resembles the behavior of ducale fracture to some extent, Freeze-fraçniring which is
carried «ut in liquid niaogen, is associateci with brittle fracture (compare Figures A-1 1 and
A- 12 with Figure A- 1 0 ) . Ductile fracture was induced by performing the fracture in
cryogenic conditions. This enhanced the phase boundaries of the dispersed particies in
some samples (compare Figures A-69 and A-84 with Figure A-1 1 1), while, in the others,
maskeri even the Iimited information obtained from the ductile fracture in room
temperature. These ciifferences wili be discussed in the SEM section.
5.2.3. Etching with Acetic Acid
Acetic acid etches PMMA much faster than polystyrene56. Therefore, it potentially
could reveal the phase structure by removing the PMMA phase and leaving the other.
Several samples were treated with a 10% solution of this acid for pends of 15 seconds to
6 minutes. The resulting surfaces showed features that couldn't be assiped to any of the
phases prribably because of partly etching of the copolymer as weU (Figures A-6, A-8 and
A-Y ). Since the copolymer itself contains MMA elernents, the etching approach would not
be fmitful for the samples with low styrene contents, therefore this approach was also
abandoned.
5.2.4. Solven t Relaxation
A suitable solvent can enhance the phase contrast between the phases on the
surface of a smoothly microtomed sample bl0cks6. When the sample is brought into contact with the solvent. at frrst it sweUs due to absorption of the solvent. This effect
lowers the Tg which is an indication of the case with which the polymer chah segments
move with respect tci each other. Consequently, the c h a h find a better chance for relaxation cif their strains and relief their frozen stresses, which corresponds to the contraction of the polyrner. The contraction of one of the phases results in a phase
contrast at the surface. This process creates new stresses at the interface of the phases in the b u k of the polymer blend, which creates cracks in the sample.
A microtomeci block of the sample 89 was kept in methanol for a pend of two days. This did not enhance the features to a great extent except that the microtome traces
vanished and large cracks were created (Figure A-2). Ethanol also was tried for a few
hours cif contact time, but had no discernible influence on the sample 89. Droplets of moisture on a freshly microtomed surface created a swollen circle with gradient phase
contrast across the radius of the circle. This approach was given up due to ambiguity in
contrulling the extent of the swelling by moisture.
5.2.5. Thermal Relaxation
This methd takes the advantage of the ciifferences between the Tg's of the
components of a blend. According to this rnethod, the sarnple is heated up to a temperature that is well above the Tg of one of the components and just below (but close
to the Tg of the other component). This leads to the sarne kind of phase contrast and assrxiated problems as was discussed in the solvent relaxation section. Here, the
component with the Iower Tg contracts as a result of relaxing its fkozen stresses. This
methocl seerns to be effective for the blends of polymers whose Tg's are far enough apart. Since at the time of the experiments the Tg's of the original components of our samples were not known. attempts were made to masure them by diffenntiai scanning calorimetry (DSC).
66
The results of the DSC expcrimnts showed that the Tg of the pure PMMA (sample 30) and that of the pure 80:20 copoiymtr (sarnple 810) were 1 lS°C and 103OC,
respectively (Figures A-252 and A-253). There is a discrepancy between these values and the values reported in Table 2 which are 122°C and 106°C. respectively. Assuming that the samples are identical. the difference should be due to a systematic error, since both of
our measured values are less than theû reported values. This error c m onginate from the
difference in methd of calibration of the instrument or from the procedure of deriving the inflection points of the curves in thermograms for Tg determinations.
The rneasured Tg's seerned to be far enough apart to brin$ about t h c d relaxation. Thermal treatment to activate thermal relaxation was performed in the hot-
stage mounted on the optical microscope. Sample 82 was chosen for this purpose, since the contracting component was the copolymer (the component with lower Tg) and wodd
show dispersed phases of the copolymer in the PMMA maau<. The sample was annealeci in the hot stage at 112OC for six hours. Optical microscopy observations showed some
limitect enhancement of the phase boundaries caused by thermal relaxation. However, it was not encwgh to allow a quantitative assessrnent of the phase morphology to be made
(Figure A- 14). SEM imaging at high magnifications cauxd decomposition and c r a c b g of
the sarnple (Figure A- 16). Rapid imaging at 3k rnagnification caused no decomposition
and resulted in the disappearance of the most of the microtome traces, but did not reveal the phase hi!unciaries of the separated phases (Figure ,445). This method was therefore discontinued. This sample was not imaged with the STM.
5.2.6. Electron irradiation
While studying the fracture surfaces with the electron microscope, it was found
that samples with high PMMA content undergo deformation as a result of irradiation with
the electron beam. This deformation appears in the form of distortions, swelling and blistering cif the surface of the samples (Figurcs A-55 to A-65 and A-104). Similar observations have already k e n reported in the literature'? These observations initiated the
idea of obtaining a phase contrast by decomposing the PMMA phase while leaving the
other phase unchangedh'. The decomposition of one of the phases by the electron bcam
67
would not reveal the morphology of samples in form of blocks, since the electron beam
penetrates intri the sample for a few hundred nanometers and can damage the surface of
the samples due the softness of the polymeric material. This can occur as a result of
generation of the gaseous decomposition products in the inner bulk of the sample which
can destroy the features on the surface by blowing them up (Figure A-104). However, it
was possible ta image the samples which were in the form of thin slices (Figures A-112).
Judging from the previous SEM images, the dimensions of the morphological
features were expected to be between 100 nm to 900 nm. Therefore, slices with 200 nm
thickness would be suitable for the purpose of revealing the structure by electron
irradiation. Slices were mounted on an SEM stub by mcms of a double sided adhesivt
tape and were made conductive by the gold sputtering. This methoci of scanning the
coated slices workecl very well for the mid and high styrene containhg blends sarnples.
esp ia l ly the samples from 84 to 88 (Figures A-1 17 to A-132). Strangely enough, oniy
those parts of the slices that had certain distances from the base adhesive tape (about tens
of microns). and neither flat lying nor sticking out parts underwent decomposition
(probably due to a suitable combination of heat dissipation possibility and the electron
scattering at different p~in ts of the slices)(Figures A-142 and A-148).
5.2.7. Natural Contrast
With the advent of the STM technique, it was found that sirnply rnicrotorning of
the polymer bIends (with no further treaunent) creates surfaces with topographie features
that represent the phase structure. This naturally occurring phase contrast was already
ctetected in the optical microscc~py by observing round spots on the h s h l y microtomed
surfaces of blend samples (Figure A-3). However, their extremely smaii sizes precluded
any quantitative evaluation of the phase domain sizes and any conclusions about their morphology. Unfcwtunately. the high magnification power of SEM did not help to improve
the observations, because it was not possible to focus the electron beam on the very
smooth microtcimed surfaces. Even the features observed by the opticai rnicroscopy could
not be reproduced with the SEM technique (compare Figures A-7 with A-8, and A-14 with A-15). Later, when the STM was employed. its clear images proved that there is a
68
natural phase contrast between the phases due to the differences in their heights, even in
freshly microtcirned sarnples. It was observed that the height differences of the phases have
a limited value of up to about 10 nm (Figures A-221 and A-222). This small vertical
distance was enou@ to be detected by the STM, which works at rnild conditions and causes no damage to the samples at high rnapifications, even though a smooth coverage
of gold (less than 4 nm thick) was necessary.
One possible explanation of this phase contrast is that it could be the result of
moisture absorbed frtim the surrounding air, and therefore, to be a solvent relaxation
effect- Ln this case, the moisture would shrink the PMMA containhg phase, which indeed takes place. as can be seen in the STM images. However, since the hshly rnicrotomed
surfaces also showed this contraction effect (while the ambient relative humidity was d y
35%. and soon after microtoming,, a vacuum of 0.1 mbar was applied during the gold
coating,), the effect can hardly be attributed to the absorption of moisture.
A more reasnnable explanation is that the difference in the mechanical properties
(i.e. stiffness or the mtduli of elasticity and the elongation at break) of the two
comptinents is the cause of this phase contrast effect. If a block of a polymer that contains
separate phases with different mechanical properties is cut, the s w e r component (Le. the
one with higher intniulus or the one with higher elongation at break) would have a lower
height than the other component. It c m be observed in all of the microtomed samples, that
PMMA has the lower height than the copolymer. This is in consistent with the data from
~ u k a n s r k ~ ' s ~ ~ report which shows that PMMA has both higher modulus (3.19 GPa) and higher elongation at break (7.1%) than the copolymers. This c m be seen e.g. in sample
811) which has a mtdulus of 2.78 GPa and an elongation at break of 2.5%.
5.3. Optical Microscopy
The fust tool that was employed in the study of the morphology of microtomecl surfaces was the optical microscope. In sample 89, tiny blister shape features identifieci as the dispersions of PMMA in the copolyrner matrix were observed at the maximum
possible magnification (x 1000 by eye piece and x1500 on the photographs) (Figure A-3).
69 Other exampies in the series 80 showed wavy features which were more populated with these blisters for the bleds with volume fractions closer to 0.5. Generaiiy speaking, the
features were too small to be measured (-1 p), however, it was possible to distinguish
the features of the surface by using the Nomurski inteflerence contrust technique.
