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In-situ Investigation of the shear-induced alignment of Diblock Copolymer Melts using Rheo-SAXS, Rheo-Dielectric and FT-Rheology [Elektronische Ressource] / Thomas Meins

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216 pages
In-situ Investigation of the shear-induced alignment of Diblock Copolymer Melts using Rheo-SAXS, Rheo-Dielectric and FT-Rheology Zur Erlangung des akademischen Grades eines DOKTORS DER NATURWISSENSCHAFTEN (Dr. rer. nat.) Fakultät für Chemie und Biowissenschaften Karlsruher Institut für Technologie (KIT) – Universitätsbereich Vorgelegte DISSERTATION Von Thomas Meins Aus Bayreuth Dekan: Prof. Dr. S. Bräse Referent: Prof. Dr. M. Wilhelm Korreferent: Prof. Dr. C. Barner-Kowollik Tag der mündlichen Prüfung: 12.07.2011 Die vorliegende Arbeit wurde von November 2007 bis Juni 2011 unter der Betreuung von Herrn Pof. Dr. Manfred Wilhelm am Karlsruher Institut für Technologie (KIT) - Universitätsbereich angefertigt. „Geistreich sein heißt, sich leicht verständlich zu machen, ohne deutlich zu werden “-Jean Anouilh Für meine Familie Duygu, Papatya, … Contents 1. Introduction ......................................................................................................... 1 2. Theory ................. 5 2.1. Principles in Rheology ........................................................................................... 5 2.1.1. Viscosity and elasticity .............. 6 2.1.2. Phenomenological models ....................................................................... 8 2.1.3. Oscillatory deformation ........... 11 2.1.4. Time Temperature Superposition (TTS) .......
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In-situ Investigation of the shear-induced alignment of
Diblock Copolymer Melts using Rheo-SAXS, Rheo-
Dielectric and FT-Rheology




Zur Erlangung des akademischen Grades eines
DOKTORS DER NATURWISSENSCHAFTEN
(Dr. rer. nat.)
Fakultät für Chemie und Biowissenschaften
Karlsruher Institut für Technologie (KIT) – Universitätsbereich

Vorgelegte

DISSERTATION

Von

Thomas Meins

Aus

Bayreuth



Dekan: Prof. Dr. S. Bräse
Referent: Prof. Dr. M. Wilhelm
Korreferent: Prof. Dr. C. Barner-Kowollik
Tag der mündlichen Prüfung: 12.07.2011


Die vorliegende Arbeit wurde von November 2007 bis Juni 2011 unter der Betreuung
von Herrn Pof. Dr. Manfred Wilhelm am Karlsruher Institut für Technologie (KIT) -
Universitätsbereich angefertigt.



„Geistreich sein heißt,
sich leicht verständlich zu machen,
ohne deutlich zu werden “
-Jean Anouilh












Für meine Familie
Duygu, Papatya, …


Contents
1. Introduction ......................................................................................................... 1
2. Theory ................. 5
2.1. Principles in Rheology ........................................................................................... 5
2.1.1. Viscosity and elasticity .............. 6
2.1.2. Phenomenological models ....................................................................... 8
2.1.3. Oscillatory deformation ........... 11
2.1.4. Time Temperature Superposition (TTS) ................................................. 15
2.1.5. The reptation model ................................................ 18
2.1.6. LAOS: Introduction to the non-linear regime .......................................... 24
2.2. Fourier Transform Rheology ............... 27
2.2.1. Basic aspects of the Fourier Transformation .......... 28
2.2.2. Principles of FT-Rheology on the stress signal ...................................... 30
2.3. Block Copolymers ............................................................................................... 32
2.3.1. Physical properties ................................................................................. 33
2.3.2. Mechanical response of diblock copolymers .......... 37
2.3.3. Symmetric diblock copolymer melts under LAOS ................................... 38
2.4. Dielectric Relaxation Spectroscopy ..................................... 41
2.4.1. Basic considerations ............................................... 42
2.4.2. Dielectric Relaxation (linear response theory) ........ 43
2.4.3. Relaxation models .................................................. 46
2.4.4. Dipole moments in polymers .................................................................. 48
2.5. Small angle X-ray scattering ............... 51
2.5.1. Basic principles of scattering .. 51
2.5.2. The Bragg equation ................................................................................ 53
2.5.3. Structure and form factor ........ 55
2.5.4. Scattering from diblock copolymers ........................................................ 58
I

