Orientation and phase behavior of block copolymers in external electric fields [Elektronische Ressource] / vorgelegt von Kristin Schmidt

Informations

• Publié par: universitat_bayreuth
• Publié le: 01 janvier 2007
• Nombre de lectures: 22
• Langue: Deutsch
• Poids de l'ouvrage: 8 Mo

Extrait

Orientation and Phase Behavior of
Block Copolymers in External
Electric Fields
DISSERTATION
zur Erlangung des akademischen Grades eines
Doktors der Naturwissenschaften
- Dr. rer. nat. -
der Fakult¨at Biologie, Chemie und Geowissenschaften
der Universit¨at Bayreuth
vorgelegt von
Kristin Schmidt
geboren in Bad Salzungen
Bayreuth, 2007Vollst¨andiger Abdruck der von der Fakultat¨ Biologie, Chemie und
Geowissenschaften der Universit¨at Bayreuth genehmigten Dissertation zur
Erlangung des akademischen Grades Doktor der Naturwissenschaften
(Dr. rer. nat.).
Die vorliegende Arbeit wurde in der Zeit von November 2003 bis Juni 2007 am
Lehrstuhl fur¨ Physikalische Chemie der Universit¨at Bayreuth in der Arbeitsgruppe
von Herrn Prof. Dr. Georg Krausch und Herrn Prof. Dr. Alexander Bo¨ker
angefertigt.
Die Arbeit wurde eingereicht am: 14. Juni 2007
Das Kolloquium fand statt am: 14. November 2007
Der Prufungsaussc¨ huss bestand aus:
Prof. Dr. Alexander B¨oker (Erstgutachter)
Prof. Dr. Axel Muller¨ (Zweitgutachter)
Prof. Dr. Helmut Alt (Vorsitzender)
Prof. Dr. Thomas HellwegMeiner Familie
Jede L¨osung eines Problems ist ein neues Problem.
Johann Wolfgang von Goethe.Contents
1 Introduction 1
1.1 Microphase Separation of Block Copolymers . . . . . . . . . . . . . . 2
1.1.1 Morphologies in Diblock Copolymers . . . . . . . . . . . . . . 3
1.1.2 Theoretical Models for the Microphase Separation . . . . . . . 4
1.1.3 Block Copolymers and Solvents . . . . . . . . . . . . . . . . . 9
1.2 Electric Field Induced Alignment of Block Copolymers . . . . . . . . 10
1.2.1 Electrothermodynamics . . . . . . . . . . . . . . . . . . . . . 10
1.2.2 Overview of Recent Studies . . . . . . . . . . . . . . . . . . . 14
1.3 Structure of this Thesis . . . . . . . . . . . . . . . . . . . . . . . . . . 19
2 Methods 21
2.1 Synthesis. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 21
2.1.1 Anionic Polymerization . . . . . . . . . . . . . . . . . . . . . . 21
2.1.2 Gel Permeation Chromatography . . . . . . . . . . . . . . . . 24
2.1.3 NMR Spectroscopy . . . . . . . . . . . . . . . . . . . . . . . . 25
2.2 Small-Angle X-Ray Scattering . . . . . . . . . . . . . . . . . . . . . . 25
2.2.1 Basics of Scattering . . . . . . . . . . . . . . . . . . . . . . . . 26
2.2.2 Diffraction by Crystals . . . . . . . . . . . . . . . . . . . . . . 27
2.2.3 Scattering on Microphase Separated Block Copolymers . . . . 29
2.2.4 Experimental Setup . . . . . . . . . . . . . . . . . . . . . . . . 32
2.2.5 Data Reduction . . . . . . . . . . . . . . . . . . . . . . . . . . 35
2.3 Simulation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 37
3 Experimental Section 43
3.1 Synthesis. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 43
3.2 Sample Preparation . . . . . . . . . . . . . . . . . . . . . . . . . . . . 45
3.3 SAXS Setup . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 463.4 Data Evaluation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 47
4 Influence of Initial Order on the Microscopic Mechanism of Alignment 51
4.1 Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 51
4.2 Materials . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 53
4.3 Deconvolution of Reorientation Process . . . . . . . . . . . . . . . . . 53
4.4 Results and Discussion . . . . . . . . . . . . . . . . . . . . . . . . . . 55
4.4.1 Results from in-situ SAXS Measurements . . . . . . . . . . . . 55
4.4.2 Computer Simulations . . . . . . . . . . . . . . . . . . . . . . 59
4.4.3 Comparison of Experiments with Computer Simulation . . . . 61
4.5 Conclusion . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 65
5 On the Physical Origin of Block Copolymer Alignment 67
5.1 Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 67
5.2 Materials . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 68
5.3 Results and Discussion . . . . . . . . . . . . . . . . . . . . . . . . . . 69
82 1005.3.1 Comparison of S H M and S M . . . . . . . . . . . 6947 10 43 49 51
5.3.2 Scaling Behavior . . . . . . . . . . . . . . . . . . . . . . . . . 71
5.3.3 Computer Simulations . . . . . . . . . . . . . . . . . . . . . . 73
5.3.4 Estimation of the Threshold Electric Fields. . . . . . . . . . . 76
5.3.5 Kinetics in AC Electric Fields . . . . . . . . . . . . . . . . . . 77
5.4 Conclusion . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 79
6 Electric Field Induced Order-Order-Transitions 81