Optical micmscopy required a very fiat level surfaces especiaüy at higher magni fications. as requi rements for field depth. Although the fracture surfaces probably had more features tii study. it was not possible to focus the light on a wide enough area on
the fracture surfaces (Figure A-13). Slices rnicrotorned ffom the blocks of samples were
studied both in the bright field and in the interference connast modes. As expected, the
latter produced much better pictures, dthough in general, the technique is lirnited by the low rnagnification power and from the low depth of field (Figures A-113 to A-116).
Therefore, more piiwerful triols were sought and the first candidate was the SEM.
5.4. Scanning Electron Microscopy
The purpose of employing the electron microscope was to take the advantap of
its high rnagnification power for investigating microtorned samples, and to extend the observations from the optical microscope. The SEM mode has k e n used extensively in studying the fi-ucvwc. surfaces of solid pdymers and blends63. The TEM mode on the
other hand, has been ernployed in a more complicated way to investigate the phase
structure of pdyrners in frinn of ultra-thin sections, especially after the work of J. S. ~ r e n t ~ un staining of pol ymer samples by heavy metalcontaining chemicals.
Of the twci electnin rnicroscopy techniques, the SEM was chosen due to its
relative simplicity compared to the TEM, which required cryo-microtomhg of the samples
into ultra thin sections and finding a selective staining reagent. Later, the idea of using TEM was completely abandoned in view of the much easier and more effective techniques
of the SPM. The x-ray mode of the electron microscope was also tried. In an attempt to
produce the elemental map of the surface for oxygen, a microtomed and graphite-coated
surface was imaged. There are three elements of carbon, hydrogen, and oxygen
70
throughout the sample. but oxygen is only contained in the M M A monomer uni@ (-CH,- CH(CH3)(COOCHI)-), whiçh could be a basis for contrasting the PMMA phase against
the other phase. This approach, however, was not successfiii because of the low
percentage of O even in the O rich domains of PMMA (two O in five C and nine H) (Figures A-43 and A-44).
Surprisingly. when usine the SEM, the features on the microtomed surfaces were difficult (and in sorne ca.ses impossible) to focus on and the image quality was worse than was obtained by the optical microscope. Only the traces of the cutting knives left on the
roughly rnicrotorned surfaces could be found and irnaged. A block of sample 810 (the pure copolymer 80:20) was rnicrotorned and imaged to distinguish the knife-created artifacts
from the morphciiogical features sought in the other samples (Figure A- 1).
In order tci be able to better focus the electron bearn on the surface, it was decided
to replace the flatly microtomed surfaces with the more rugged surfaces fkom the fracturing. The idea worked well and good images could be obtained from the fiacture surfaces of sarnpie 89 (Figures AI1 and A-12). For more reliability of the observed
morphologies, a hiad sarnpfe, i.e. sample 810, was aiso imaged. (Figure A-33 and A-34).
The reproduci bility of the features was ascertained by imaging several diierent fracture
surfaces and ccimpüring them visually and quantitatively (Figures A- 17 to A-24).
The next step was to systernatidy image the rest of the samples. A complete set of the samples of series 80 (80:20 copolymer) was prepared by fracturing in Liquid
nitrogen. Very gucid image quality was obtained for sample 89, 88, 87, and 86 with this method. However, two kinds of limitation restricted the applicability of the method to the
ottier samples.
One limitation arose from the interface forces at the boundaries of the phases. In sorne samples cracks propagate through the phase boundary as a result of the weak
interfacial forces, and cause an easier separation of phases (Figures A-3 1, A-32, and A-37
to A-42). In others, cracks propagate across the phases and result in no trace of phase boundaries (Figures A-26 to A-30). The other Limitation was brought about by the
71
decompvsition of the samples under the influence of the electron beam. During the
anempts to search for morphological features at higher magnifications, some spots,
especially on the samples of high PMMA-content, started to decompose (Figures A-54 to
A-65). This effect was not observed in samples with high styrene, or less MMA content,
even in high magnifications (Figures A-66 to A-7 1, and A-83 to A-86).
Several techniques including irradiating with different acceleration voltages and
different exposure tirnes. were used to image the sarnples without decomposition (and therefore destruction) of their surfaces. In case of the soft samples, i.e. those with hi@
MMA content. the copdymer also experienced decomposition. For these sarnples, rapid
irnaging at low magnifications was tried. but this did not give any valuable information at
al1 (Figures A-87 to A-93). Hawever. the idea of irnaging at lower electron acœleration
voltages was very hitful. The latter attempt stopped the decomposition of the samples
and permitted us to image a wide range of compositions, but, since the b l e d components
were more compatible in these sarnples, no appreciable morphology was discemible
(Figures A-94 to A- 107).
Observing the decornposition of the PMMA phase initiated the idea to reved the
morphology by irraciiating the samples with electron beam In the first attempt, sample
blwks with fracture surfaces were med. The enhancement of the features was not
appreciable, and almost the same information as before was obtained (Figure A-72 to A-
86) . In another attempt, samples were prepared in the form of slices for imagine. This tirne excellent STM images were obtained. Thin siices of the sampies were exposed to the
electron beam in an optimum condition of voltage and irradiation tirne. The PMMA phase
decomposed off (or shrdnk), and left a sample surface with enhanced phase boundaries.
These images resulted in a clear view of the morphologies of the separated phases in the
blend sarnples that such a phase separation was expected (Le. not very transparent
samples) (Figures A- 1 152 to A- 150).
5.4.1. Interpretation of the SEM Images
The images of the m m d surfaces, both blocks and slices, are quite self
explanatory. Regardless of the knife traces, the features simply represent the different
phases in the polymer blends, evident from the correlation of the volume fractions with the
relative areas of the phase domains in the images. However, for the fracnue surfaçes, the
images are more complicated. In fracture images such as Figures A-1 1 and A-1 11, the
observeci line features are attributed to the craze residues which are ductile breaks of the
craze bounciaries. These crazes are the precursors of the propagating crack that has
resulted in the fracture failure. The coarseness and the height of the craze residues are proportional to the degree of ductile fracture (compare the more ductile fracture in Figure
A- l 1 with the more brittle fracture in Figure A-12).
ln the pictures of the fracture surfaces of high styrene samples such as those
mentioneci above. snme uval shape features are distinguishable. These features can be
attributed to the PMMA phase dispersed in the copolyrner rnaaix. The crescents around
some of these oval features indicate that the dispersed phase is loosely connected to the
matrix. If the PMMA domains were large enough to fül out the cavity, then the interface
forces would be much larger and the mechanical strength of the blend would be much
bette$? Some of the «vals are shallow, which indicates that the dispersed phase has been rerncived. There are also bright ovals which obviously are particles of PMMA ernerwg
out of the surface. The number of these particles varies from picture to picture, which can
be related to the m d e of fracture in each sarnple. The average size of these particles is a
little bit smaller than the flat ovals, as will be discussed later. Other non-round bright
pieces emerging frtim the bottom of some ovals can be attributed to the residues of the
ductile breakage of PMMA dispersed particles. In Figure A-84 there is a feature that
resembles the resirlue of the blast of the gold coating as a result of the deçomposition of
the dispersed particle. The srnall features (about 30 nm) in Figures A-107 and A-108 can
be attribut4 to the grain boundaries of the gold coadng.
S.S. Scanning Tunneling Microscopy
Decomposition of PMMA under a high voltage electron beam restricts the
usefulness of the elecuon microscopy to only a few samples with a hi@ content of
styrene. The scanning probe microscopy (SPM), on the other hand. is potentialy a good alternative to the SEM, since it has miId operating conditions. Among the different
techniques of the SPM, the STM was rnost suitable to start with.
5.5.1. Burleigh instructional STM
This STM instrument was chosen first due to its simplicity of operation. Obviously
the sarnples needed conductive coating, and therefore gold sputtering was a suitable option for this purpose. First the fractured samples that were used in the SEM experirnents
were tried. The surfaces were too rough to be scanned. It seemed that the movement of the tip in the 2-direction was too slow to be able to follow the heights of the features. This
~ s u l t e d in a frequent bumping of the tip on the surface. However, occasionally some
promising features were observed which irrrplied that by optimizing the scanning parameters and using very flat surfaces. good images could be taken.
Excellent images of the microtomed surfaces could be taken by the STM. After
optimizing the scanning parameters (such as scan rate, bias voltage and tunneling current)
and by etching sharp tips, a wide range of samples, including a complete senes of the
opaque samples, could be scanned (Figures A453 to A-183). About 250 images that
showed interpretable features were coilected. Because they occupied a large volume of
computer inemory (about 120k for each), they were screened down, and in the end about
100 images were archived. The images were saved as raw data with no additional process ing . Howe ver. the photographie pictures were taken from the computer screen
after svrne mincir mcuiifications such as the "plane renroval", and the "confrusting to the
staridur.c/ deviutiort". The software for processine of images such as Fourier
74 transformation and filtering methods on this machine seemd to be quite powerful and versatile, although it was more useful for atomic resolution scannings.