3. Experimental Methods and Setups .................................................................. 60
3.1. Anionic polymerization techniques ...... 60
3.1.1. Basic considerations ............................................................................... 60
3.1.2. Anionic synthesis of the model compounds ............ 61
3.1.3. Characterization of the model compounds ............. 64
3.2. Non-linear dynamic mechanical measurements .................................................. 69
3.2.1. Quantitative methods .............................................. 69
3.2.2. Experimental setup ................. 73
3.3. Rheo-Dielectric combination ............................................... 74
3.3.1. Recent developments / Literature review ............... 74
3.3.2. High sensitive Rheo-Dielectric combination ........... 75
3.4. In-situ Rheo-SAXS combination .......................................................................... 78
3.4.1. Recent developments / Literature review ............... 78
3.4.2. In-situ Rheo-SAXS combination ............................................................. 79
3.5. Experimental procedure ...................................................... 81
3.5.1. Sample preparation ................................................ 81
3.5.2. Sample loading and experimental procedure ......... 81
3.5.3. External SAXS measurements and sample preparation ......................... 82
3.5.4. Analysis of the 2D-SAXS pattern ............................................................ 83
4. Shear-induced orientation of PS-b-PI-13k-13k ............... 85
4.1. Literature review .................................................................................................. 85
4.2. Linear mechanical characterization ..... 87
4.3. Strain dependent alignment kinetic ..... 90
4.3.1. In-Situ Rheo-SAXS investigations .......................................................... 90
4.3.2. Online FT-Rheology investigations ....................... 100
4.3.3. Ex-situ 2D-SAXS investigations............................ 108
4.4. Summary of the strain dependence orientation process ................................... 119
4.5. Quantitative orientation kinetics ........................................ 120
II

4.6. Frequency and temperature dependent alignment kinetics ............................... 125
4.6.1. Frequency dependence ........................................................................ 125
4.6.2. Temperature dependence .... 129
4.7. Conclusion of frequency and temperature dependence .... 134
4.8. Molecular weight dependence of the shear-induced alignment ........................ 135
4.8.1. Linear mechanical characterization of PS-b-PI-17k-17k ....................... 135
4.8.2. In-situ Rheo-SAXS studies ................................................................... 136
4.8.3. Comparison of PS-b-PI-13k-13k and PS-b-PI-17k-17k ........................ 137
4.8.4. Molecular weight dependence detected by I (t) .. 141 3/1
4.9. Summary and discussion of the shear-induced alignment ................................ 143
4.9.1. Implication of the macroscopic alignment mechanism .......................... 143
4.9.2. Correlation between structural changes and mechanical response ..... 146
5. Re-orientation experiments of PS-b-PI diblock copolymers ....................... 150
6. Rheo-Dielectric studies of the shear-induced alignment ............................ 158
6.1. Dielectric relaxation spectra of PS, PI and PS-b-PI ........................................... 158
6.2. In-situ Rheo-Dielectric studies of the shear-induced alignment ........................ 162
6.2.1. Macroscopic parallel orientation ........................................................... 163
6.2.2. Macroscopic perpendicular orientation ................. 167
6.2.3. In-situ Rheo-Dielectric investigation of PS-b-PI-13k-13k ...................... 170
6.3. Summary and discussion of the in-situ Rheo-Dielectric investigations .............. 172
7. Rheo-Dielectric of gold-hybrid diblock copolymers nano-composites ...... 175
7.1. Materials and experimental procedure .............................................................. 175
7.2. Static dielectric studies ...................................................... 178
7.3. In-situ Rheo-Dielectric investigations ................................ 183
7.4. Summary and discussion of the Rheo-Dielectric investigations ........................ 187
8. Concluding Remarks ...................................................................................... 189
9. Experimental Part ............................ 192
9.1. High vacuum polymerization techniques ........................................................... 192
III

9.2. Purification of solvents and monomers ............................................................. 192
9.3. Synthesis of the homopolymers and diblock copolymers .................................. 194
10. Bibliography .................................................................... 197