6.1 Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 81
6.2 Materials . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 83
6.3 Results and Discussion . . . . . . . . . . . . . . . . . . . . . . . . . . 83
6.3.1 Phase Diagram without Electric Field . . . . . . . . . . . . . . 83
6.3.2 Alignment of Lamellae . . . . . . . . . . . . . . . . . . . . . . 87
6.3.3 Effect of the Electric Field on the HPL Phase . . . . . . . . . 88
6.3.4 Effect of the Field on the Gyroid Phase . . . . . . . . 90
6.3.5 Alignment of Cylinders . . . . . . . . . . . . . . . . . . . . . . 93
6.4 Conclusion . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 95
7 Electric Field Induced Changes in the Periodicity of Block Copolymer
Microdomains 97
7.1 Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 977.2 Materials . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 98
7.3 Results and Discussion . . . . . . . . . . . . . . . . . . . . . . . . . . 99
7.3.1 Effect of an Electric Field on the Polymer Chains . . . . . . . 99
7.3.2 Influence of Different Physical Parameters . . . . . . . . . . . 101
7.3.3 Kinetic Measurements . . . . . . . . . . . . . . . . . . . . . . 104
7.3.4 Influence on a Cylindrical Block Copolymer . . . . . . . . . . 106
7.3.5 Methacrylate Based Systems . . . . . . . . . . . . . . . . . . . 107
7.3.6 Effect on PS-b-PVP . . . . . . . . . . . . . . . . . . . . . . . 109
7.4 Conclusion . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 110
8 Summary/Zusammenfassung 111
9 Bibliography 119
10 List of Publications 133Introduction
In this thesis a discussion of electric field induced effects on block copolymer mi-
crodomains is presented. The mechanism and kinetics as well as the driving forces
of the alignment process are investigated. Furthermore, the influence of an electric
field on the phase behavior is studied.
Many applications of ordered mesophases in soft materials have emerged dur-
ing the recent years. Block copolymers have gained considerable potential for
nanotechnological applications, such as nanostructured networks and membranes,
nanoparticletemplates,andhigh-densitydatastoragemedia[Has97,Bat90a,Bat99,
Urb00]. Block copolymers composed of incompatible components self-assemble
into microphase separated domains and, hence lead to well-ordered structures on
the mesoscale. However, in the absence of external fields, typically an isotropic
grain structure is obtained, which is characterized by a random distribution of mi-
crodomain orientations. In view of potential applications the control of long-range
orderandtheremovalofdefectsremainsacrucialissue. Therefore, numerousroutes
havebeendevisedtoalignthemicrodomainsoverlargescalesbyuseofexternalfields
such as shear fields [Kel70, Win93, Alb94, Che97], temperature gradients [Has99]
and electrical fields (see section 1.2.2).
Both lamellar and cylindrical microdomain structures were oriented macroscopi-
cally by virtue of a DC electric field. Experiments in the melt, however, are limited
by the high viscosities typical for high molecular weight copolymers or copolymers
of more complex architectures. These limitations can be circumvented by using
concentrated block copolymer solutions in nonselective solvents [B¨ok02b, B¨ok03b].
While the aligning effect of DC electric fields on non-cubic block copolymer mi-
crophases is indisputable, its physical origin is still somewhat contentious. Two
potential driving forces are being discussed. A commonly used argument is based
on the fact that the dielectric contrast between the copolymer blocks will lead to
a minimum in electrostatic free energy whenever the interfaces between the two di-
electrics are oriented parallel to the electric field vector [Amu93]. As an alternative
1Introduction
driving force the potential existence of mobile ions has been discussed, which may
contributetothereorientationprocessviathecreationofaneffectivepolarizationof
the anisotropic block copolymer structure [Tso03b]. While the free energy penalty
canbeeliminatedbyreorientationoflamellaeandcylinders, itcannotbeeliminated
incubicphases,suchasthegyroidorsphericalphase,butonlyreducedbydistorting
the phase.
In the first part of this thesis experiments examining the mechanism and kinetics
of the alignment of lamellar forming diblock copolymer solutions are presented.
The influence of the degree of initial order on the microscopic route towards domain
alignmentisstudied. Furthermore,toclarifythedrivingforceofreorientation,afirst
quantitative study of the reorientation kinetics of various model block copolymers
exposed to an electric field is presented. Moreover, first kinetic experiments in hig