5.5.2. NanoScope II STM
A large number of images from a wide range of samples were produced by this
instrument and about 70 images were chosen and saved. The photographie picaires were taken after processing of the raw data by the "j7attening" and the "fow pass fSlreringW
operations, A complete range of opticaiiy opaque samples were imaged with this
instrument (Figures A-185 to A-225). Not a i i of the totally transparent sarnples were imaged. since they were supposedly homogeneous at the scale of tens of nanometers. They were therefore not expected to show any separated phase features within the lllnits of the
resolution of this method, i.e., the gain size of the gold coaang. In order to provide a
better comparison of images of different samples obtained by different instruments, every sample was imaged at two magnifications: 9000x9000 nm (Figures A-185 to A-190) and
4500x4500 run (Figures A- 194 to A-2 17).
The powerful image processing capability of the NanoScope II provides one with a powerful means for revealing the features of the images as well as precise measurements
for further quantitative calculations. For example. the image of Figure A485 was
reprocessed to give an image with height contour lines (Figure A-218), a three dimensional height view (Figure A-222), a 3D h e plot (Figure A-22 l), and a view of the cross section of the surface to a thickness of about 1 nrn at the average heights. (Figure A-
223).
5.6. Morphology Studies
In order to have a comprehensive idea of morphologies of the samples and to follow the trends of their variations with respect the chemicai compositions, the rnicrographs are illustrated in their reduced size on a chart of two pages. Figures A-224
75 and A-224 display the images of all of the samples at the scan sizes of 9000x9000 and
4500x4500 nm, respectively. The clear phase boundaries of the bottom row indicate the incompatibility of the of the components, i.e. the pure PMMA and the 80% styrene
containing copolymer. The sharpness of the interfaces drop rapidly as the copolyrner
component gains more fraction of MMA, which corresponds to an enhanced compatibility
of the components. For sarnple series 50, the separated phase domains can still be well distinguished in almost al1 of the blend fractions. However, for sarnple series 40 and
particularly for series 30, it is hard to specify a feature unarnbiguously. The fine texture of
the images belong, apparently, to the gold grains, aithough why they show a texture rather than randornness remains a question. The undulations under this texture can be attributed
to the phase separations, although those wavy features that are perpendicular to the
microtome traces may have resulted fkom the crazes created at cutting or from the stick-
slip of the knife.
The types of observed morphologies are in agreement with Cahn's theory of phase
separation discussed in the theory part of this thesis. Moving f b m the right to the left of
Figure A-224, one can see the foliowing morphologies for sample senes 80: Samples
89.88, and 87 have the dispersed-phase-in-the matrix morphology. At around sample 86 some droplets combine and create phase inclusions in the shape of distorted cyiinders. This
is called the percolation Iimit, beyond which spinodal decomposition takes place. The
spinodal decomposition leads to the cocontinuous morphology wwhich is obvious in samples 85 and 84. Here, the interpenetrating phases have the same thicknesses and are
called luniellur cocontirtuour ntorphology. Sample 83 has also cocontinuous morphology,
but the thickness of the copolyrner phase has decreased considerably . This is a typicd
sample with Jibrillur cocontinuous niorphology. The fibrillar phase is cocontinuous in one
direction, but its section seems like dispersed phase. The features in image of sample 82
can be attributed to the other limit of the percolation morphology. Sample 81 has the
morphology of the dispersed copolyrner phase in the PMMA matrix. For sarnple series 50, the same trend of changes can be deduced but with narrower composition range of
cocontinuity. Sample 44 shows an obvious domain-rnatrix morphology. which is an indication of the narruwing of the cocontinuity range.
There is an overall agreement between the nsults of this study and those from the 46
DKI . except that our results do not show symmetric phase transition points around the
76
5050 b l e d composition (@=0.5) point, rather, the whole cocontinuous morphology lays in the range: O< $ < 0.5
Size Distribution Studies
in the following discussion, for convenience, the "dispersed phase domains in the
matrix phase" are referred to as "particles".
The correlation of the morphology with the composition of the blend samples is obvious h m the figures A-225 and A-226. in order to be able to derive quantitative
relationships between the morphology with the physical properties of the blends, it is
necessary to express these correlations in ternis of nwnerical values. This quantification.
though, can not be very accurate and precise because of the diversity in the shapes and the
inconsistency in the sizes of the phase domains. However, the assessrnent can be done
semiquantitatively by investigating e.g. the trend of the particle size changes among the
samples that have similar particle shapes. As seen in their images, samples with high copolymer contents do have such a morphology, and therefore their images can be
analyzed From this point of view.
For size evaluation studies, oniy the samples 89, 88, 59, and 58 with dispersed
phase-in-matrix rnorphology (with phase domains of weli defined boundaries and
approximately round shapes) were considered. At first, the size distribution histograms
were plotted for different samples. then an average size was assigned for each sample.
Later, these average sizes were used to estirnate trends of the variation of sizes with
compositions. Different methods were used to masure the particle sizes of the features
depending on the type of the images, Le., the images from either the SEM or the STM.
5.7.1. SEM Data
SEM images from seven fracture surfaces of the sample 89 were analyzed and their
s i x distribution histograms were plotted both individually (e.g. Figure A-226). and in surn (Figure A-229). In fracture images, two types of features can be attributed to the
dispersed particles (Figures A-17 to A-24): the brighter features represent particles protruding out of the surface, and the darker features represent traces of particles
withdrawn from the surface. In their histoprns, the latter is shown in solid bars (Figure
A-226), and the frmner in hatched bars (Figure A-227). Figwes A-229 and A-230 are
plots of data obtained by summing the data ftorn seven images (Figures A-17 to A-23).
Figure A-231 is a second plot of Figure A-230, but with the data smoothened to 3 channels. This histogram dearly suggests a bimodal size distribution for the darker particles with the averages of 165 nm and 363 nm (the overaii average is 349 nm), and a
monomalal size distribution for the btighter particles with the peak at 165 nrn and the
overail average of 265 nrn. The bimdality of the size distribution in some of the samples can be attributed to the fact that a larger particle is formed from a coalescence of two
smaller particles.
It seems that the rneasured sizes, both for the particies and the cavities are (to a lirnited extent) smaller than the actual particle sizes. The particles (the bright spots), might
have experienced elongaticin, and therefore tfünning, at the rime of breaking- Therefore it
is possible that the cavities (the darker spots) are not eue replications of the whole
dispersed particles. However, this uncenainty is not very large, since nearly theû actuai sizes are captured in the spots with crescent shape openings. These openings are at the interface of the dispersed particles with the matrix. and their presence indicates a weakness
of the linkages between the two phases. The inner diameter of the crescent represents the
size of the particles, and its outer diarneter is an indication of the size of the cavities. These sizes are in good agreement with the sizes of the bright and the darker spots discussed
before.
SEM images of the from samples 89. 88. 58 and 59 were also clear enough to be ana1yzec.i. The method of measurement ernployed was the sarne as that
used fur the fracture SEM images. The accuracy of measurement was the same, but some
uncertainty was assriciated with the definition of the phase boundaries. The observed
features were due to the decomposition of the particles, and therefore the boundaries
might have experienced different deformations (depending on the diarneter of the particle with respect to the thickness of the slice). However, the average sizes were just slightly larger than the data obüiined for the samples prepared by fractuxing (266 nm versus 230 nrn for sampie 89).
78
Figure A-232 is the histogram of the data obtained fiom the image of Figure A-
133 (sarnple 59). The histogram in Figure A-233 is plotted for the data fkom 4 such
images. Figure A-234 is a histogam plotted from the data obtained from Figure A-139
(sample 58). and the sum of data from 5 such images produced the h i s togm of Figure A-
235. The histopam of Figure A-236 is made f3om the data obtained fiom the image of Figure 129 (sarnple 89). and a sum of 3 such images producd the histogam in Figure A- 237. And finally. the histogram of Figure A-238 is plotted from the data obtained from the
image of Figure A-126 (sample 88), and the sum of data from 4 such images nsulted in
the histogram cif Figure A-239.
Here again, a bimcdal distribution of the particle sizes of the dispersed phase could
be assigned. especiülly for sarnple 88 (Figures A-238 and A-239). In addition, the results
of the analysis revealed that the average s i x of the features changed regularly with the composition of the polyrner. As seen in the Table 4, decreasing the volume fraction of the
copolyrner in the b led h m 90% to 80% (moving from sample 89 to 88) doubles the size
of the dispersed phase. and decreasing the styrene content of the copolyrner fiom 80% to
50% (moving from sample 89 to 59) thirds the s ix .
Table 4. Dcpcndcncc of average sizes of the dispersed phases obtained from SEM
images on the composition of the blends.