IV


1. Introduction
The term polymer, derived from ancient Greek πολύς (polus “many, much”) and
μέρος (meros “part”), defines a class of materials which consist of several (hundreds
to thousands) chemical repeating units. Most of the polymer materials used
frequently in our daily life are synthesized form chemical substances, the so called
monomers. The monomers originate from natural recourses mainly from fossil
resources like crude oil. Common monomers are carbon compounds which obey
chemical reactive functionalities for instance double bounds like styrene, ethylene,
propylene or isoprene.
There are numerous polymerization methods, with different weightings for
industrial and scientific applications. The prevalent techniques applied for large scale
processing are the free radical polymerization, polycondensation respectively
addition polymerization for the production of polyester and polyamides respectively
polyurethanes and the coordinative polymerization using organo metals as catalysts
1for the synthesis of polyethylene and polypropylene . The focus of recent scientific
efforts is based on the development and improvement of controlled polymerization
2-4techniques such as the Reversible Addition-Fragmentation chain Transfer (RAFT) ,
5, 6nitroxide-mediated polymerization (NMP) , Atom Transfer Radical Polymerization
7-9 10-13 14, 15(ATRP) or the anionic respectively cationic polymerization. These so called
“living” polymerization techniques facilitate the synthesis of well defined complex
macromolecular architectures. Depending on the adopted monomer, polymerization
method and experimental conditions a large variety of chemical and especially
mechanical properties can be achieved. These macromolecular materials have been
rapidly substituting or enhancing classical materials as steel, alumina, concrete or
mineral glass.
Due to the extraordinary range of polymer properties, they are suitable for a large
variety of industrial applications such as packaging, construction or health care.
Polymers possess low densities combined with excellent mechanical properties as
well as large scale processing capabilities with a minor cost of production. These are
only some of their key advantages of polymer materials. The ubiquitous roles in
everyday life range from familiar synthetic plastics, degradable biopolymers to phase
separated systems with various microstructures on a nanometer length scale. From
1

Fig. 1 it can be seen that since the early 1950 the worldwide production of polymers
has increased from approximately 1.5 million tons to more than 240 million tons in
162010 and this increase seems to be kept on .


Fig. 1 World production per year of polymers.©EuropePlastics

To serve the increasing demand of polymer materials as well as to develop
processes to produce advanced functional materials, it is from major importance to
understand and control the mechanical properties of the polymer materials. During
the modeling step the polymer melts are exposed to strong mechanical fields,
17-19affecting the melt flow behavior during processing which affect the quality of the
final product. Furthermore, hierarchical structured materials such as block
20, 21copolymers are able to macroscopically align under mechanical stimulus . A
precise understanding of these processes enables the production of new functional
materials with tailored properties. Therefore the necessity derives, to precisely
characterize and quantify the mechanical properties of the polymer materials, utilizing
rheological techniques.
Rheology is the study of the flow of matter and is adapted to substances which
22have a complex molecular structure, as polymers . The flow of polymer melts cannot
be characterized by a single value of viscosity respectively elasticity. Moreover, the
mechanical properties are a complex function depending on various factors such as
temperature, mechanical deformation or the applied shear profile as well as
molecular parameters like the chain architecture and the degree of polymerization.
2

Polymers obey both, viscous and elastic characteristics, therefore defined
23viscoelastic materials . Systems which obey additional phase separation, such as
block copolymers, show even more complex flow behavior, attributed to the
numerous different morphologies and complex structures.
Block copolymers consist of two or more different building blocks covalently bond
to each other. Driven by thermodynamic effects, these systems may undergo phase
separation into self assembled microstructures. These microstructures exhibit various
morphologies depending on the chemical composition of the different blocks,
24-26temperature and the volume fraction of the blocks . It has been proven by Koppi
27et. al. , that block copolymer melts, containing randomly ordered anisotropic
domains on a sub-micrometer scale, can be shear-induced aligned to an ordered
structure with long range periodicity. This orientation process is of great scientific and
industrial interest, as for almost all advanced applications involving block copolymers,
such as ionic or photonic conductors or functional membranes, the hierarchically
28structured materials have to become macroscopic anisotropic .
In this thesis the flow behavior of complex fluids, with a particular focus on the
non-linear regime, is investigated, utilizing sensitive and unique in-situ rheological
combinations. For the mechanical analysis of complex fluids, several different
23, 29techniques can be utilized . These cover a vast number of shear cell geometries
and test setups from steady shear over transient to dynamic measurements.
For the macroscopic orientation of symmetric block copolymers, large amplitude
oscillatory shear (LAOS) showed to be the method of choice, giving access to
different orientations of the unit normal of the lamellae with respect to the shear flow
30direction . The shear-induced alignment process causes the mechanical response of
the sample melt to become a function of time with respect to its non-linear behavior.
In the non-linear regime, during the LAOS experiment, the obtained signals consist of
higher harmonics of the applied mechanical excitation frequency ω /2π. Analyzing the 1
mechanical raw data in terms of the concept of Fourier-Transform-Rheology (FT-
31, 32Rheology) , the resulting mechanical response can be evaluated with respect to
the phase and magnitude spectra which consists of odd higher harmonics of ω /2π. 1
Utilizing FT-Rheology, the degree of mechanical non-linearity during LAOS can be
followed and quantified. In this thesis the time dependence of the intensity of the third
harmonics I(3ω ) to the fundamental I(ω ), determined from the FT-Rheology 1 1
3