5.7.2. STM Data
The data obtained from this technique is more reliable than for SEM. since the
instrument rneasures the s i x of the features dinctly. and the boundary of the features are
welI defined. However. uncertainty arises fiom the ambiguity that it is not known whether
the observed differences in the sizes of the features originate from the particles of cisennt
sizes or from different sections of the particles of the same s k obtained during microtoming. This can not be ascertained. SNdying the cross sections of the features of
the images sugpsts that, during microtoming apparently. the small particles leave the
rnicrotomed surfaces completely. which resulu in creaîion of an opening with the
maximum diameter of the particle or even larger. The larger particles. on the other hand.
show a flat bottom. which rneans that a major part of the particle is dl nmaining in the
rnicrotomed block. Therefore. it can be concluded that cons ide~g the level of precision
of the microtome and the accuracy of masurement, the observed features npresent the
actual phase domains of the blend samples. The eliipsoid shapes of the particles were
approximated by circles and their diameters were measured on screen by the software as
the distance of two diagonal points. The data coiiected were then used to plot the size
distribution histograms by means of "Cricket Graph" software on a Macintosh cornputer.
Histograms of the particle size distribution of samples 58. 59, 88. and 89 are
illustrated in the following Figures: Figure A-240 was plotted fiom the image of the Figure A-204 (sample SR). and Figure A-241 from the sum of 2 images of this kind. Figure A-242
was plotted from the Figure A-203(sarnple 59). and Figure A-243 from the surn of 3 of
such images. Figure A-244 was plotted fiom the Figure A-186 (sarnple 88) and Figure A-
245 from the sum of 3 of such images. Fmally, Figure A-246 (sarnple 89). was plotted
fiom the sample A- 1x5. and Figure A-247 from the sum of 3 images of such End.
The results of particle size studies reveal that the particle size distribution is approximately munomcdal for sample series 50 (Figures A-241 and A-242), and the
average partiçle sizes, as depicted in table 5. do not differ largely fiom one blend
composition to the other (181 nm versus 154 nm). However. for sample series 80 the
distribution is bi-modal (Figures A-237 and A-239). and the average particle sizcs differ
80 substmtially for the sarne difference in the bled composition. (for example, in 5 1 1 nm
versus 419 nm, the average from the main part of the histopam is 340 nm: the difference is as a result of a few extra large particles observed in right hand tail of the tustogram.)
However. the generdl trend is the same as in the case of the SEM images. The average
particle sizes for fuur samples are given in the Table 5.
Table 5. Dcpendcncc of average sizes of the disperseci phases on the composition of the
blends obtained from STM images.
A cornparison of the results from the two imagine techniques shows that STM gives Iarger average particle sizes than SEM. However, the former is more reliable than the latter because of the weU defmed phase boundaries, and because of the direct
measurement in the STM. The precision of measurernent in STM is better than 20 nm,
while, in case of the SEM, the rneasured values are some 25% less than those fkom the
STM, most probably due to the iîi-defined phase boundaries, as discussed before. In expressing the data as average sizes, it must be noticed that the averages are visually derived frorn more or less multimodal distribution histograms. Therefore, expressing the
results in the form of size distribution histograms is much more informative than assigning
a single value as the average size.
58
181
-
Sample
Site (nm)
Optical Property Studies
The optical pmperties of the sarnples of this study have been investigated at CRIC in Hungary, and some of their results are illustrated in Figures A-252 and A-253 (ref. 57).
7
-
88
51 1
89
41 9
59
1 54
8 1 The high opacity of the sarnpks with even b l e d compositions (Le. 4~0 .5 ) can be
correlated with the higher coarseness of the separateci phase domains observed in their
rnorphology studies. As mentioned earlier, due to the wide spread of the particle sizes, it is not easy to find a qlrarlrirotive relationshîp between the phase domain sizes and the
properties. Figures A-250 and A-251 illustrate the histograms of the sizes of the phase
domains versus the blend composition. The solid bars represent the diameter of the
PMMA particles or the distance of two copolymer phase dornains, while the hatched bars
are the distances of the PMMA particles from each other or the diameter of the copolymer
strands. Both of the histograms show relatively higher coarseness of the phase domains for
the even biend compositions, but the spatial distribution of pamfles seem to be different in
the two histograms.
Figure A-251 shows the dependence of turbidity of sample series 40 on the
wavelength of light. Unfortunately, this series did not show welldefined phase boundaries
in their images. therefore, size correlation can not be concluded for this series. in these
samples (which have weak phase separation due to the stronpr interface forces) it seerns
that the separation is a kind of spinodal decomposition. which keeps a fine texture of the
phases and increases the difference in the amplitude of the concentration fluctuations.
Therefore. the obsewed wavelengthcomposition dependencies can be explained by the
dependency of the wavelengh to the refractive index, rather than to the phase dornain sizes.
Conclusion
The main goal of this thesis work was to study the morphologies of the separated phases in the title polymer blends by means of suitable methods, especiaily the SPM. Since
the conventional methais were inadequate for studyinp the specific materials of this work,
a considerable effort was devoted to finding suitable methods to reveal the phase structures, which makes the thesis to be an application-oriented kind of work.
Good results were obtained in estabiishing suitable methods for studying the title
material. which can also be employed for the study of the morphologies of various types of
blends. Some advances in the imaging methcd were achieved for the first time. These
achievements çan pmvide alternatives in imaging difficult samples that fail in producing
satisfactory results by conventional methds.
A systematic study was performed both in the method of phase contrasting and in
the methoci of imaging phase dornains. Different methods of phase contrasting were
tested, and their usefulness was discussed in detail. The etching method was not good,
because of the damap that was created in the complementary phase by the etching
reagent. The method of enhancement of the phase conaast by means of the solvent and
the thermal relaxations was not useful due to lack of selective solvents and to the
proximity of the g las transition temperatures of the components. The rnethod of freezc- fracturing gave good results only for the blends with considerable incompatibility, Le. the
samples with the overall styrene contents of more than 75%.
A new methd of SEM irnaging suitable for blends with components sensitive to
the etectron beam. was employed. The PMMA phase undergoes decomposition under the
high voltage electron beam. therefore thin sliœs (200 nm) of the samples were irradiated and their phase structures were reveaied. A similar method has been used with TEM
83 technique by using ultra thin sections of the samples. The developed method in this work,
however, can be advantageous for those who do not have access to the more expensive techniques of the TEM with the cryogenic ultramicrotome. The developed method
extended the imaping capability to the blends with the overail styrene content of above
40%.
Another new method that was developed in this thesis work is the application of
the STM technique to study the morphology of the separated phases in polymer blends. In this rnethod, the surface of the precisely microtorned sarnple was made conductive by gold
sputtering. then scanned by the STM in its height mode of operation. The images were
excellent, and with this method, ail of the sarnples with different compositions could be imaged and discernible features were observed in the samples with the overail styrene
contents of above 25%.
The observed morphology of the blend sarnples was in agreement with Cahn's
theory of phase separation in irnmiscible blends, discussed in the theory section of this thesis. For the samples with copolymers of 80% styrene, the dependence of the
morpholcigy on the copolyrner volume fraction, 0, was as follows: For @=O. 1,0.7,0.8, and 0.9. the morpholopy is the dispersed-phase-in-the-matrix type; @= 0.2 and @=0.6 are the
percolation lirnits where the domains of the dispersed phase coalesce; for 9 4 . 3 the
morphology is fibrillar cocontinuous type, and for @= 0.4 and @ 4 5 , the morphology is the
lamellar cocontinuous type. The sarne trend of morphology changes was observed for the
samples with copolymer composition of 50% styrene. Samples with lower styrene
containing copolymers are almost transparent and do not show sharply separated phases in
the 1 imit of resolutiun of the employed techniques.
Size studies reveriled a close correlation between the turbidity and the size of the
phase domains for the highly turbid sarnple series. Because of the divenity and inconsistency of the shapes of the phase domains, it is not possible to conclude a quantitative correlation between the turbidity and the size. However, sorne qualitative
assessrnent can be deduced. Sarnples with domains sizes larger than about 250 nm are completely opaque, whife those with sizes about 150 nrn are about 40% transparent. Size
84 studies showed a bimodal size distribution for some samples. The average domain s h s for the samples with @=O.Y and $&.8 were 340 run and 520 nm for 808 styrene copolymer, and 150 nm and 170 nm for 50% styrene copolymers, respectively. As a result of the
nature of the shapes and the large difference in the sizes, the uncertainty in the above
values is estimated to be about 20%.
Outlook
The work presented here opens a new window to study the phase structure of
pol ymer blends. De tailed studies of morphology-property relationships can be based on the results obtained by the methods developed for the specific polymer system of this work- It is possible to find a quantitative relationship between the transparency of the
polymer blends for different wavelengths with size, shape, and refracave index of the phase domains. This can be achieved by employing powerful image analysis software that produces the size data more easily and more reiiably. The same quantitative evaluation is needed for the mechanical properties with respect to the morphology of the blend phases.
Still there is room to irnprove STM imaging of polymer blend samples. The ongin
of the fine textures observed in the more transparent samples is not assured. The reason of the natural phase contrast in microtomed samples (which was the basis for the STM imaging iiî ihis work) is not weU discussed and understood. .4 more detailed snidy of the
conductive coat grain structure is usefd in dis~guishing the real feahnes at high magnifications STM imaging. Another irnprovement would result from cryomicrotoming of the samples. and a new attempt to study both the sotvent and the thermal relaxation with the STM seems worthy.
The AFM technique with its various modes of operation is another promising tool
which wouid t« further expand the ability to image more transparent samples. The tapping mode AFM gives many more details of the surfaces with higher resolution, and the friction mode AFM differentiates between phase domains with slightly different elasticities.
Indeed. in the very last days of writing this thesis, a few images of this type were taken,
but it was too late to optimize the imaging parameters and draw relevant conclusions.
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9. Images and Grapbs
9.1. Images
Figure A-1, SEM image of sample 810 (pure 80:20 copolyrner). Trace of knife on a microtomed surface
Figure A-2. SEM image of sample 85. Surface of a microtomed block after wo days of contact with rnethanol.
I I Figure A-3. Optical rnicrograph of sample 89. Sutface of a rnicrotomed block wilhoui further treatmenl.
Figure A-4. Optical micrograph of sample 89. Surfixe of a micmomed block after etching with 10% acetic acid for 1 minute.
Eigure A-9. SEM image of sample 89. Figure A-IO. SEM image of sampie 89. Surface of a microtomed block after Surfixe of the sample fractured at room etchino with 10% acetic acid for 10 temperature. minutes.
Figure A-Il. SEM image of sample 89. Figure A-12. SEM image of sample 89. Surface of the sample hctured in liquid Surface of the sample fractured in iiquid ni trogen. niuogen.
Figure A-13. Optical micrograph of sarnple 89. Surfxe of the sarnple hctured in liquid niirogen.
Figure A-14. Opticd micrograph of sample 89. Sudace of a microtomed bloçk after themal etching.
Figure A-15. S E M image of sample 89. Surface of a rnicrotomed blmk after thermal etchhg. Same sarnple as in Fig. 14.
Figure A-16. SEM image of sarnple 89. Surface of a microiomed block after thermal etching. Cracks are caused by irradiation. Same sarnple as in Fig. A- 15.
Figure A-17. SEM image of sample 89. Surface of the sarnple fractured in liquid nitrogen.
Figure A-18. SEM image of sarnple 89. Surfxe of the sample bacnired in liquid nitmgen.
Figure A-19. SEM image of sample 89. Surface of the sample fracnired in liquid ni trogen.
Figure A-20. SEM image of sample 89. Surface of the sample frartured in liquid nitrogen.
Figure A-21. SEM image of sample 89. Figure A-22. SEM image of sample 89. Surface of the sample frac& in liquid Surface of the sample fractured in liquid nitrogen. niaogen.
Figure A-23. SEM image of sample 89. F i u n A-24. SEM image of sample 89. Surface of the sample Eractureû in Nuid Surface of the sample fractured in liquid nitrogen. nimgen.
Figure A-25. SEM image of sample 81. Surface of the sample fractured in liquid niuogen. Magnification is XI00
Figure A-26. SEM image of sample 81. Surface of the sarnple hctured in liquid nitrogen. Sarne sample as Fig. A-25 with X3000.
Figure A-27. SEM image of sample 82. Surface of the sample fractureâ in liquid nitrogen.
Figure A-28. SEM image of sample 83. Surface of the sample fractured in liquid nitrogen. The hole is caused by irradiation.
Figure A-29- SEM image of sarnple 84. Figure A-30. SEM image of sample 85. Surface of the sample fractureci in liquid Surfxe of the sample Fractureci in liquid niuogen. nitrogen. The holes are caused by
irradiation,
Figure A-31. SEM image of sample 86, Surface of the sample fractured in tiquid nitrogen.
Figure A-32. SEM image of sample 87. Surface of the sample fractured in Liquid ni trogen.
Figure A-33. SEM image of sample 810 Figure A-34. SEM image of sample 810 (pwe copolymer). Surface of the sample (pure copolymer). Surface of the sample fractured in iiquid nimgen. Magnification frac tured in liquid N trogen. Magnification is Xlûûû. is Xlûûûû.
Figure A-35. SEM image of sample 84. Figure A-36. SEM image of sample 86. Surface of the sample Eractured in liquid Surfiace of sample the fractured in liquid nitrogen. Magnification is X 1000. nitmgen.
Figure A-37. SEM image of sarnple 87. Figure A-38. SEM image of simple 87. Surface of the sarnpie fractured in liquid Surface of the sample fractured in liquid nitrogen, nimgen.
Figure A-39. SEM image of sample 88. Surface of the sample fracturai in liquid nitrogen.
F i A-40. SEM image of sample 88. Surfixe of the sampie fractured in iiquid nitmgen.
Figure A 4 1 . SEM image of sarnple #. Surface of the sample fractured in liquid niuogen.
Figure A42. SEM image of sample 89. Surfâce of the sample Eractured in muid niuogen.
Figure A43. SEM image of sample 89. Fgurc A44. Oxygen map of sample 89. Microtomal surfire of a sample Mock The same spot as in Fig. A-43. frozen by spraying liquid nitrogen- Mapification is X 10000.
Figure A 4 5 SEM image of sample 89. Rapidly microtomeci surface of a Mock frozen by spraying liquid nitrogen
Fire A&. SEM image of sample 8.5. Surface of a block scratched by glass in iiquid niuogen.
Figure A-47. SEM image of sample 89. edge of a microtomed-fhctuted surfse of a broken block microtomed at nwmi
temperam.
Figure A48 SEM image of sample 89. Surface of a sample Eractured at room temperature.
Figure A 4 9 SEM image of sample 89. Surface of a sample fractureci at rmm iemperam.
Figure A-50 SEM image of sample 89. Surface of a sample Eractured ai room temperature.
Figure A-51. SEM image of sarnple 89. Rapidly microtomed surface of a Mock frozen in by spraying liquid niuogen, Same sample as Fig. A- 45.
F i A-52. SEM image of sample 89. Rapidly microtomed surface of a block b z e n in by spraying liquid nimgen. S a m sample as Fig . A-5 1.
Figure A-53. SEM image of sample 89. Figure A-54. SEM image of sarnple 89. Same spot as in Fig. A-52. Image was Microtomed sucface of a frozen block. The taken in back scattering mode. dark area is the decompowd area caused
by irradiation.
Figure A-55. SEM image of sample 85. Surface of a bactured sample in liquid nitrogen. Local decomposition is caused by irradiation.
F i A-%. SEM image of sample 85. Mictotomed surface of a h z e n block. The window is created at high magnification by irradiauon.
Figure A-57. SEM image of sample 83. Surface of a fractured sarnple in muid nitmgen. The sample is erisily âecmposed by irradiation.
Eire A-%. SEM image of sample 82. Mimomed surface of a frozen block. Decomposition occm even at bw magnifications. X 1000.
Figure A-59. SEM image of sample 81. Surface of a fractured sample in liquid nimgen. Decomposition occurs even at low magnifications. X100.
F i AaO. SEM image of saniple 58. Surfixe of a fractured sample in liquid nimgen.. Here decomposition is less pronounced.
Figure A b l . SEM image of sample 58. Surface of a fractured sample in muid nitrogen. Here decompositim is less pronounced
Figure A d 2 . SEM image of sarnple 59. Surface of a 6acnired sampie in iiquid nimgen. Here decornposition is less pmnounced.
Figure A d . SEM image of sample 38. Surface of a fracnired sarnple in liquid niuogen. The large hole at the upper centers caused by irradiation.
FIT A-64. SEM image of sample 48. Surface of a fracnired sample in liquid nimgen. The sample melted at high vol rages.
Figure A#. SEM image of sample 49. Surface of a fiactured sample in iiquid niuogen. This composition is relabveiy stable even at high mapification
Fiiure A&. SEM image of sample 58. Surfa~e of a fractured sample in liquid nimgen.
Figure A-67. SEM image of sample 59. Surface of a E r a c t d sample in liquid ni trogen.
F I A-68. SEM image of sample 59. Surface of a fraçîured sample in liquid nitrogen. No decomposition occurs even at the m-cation of X30000.
Figure A-69. SE-M image of sample 88. Surface of a fractured sample in liquid nitrogen. No decomposition occurs.
Fiin A-70. SEM image of sampie 89. SMace of a fractured sarnple in liquid nitrogen. No deçomposition occurs.
Figure A-71. SEM image of sarnple 89. Surface of a Gactured sarnple in muid nitrogen. No decomposition occurs even at the mapification of XS0000.
F i n A-72. SEM image of sample 81. Surface of a fractured sample in liquid ni trogen.
Figure A-73. SEM image of sample 81. Surface of a sarnple 6actured in iiquid nitrogen. Sarne spot as in Figure A-72
F i i r e A-74. SEM image of sample 82. Surface of a sample hctured in Liquid nitrogen.
Figure A-75. SEM image of sample 83. Surface of a fracnired sample in liquid ni trogen.
Figure A-76. SEM image of sample 84. Surfze of a fractured sample in liquid nitrogen.
Figure A-77 SEM image of sarnple 84. Figun A-78. SEM image of sample 85. Sarne spot as Fig. A-76. ïmaged after IO Surface of a fmctured sample in liquid min irradiation . ni trogen.
Figure A-79 SEM image of sample 85 Same spot as in Fig . A-78. Imageci after 1( min irradiation. Some features start tî develop.
F- AISO. SEM image of sample 86. Surfixe of a fractured sample in liquid nimgen.
Figure A-81 SEM image of sample 86. Same spot as in Fig. A-80. imaged afier 10 min irradiation . Some features start to develop.
F i i r e AIS2 SEM image of sample 86. Same spot as in Fig. A-8 1. lmaged after 15 min irradiation . Some features stan to develop. Appearance changes appreciably.
Figure A*. SEM image of sample 87. Surface of a sample fracturai in liquid ni trogen.
F i A*. SEM image of sample 88. Surface of a sample fractured in liquid nitrogen.
Figure A-=. SEM image of sample 89. Surface of a sample fractured in liquid nimgen. No decomposition at XJ0.000
Figure A-86. SEM image of sample 810. Surface of a sample fractured in liquid nitrogen. No decomposition at X50.000
Figure A-87. SEM image of sample 82. Surface of a sample fraciured in liquid nitrogen. Rapid irnaging at XlOW
F i AISS. SEM image of sample 83. Surface of a sample fractured in liquid nimgen. Rapid irnaging at XlOOO
Figure A-. SEM image of sample 84. Surface of a sample fiactureû in liquid nitrogen. Rapid imagine at XI000
Figure A-90. SEM image of sample 85. Surface of a sample fractured in Iiquid nitrogen. Rapid imaging at Xlûûû
Figure A-91. SEM image of sample 86. Surface of a sample fracîured in liquid nitrogen. Rapid imaging at XlOO
F i A-92. SEM image of sample 87. Surface of a sarnple fractured in liquid nitrogen. Rapid imaging at Xlûûû
Figure A-93. SEM image of sample 88. Figure A-94. SEM image of sample 54. Surface of a sample bacnired in liquid Surface of a sample fractured in liquid niuogen. Rapid imaging at X loû nitrogen. Low voltage imaging at kV.
Figure A-95 SEM image of sample 57. Surface of a sample fractured in liquid nitrogen. Low voltage imaging at kV.
F i i r e A-%. SEM image of sample 58. Surface of a sample fractured in liquid nitrogen. Low voltage imaging at kV.
Figure A-97. SEM image of sample 59. Surface of a sample fractured in liquid nitrogen. Low voltage irnaging at kV.
Figure A-98. SEM image of sample 52. Surface of a sample fractured in tiquid nimgen. Low voltage Unaging at kV.
Figure A-99. SEM image of sarnple 53. Figure A-100. SEM image of sample 54. Surface of a sample frûcnired in liquid Surface of a sample fractured in liquid nitrogen. Low voltage imaging at kV. nimgen. Low voltage irnaging at kV.
Figure A-101. SEM image of sample 56. Surface of a sarnple fnctured in liquid nitrogen. Low voltage imaging at kV.
Figure A-102. SEM image of sample 47. Surface of a sample frachired in liquid niuogen. Low voltage imaging at 10 kV.
Figure A-103. SEM image of sample 30 (pure PMMA). Surface of a sample fractured in liquid nitrogen.
F- A-104. SEM image of sample 31 0 (pure 30:70 copolymer). Surface of a sarnple fractured in tiquid nimgen. The sensitivity to eleçtron beam is demonstrated.
Figure A-105. SEM image of sample 310 (plue 30:70 copoiymer). The same sample as in Fig. A-104 h g e d by low voltage electrons. at the rnagnif~cation of X.OW.
F in A-106. SEM image of sarnple SI0 (pure 50.50 copoiymer). Surface of a sample fractured in Iiquid nitmgen.
Figure A-107. SEM image of sample 51 0 (pure 50.50 copolymer). Same sample as in Fig. A-106 imaged at high voiiage and mapificarion. Gold particles?
Fiin A - l a . SEM image of sample 81 0 (pure 80:20 copolymer). Surface of a sample fractured in liquid nitrogen. imaged at high voltage and magnificaîion.
Figure A-109. SEM image of sample 88. Micrororned surface of a sample block frozen in by spraying Liquid nimgen.
F i t A-110. SEM image of sample 88. Surface of a sample frac& in liquid nimgen. Compare with Fig. A- 109.
Figure A-11 1. SEM image of sample 88. Swface of a sample fracnired in room temperame. Compare with Fig. A-1 10.
Fiin A-112. SEM image of sample 88. Surface of a 200 nm slice sample microtomed at room temperature. Feanrres cieveloped by irradiation. Compare with Fig. A- 109, to A- 1 1 1.
10 pm
Figure A-113. Optical micropph of sample 89. Sinface of a 500 nm slice microtomed at m m
u Figure A-115. Optical micropph of sample 88. Surface of a 900 nm slice micraomed at room temperature. Sarne sample as Fin. A- 1 14 with different focusùin.
4 4 Figure A-116. Optical micmgraph of sample 88. Surface of a 200 MI slice microtomed at room temperature.
Figure A-117. SEM image of sarnple 81. Surface of a 300 nm slice sample microtome. at room temperature
F~gurc A-1 18. SEM image of sample 82. Surface of a 300 nrn slice sample microtomed at m m temperaîwe
Figure A-119. SEM image of sample 83. Surface of a 300 nm sfice sample microtomed at room tempçrahire
F i A-12û. SEM image of sample 84. Surface of a 300 nm slice sample microtomed at rom temperaime
Figure A-121. SEM image of sample 85. Figiire A-122. SEM image of sample 85. Surface of a 300 nrn slice sarnple Surface of a 300 nm stice sampie rnicrotomed at room temperanrte rnicrotomed at rmm temperature
Figure A-123. SEM image of sample 8 Surface of a 300 nm slice sarnp microtomed at room temperature
Figure A-124. SEM image of sample 86. Surface of a 300 nm slice sample microtomed at room temperame
Figure A-125. SEM image of sample 87. Surface of a 300 nm slice sample rnicrotomed ai room temperature
F i A-1%. SEM image of sample 88. Surfâce of a 300 nm slice sample microtomed at room temperature
Figure A-127. SEM image of sample 88. Surface of a 300 nm slice sarnple microtomed ar roorn t e m m
F i e A-1243. SEM image of sarnple 88. Surface of a 300 nm slice sample microtomd at room temperature
Figure A-129. SEM image of sample 89. Surface of a 300 nrn slice sample microtomed at room temperature
F'Ïgure A-130. SEM image of sample 89. Surface of a 300 nm slice sample microtomeû at room temperature
Figure A-131. SEM image of sample 89. Surface of a 300 nrn slice sample rnicrotomed at m m temperature
Figure A-132. SEM image of sample 89. Surfiace of a 300 nm slice sample rnicrotomed ai m m temperanire
Figure A-133. SEM image of sample 59. Surface of a 300 nm siice sample microtomed at room temperature
F i n A-134. SEM image of sample 59. Surface of a 300 m siice sarnple micmtomed at m m temperanire
Figure A-135. SEM image of sample 59. Surface of a 300 nrn slice sample microtomed at m m temperature
Figure A-136. SEM image of sarnple 58. Surface of a 300 nm slice sample microtomed at room tempemure
Figure A-137. SEM image of sample 58. Surface of a 300 nm slice sample microtomed at room temperahm
Figure A-138. SEM image of sample 58. Surface of a 300 nm slice sample microtorned at room temperature
Figure A-139. SEM image of sample 58. Surface of a 300 nm slice sample microtomed at room temperature
F i A-140 SEM image of sample 58. Surfâce of a 300 nm slice sample microtomed at room tempefanire
Figure A-141 SEM image of sample 57. Surface of a 300 nm slice sample microtomed at room temperature
Figure A-142 SEM image of sarnple 56. Surface of a 300 mn slice sample micmtomed at room temperature
Figure A-143 SEM image of sample 55. Surface of a 300 nm s k e sample microtomed at m m temperature
Figure A-144 SEM image of sample 49. Surface of a 300 mn slice sample microtomed at room temperature
Figure A-145 SEM image of sample 48. Figure A-146 SEM image of sample 47. Surface of a 300 nm slice smple Surface of a 300 nm slice sample microtomed at room temperature microtomed at m m temperature
Figure A-147 SEM image of sample 47. Figure A-l4û SEM image of sample 46. Surface of a 300 nm slice sample Surface of a 300 nm siice sample rnicrotomed at room temperature microtomeci at room ternpemiwe
Figure A-149 SEM image of sample 45. Surface of a 300 nm slice sample microtomed at room temperanue
F i A-150 SEM image of sample 35. Surface of a 300 nm slice sample microtomed at m m temperafure
Figure A-151 SEM image of sample 85. Surface of blocks microtomed at room tem perature. Oniy decornposition reveals the f e a m on microtomed flat surfaces.
F i A-152 SEM image of sarnple 87. Surfixe of a block rnicmtmed at m m temperature. Only decomposition r e v d the fea~res on micmtomed flat surfaces.
Figure A-153 ISTM image of sample 89. Surface of a block of sample microtomed at room temperature. XY = 9000 x 9000 nrn. Z range = 127 nm.
Figure A-154 ISTM image of sample 88. Surfâce of a block of sample microtomed at room temperature. XY = 9000 x 9000 nrn. Z range = 297 nm
Figure A-155 ISTM image of sample 87. Surface of a block of sample micfotomed at room temperature. XY = 9000 x 9000 nrn. Z range = 223 nm
F i A-156 ISTM image of sample 86. Surface of a block of sample microtomed at room temperame. XY = 9000 x 9000 m. Z range = 321 nm
Figure A-157 ISTM image of sample 85. Surface of a block of sample micfotomed at room temperature. XY = 9000 x 9000 nm, Z range = 299 nm
F i n A-158 ISTM image of sarnpie 84. Surface of a block of sarnple microtomed at room ternperanire. XY = 9000 x 9000 m, Z range = 367 nm
Figure A-159 ISTM image of sample 83. Surface of a block of sample mictotomed at room temperature. XY = 9000 x 9000 nm. Z range = 206 nm
F i i A-1éû ISTM image of sampie 82. Surface of a Mock of sample microtomed at room temperature. XY = 9000 x 9000 m. Z rame = 234 nm
Figwe A-161 ISTM image of sample 81. Surface of a block of sample microtomed a: room temperature. XY = 9000 x 9000 nm. Z range = 245 nm
Fit A-162 ISTM image of sample 89. Surface of a block of sample microtomed at m m temperanire. XY = 4500x4500 nm, Z range = 70 nm
Figure A-163 ISTM image of simple 88. Surface of a block of sample microtomd at room temperature. XY = 4500x4500 nm. Z range = 176 nm
Frgure A-lé4 ISTM image of sample 87. Surfze of a Mock of sample miaotomed at room temperature. XY = 4500x4500 nrn. Z range = 270 nm
figure A-lé5 ISTM image of sample 86. F i A-1éé ISTM image of sample 85. Surface of a block of sample microtomed Surface of a block of sample microtomeci at room temperature. XY = 4500x4500 at m m temperature. XY = 4500x4500 m. Z range = 248 nm nm. Z range = 26 1 nrn
Figure A-167 ISTM image of sarnple 84. Surface of a block of sample microtomed at room temperature. XY = 4500x4500 nm. Z range = 289 nm
Fwn A-168 ISTM image of sample 83. Surface of a Mock of sample microtomed at m m temperature. XY = 4500x4500 nrn. Z range = 168 nm
Figure A-169 ISTM image of sample 82. Surface of a block of sample micf01Omed at m m temperanite. XY = 4500x4500 nrn, Z range = 278 m
Fwre A-170 ISTM image of sample 81. Surface of a Moçk of sample microîomed at m m temperature. XY = 4500x4500 nm. Z range = 289 nm
Figure A-171 ISTM image of sample 59. Surface of a block of sample micfotomed at rmm temperature. XY = 4500x4500 nm. Z range = 136 nm
Fiin A-172 ISTM image of sample 58. Surfxe of a block of sample microtomed ai room temperature. XY = 4500x4500 nm. Z range = 145 nrn
Figure A-173 ISTM image of sample 57. Surface of a block of sample microtomed at room temperature. XY = 4500x4500 nm, Z range = 181 nrn
Figure A-174 ISTM image of sample 56. Surface of a Mock of sarnple microtomed at room temperature. XY = 4500x4500 nm, Z range = 148 nm
Figure A-175 ISTM image of sample 55. Surface of a block of sample rnicrotomed at m m tempefanire. XY = 4500x4500 nm. Z range = 82 nm
F~ure A-176 ISTM image of sample 54. Surface of a biock of sample microtomed at m m temperature. XY = 4500x4500 nm. Z range = 105 nm
Figure A-177 ISTM image of sample 53. F i ,40178 ISTM image of sample 52. Surface of a bloçk of sample mimtomed Surface of a Mock of sample microtomed at room temperature. XY = 4500x4500 at mom temperaiure. XY = 4500x4500 nrn. Z range = % nm nm. Z range = 132 nm
Figure A-179 ISTM image of simple 45. F w r e A-180 ISTM image of sample 46. Surface of a block of sample microtomed Surface of a block of simple microiomed at room temperature. XY = 4500x4500 at m m temperature. XY = 4500x4500 nrn. Z range = f 1 6 nm nm, Z range = 65 nm
F i e A-181 ISTM image of sample 47. Surface of a block of sample microtomed at room temperature. XY = 4500x4500 nm. Z range = 95nm
Figure A-183 ISTbf h g e of smple 36. Surface of a block of simple microtomed
FhWe A-182 ISTM image of sample 35. Surface of a bIock of ample micraomed
,t ra>m temperature. XY = 4500~45m ai m m temperame. XY = 4500x4500 nrn, Z range = 109 nm Z range = 126 run
Figure A-185 STM image of sample 89. F i n A-186 STM image of sample 88. Surface of a block of sample micrutmed at Surface of a Mock of sarnple microtomed roorn temperature. XY = 9000 x 9000 nm. at rom ternperaiure. XY = 9000 x 9000 Z range = 195 nm nrn. Z range = nm
Figure A-187 STM image of sample 87. F q u n A-188 STM image of sarnple 86. Surface of a block of sample miaotomed Surface of a block of sample mictolomed at at room temperature. XY = 9000 x 9000 room temperature. XY = 9000 x 9000 nrn, nrn, Z range =414 nrn Z range = 537 nm
Figure A-189 STM image of sample 85. Fwre A-190 STM image of sample M. Surface of a block of sample microtomed at Surfaçe of a block of sample microtomed m m temperature. XY = 9000 x 9000 nm. at room temperature. XY = 9000 x 9000 Z range = 379 nm nm. Z range=417 nm
Figure A-191 STM image of sarnple 83. Figure A-192 STM image of sample 82. Surface of a block of sample microtomed at Surface of a block of sample microtmed room temperature. XY = 9000 x 9000 nm. at room temperature. XY = 9000 x 9000 Z range = 4 17 nrn nm, Z range = 459 nm
Figure A-193 STM image of sarnple 81. F i A-194 STM image of sample 89. Surface of a block of sample m i c m e d at Surface of a block of sample rnicrotomed roorn temperature. XY = 9000 x 9000 nm, at room temperature. XY = 4500 x 4500 Z m g e = 459 nm nm, Z range = 444 nm
F i r e A-195 STM image of sample 88. F"igun A-1% STM image of sample 87. Surface of a block of sampk miçrotomed at Surfxe of a block of sarnple microtomed room temperanite. XY = 4500 x 4500 run, at mom temperature. XY = 4500 x 4500 Z range = 444 nrn Horizontal effects are nm. Z range = 404 nm caused by vibration of knife at c u b g
Figure A-197 STM image of satnple 86. Fin A-198 STM image of sample 8.5. Surface of a block of sample niIcroiomed at Surface of a block of sample microtomed room temperature. XY = 4500 x 4500 nm, at room temperature. XY = 4500 x 4500 Z range = 488 nm nm, Z range = 4454 nm
Figure A-199 STM image of sample 84. F i A-ZOO STM image of sample 83. Surface of a block of sarnpk microtomed at Surface of a block of sample micmtomed room temperature. XY = 4500 x 4500 nm, at room temperature. XY = 4500 x 4500 Z range = 379 nm nm. Z range=420m
Figure A-201 STM image of sample 82. F- A-Zû2 STM image of sample 81.
Surface of a block of sarnple micmomed at Surface of a Mock of sample microtomed room temperature. XY = 4500 x 4500 nm. at room tempature. XY = 4500 x 4500
Z range = 417 nm nm, 2 range = 4380 nm
Figure A-203 STM image of sample 59. Fiin A-2û4 STM image of sarnple 58. Surface of a block of sampte microromed at Surface of a block of sample micrwtomed rmm temperature. XY = 4500 x 4500 m. at niom temperaîure. XY = 4500 x 4500 Z range = 379 nm nm. Z range = 314 nm
Fwre A-= STM hage of sample 57. F w n A-2Od STM image of sample 56. Surface of a block of sample microtomed at Surface of a block of sample microtomed rom tempetanire. XY = 4500 x 4500 m. at room temperanire. XY = 4500 x 4500 Z range = 404 nrn m. Z range = 306 nm
Figure A-207 STM image of sample 55. Figrin A-208 STM image of sample 54. Surface of a block of sarnpte microtomed at Surfâce of a block of sample microtomed m m temperature. XY = 4S00 x 4500 nrn. at room temperanire. XY = 4500 x 4500 Z range = 380 nrn nrn. Z range = 380 nm
Figure A-209 STM image of sample 53. Fwre A-210 STM image of sunple 52
Surface of a block of sample microtomed at Surface of a biock of sample mimtomed room temperature. XY = 4500 x 4500 nm. at m m temperanise. XY = 4500 x 4500
Z range = 3380 nm nm. Z range= 381 nm
Fgure A-211 STM image of sample 51. Figure A-212 STM image of sample 44.
Surface of a block of sample microtomed at Swface of a block of sarnple microtomed room t e m m r e . XY = 4500 x 4500 nm. at m m temperature. XY = 4500 x 4500
- -
Z range = 214 nm nrn, Z range = 254 nm
Figure A-213 STM image of sample 45. Figure A-214 STM image of sample 46. Surface of a block of sample micrutomed at Surfafe of a block of sample microtomed room temperature. XY = 4500 x 4500 nm, at room temperature. XY = 4500 x 4500 Z range = 177 nrn nm. Z range = nm
Frgure A-215 STM image of sample 47. Figure A-216 STM image of sample 35. Surface of a block of sample microtomed at Surface of a block of sample microtomed room temperature. XY = 4500 x 4500 m. at m m temperature. XY = 4500 x 4500 Z range = nrn nm, Zrange= 218nrn
Figure A-217 STM image of sarnple 36. Fiire A-218 STM image of sample 89. Surface of a block of sample microtomed at Same scan as Fig. A-185. image analysis room tempemure. XY = 4500 x 4500 m. gives the counter lines. Z range = 112 nrn
Figure A-219 STM image of sample 89. Same scan as Fig. A-185. lrnage analysis gives t h e dimensional view of Lhe surface.
Fwre A320 STM image of sample 85. Sarne scan as Fig . A- 189. Image analysis gives three dimensional view of the surface
Figure A-221 STM image of sarnple 89. Figure A-222 STM image of sample 89. Same scan as Fig. A- 194. image analysis Same scan as Fig. A- 194. image analysis gives three' dimensional. line plot of ttie gives rhree dimensional view of the Sclzface Surface
Figure A-223 STM image of sample 89. Same scan as Fig. A-194. Image analysis gives a cross section with uiickness of I nm.
Figure A-224.
Correlation of morphology of the separated phases and the composition of the samples. The images are arranged in the table which columns represent the volume fiaction of the copolyrner in the biend (Q). and rows re!present the volume fraction of styme in the copolymer (x). These images were taken by i'YanoScope CI STM. For aii of the samples in this table,, the scan size is XV = 9000 x 9000 am.
Copol ymer composition
Figure A-224. Continued.
Correlation of morphology of the separated phases and the composition of the samples. The images are arranged m the table which colurnns represent the volume fraction of the copolymer in the blend (@), and rows represent the volume fiaction of styrene in the copolymer (x). niese images were taken by NanoScope II STM. For a i i of the samples in ihis table.. the scan size is XY = 9000 x 9000 nm.
Figure A-225.
Correlation of morphology of ihe separated phases and the composition of the samples. The images are arrangeci in the table which c o l m represent the volume h t i o n of the copolyrner in the blend (@). and rows repesent the volume fraction of styrene in the copolymer (x). These images were taken by NanoScope II STM. For al1 of the samples in this table.. the scan size is XY = 4500 x 4500 am,
Copoiymer composition
Figure A-225. Continued.
Correlation of morphology of the separated phases and the composition of the samples. The images are arranged in the table which columns represent the volume fraçtion of the copolymer in the blend (Q), and mws represeni the volume fraction of styrene in the copolymer (x). These images were taken by NanoScope II STM. For al1 of the samples in îhis table., the scan size is XY = 4500 x 4500 nm.
9.2. Graphs
Figure A-226. Histogram of particle size distribution for sample 89. Data was oblained from the darker spots in the Fig. A-2 1 (fracture SEM). Ave.=349 nrn.
Particle Size (nm)
Fmre A-227. Histojpn of particle size distribution for sample 89. Sarne as Fig. A-226, but for lighter spots. Ave.=265 nm.
Particle Size (nm) Particl Size
Figure A-228. Histogram of particle size Figure A-229. Histogram of paràcle size distribution for sample 89. Surn of disaibution for sample 89. Data was histograms of Fig. A-226 and A-227. obtained from sum of 7 images. (fracture.
SEM)
Particle Site (nm)
Figure A-230. Histogram of particle size distribution for sarnple 89. Same as the histograrn in Fig. A-229. but with wlurnn bars.
O ~ ~ - ~ ~ N ~ ~ ~ O ~ ~ ~ ~ U ) N ~ W ~ O ~ W - W ~ N ~ > < O O O , 0 ~ ~ ~ O - m ~ b ~ O N ~ ~ h 9 0 N t ~ h Q > O N t V > h 0 > ~
e c - t - - w N a N N m m m m m O m w w W * * v V >
Panicle size (nm)
Figure A-232. Histogram of particle size distribution for simple 59. Data was obtained from Fig. A-133 (slice. SEM). Ave.=87 nm.
a N m Q c * h O e w m N V > Q r w b O m a - ~ - 0 a m w a m * Q N 9 m a e a N * Q , N -
r - r O J N O J m m m * ~ t m m m ~ 9 Q h +
Particle Size (nrn)
Fïre A-231. Histogam of particle size distribution for sample 89. Same as the histogram in Fig. A-230. but srnoothened.
O ~ N ~ W ~ ~ ~ W ~ ~ ~ ~ ~ W ~ ~ ~ Q Q ~ O T ~ ~ W V > < O ~ ~ Q > O - ~ ~ w m @ ~ ~ ~ C N O I W ~ b W ~ O N C ) * V > w h ~ ~ o ~ r >
- - - - - - - - -aNOJNamNNNmmm
Particle Size (nmj
Figure A-233. Histograrn of particle size distribution for sample 59. Data was obtauied by surnming the data h m 4 different images- Ave.=99 nrn.
Particle Size (nm)
Figure A-234. Histogram of particle size distribution for sarnple 58. Data was obtained fron Fig. A- 139.(slice. SEM). Ave.=151 nm.
F i r e A-235. Histogram of particle size dismbution for sample 58. Data was obtauied by summing the data h m 5 different images. Ave.= 158 nrn.
Particle Size (nm) Particle Size (nm)
figure A-236. Histogram of particle size F i u n A-237. Histogmm of particle size distribution for sample 89. Data was distribution f a sample 89. Data was obtained from Fig. A-129 (slice. SEM). obiained by sumrning the data From 3 Ave.=353 nrn. different images. Ave.=266 nm.
Particle size (nm) Particle Site (nm)
Figure A-238. Histogram of particle size Figure A-239. Wistogram of particle size distribution for sample 88. Data was distribution fa sample 88. Data was obtained from Fig. A-126 (slice. SEM). obmined by summing the &ta from 4
Ave.=442 nm. different images. Ave.=437 nrn.
Particle Site (nm) Particle Site (nm)
Figure A-240. Histograrn of particle size Figure A-241. Histogram of particle size distribution for sample 58. Daia was distribution f a sample 58. Data was obtained from Fig. A-204 (STM). obiained by summing the data from 2 Ave.=184 nm. different images. Ave.= 1% 1 nm.
Particle Size (nm)
Figure A-242. Histopam of particle ske distribution size for sample 59. Data w a ~ obtained from Fig. A-203 (STM). Ave.= 150 nm.
Particle Size (nm)
F i e A-243. Histogram of part..de size distribution fa sample 59. Data was obîaîned by summing the data m m 3 different images, Ave.=154 m.
Particle Size (nm)
315 630 945 1260
Particle Size (nm)
.Figure A-244. Histograrn of particle size Figure A-245. Histogram of particle size disiribution for sarnple 88. Data was disiribution for sample 88. Data was obtained From Fig . A- 186. Ave.=549 nm. obtained by summing the data from 3
different images. Ave.=5 1 1 m.
Particle Size (nm)
.Figure A-246. Histogram of particle size distribution for sample 89. Data was obtained from Fig. A-185 (STM). Ave.=386 nm.
Particle Size of PMMA (nm)
- Distance of Paru'cles
Volume Fraction of Copolymer
Figure A-24û. Histogram of particle size and distance distribution f a the samples of series 8 copolymer. Data was obtained ûum the images in Fig. A-225.
Particle Size (nm)
Figure A-247. Histopam of particle size distribution for sample 89. Data was obtained by sununing the data h m 3 different images. Ave. = 4 19 nm.
Particle Size of PMMA(nm)
Distance of Particles (nm)
O 0.1 0.2 0 . 3 0.4 0 .5 0.6 0.7 0 .8 0.9 1
Volume Fraction of Copolymer
Fwre A-249. Kstogram of particle size and distance distribution f a the samples of series 5 copolymer. Data was obrained h m the images in Fig. A-225.
PMMA blend Transparency
Transmit tance (2) 650 nm
Figun A-250. Transparency of different blend samples for monochrome light with M 5 0 nm.
O 0.25 0.6 0.75 1
Volume fraction of copolymer (-1
PMMA blend Transparency - 60/40 blend
Transmit tance (%) 100
Fqure A-251. Transparency of series 4 blend samples (Le. of copoIymer 40:60) for light with different wavelengths
O 0.25 0.5 0.75 1
Volume fraction of copolymer (-)
8.00 -f------? , 1 1 l
80.0 90 .O 100.0 110.0 120 .O 130.0
2-run Temeratma [*Cl - .- Figure A-252. DSC trace of the ~ample 30 (pure PMMA).
Second run Tamperaturs ('Cl - +-
Figure A-253. DSC trace of the ~ample 810 (pure 80:20 copolym
