Liquid Crystal Polymers: From Structures to Applications

485 Pages·1993·10.88 MB·English

by  Witold Brostow (auth.), A. A. Collyer (eds.)

LIQUID CRYSTAL POLYMERS:
FROM STRUCTURES TO APPLICATIONS
POLYMER LIQUID CRYSTAL SERIES
Edited by
D. ACIERNO
University of Salerno. Italy
W. BROSTOW
University of North Texas. USA
A.A. COLLYER
Sheffield Hal/am University, UK
Springer-sbm Archive Dordrecht
LIQUID CRYSTAL
POLYMERS:
FROM STRUCTURES TO
APPLICATIONS
Edited by
A.A. COLLYER
Division of Applied Physics,
School of Science,
Sheffield Hallam University,
UK
ELSEVIER APPLIED SCIENCE
LONDON and NEW YORK
ELSEVIER SCIENCE PUBLISHERS LTD
Crown House, Linton Road, Barking, Essex IGll 8JU, England
WITH 37 TABLES AND 203 ILLUSTRATIONS
© 1992 ELSEVIER SCIENCE PUBLISHERS LTD and THE SOCIETY OF
MATERIALS SCIENCE, JAPAN
British Library Cataloguing in Publication Data
Liquid Crystal Polymers: From Structures to Applications
I. Collyer, A.A.
547.7
ISBN 1-85166-797-0
Library of Congress Cataloging-in-Publication Data
Liquid crystal polymers: from structures to applications/edited by
A.A. Collyer
p. cm. - (Polymer liquid crystal series)
Includes bibliographical references and index.
ISBN 1-85166-797-0
1. Polymer liquid crystals. I. Collyer, A.A.
Witold, 1934- III. Series.
QD923.L568 1992 92-8744
530.4'29--dc20 CIP
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Preface
The subject of liquid crystals and their use in electronic displays and in
non-linear optical systems has become of tremendous importance during
the last decade; and the incorporation of liquid crystal units into
polymeric materials has led to a group of new materials with diverse
properties. Some of these properties have been utilized in new products
and some have yet to be used. Much published work has appeared that
deals with specific materials or particular applications, and it was felt that
a book was needed to examine and explain the underlying principles
governing the diverse properties of these liquid crystal polymers, LCPs.
The current work describes the diverse nature of LCPs, their synthesis,
characterization, properties and finally their applications. It describes the
manner in which liquid crystallinity or mesomorphism occurs in small
molecules, monomer liquid crystals and polymer liquid crystals.
Chapter 1 gives a classification of the various ways in which the meso-
gens may be connected to the polymer chains. Currently, the bulk of LCP
material is based on main chain or longitudinal LCPs for use in engineering
applications. The side chain or comb polymers are intended for use in
electronics and opto-electronic systems and as surfactants. Many other
variants and possibilities exist but their properties have not yet been fully
studied or used. In this respect it is hoped that the current work will indicate
future possibilities as well as discussing current opinion.
v
vi Preface
Chapters 2 and 3 describe methods of characterizing the mesophases.
In the former a comprehensive guide to textures is given. Chapter 4
describes the dielectric properties of LCPs. Chapters 5 to 8 inclusive deal
with comb and longitudinal LCPs, lyotropic and thermotropic. In these
chapters are discussed the syntheses, characterization, structures and
properties of these materials. Chapter 9 deals with some applications of
LCPs.
One of the important topics not covered in this text is that concerning
the effects of electric and magnetic fields on LCPs, and associated optical
effects. To cover this vast subject would be difficult in one chapter, and
the merest of introductions is given at the end of Chapter 7; readers are
urged to read the recent texts texts given at the end of this preface for a
thorough coverage of this subject. However, it is intended to cover this
area in a future volume.
'Polymer liquid crystals or liquid crystal polymers?', is a question that
baffled the editor. Several reasons for using the one or the other were put
forward by several authors. Professor Brostow, who has given a classifi-
cation of different architectures, prefers to go in a natural progression
from monomer liquid crystals to polymer liquid crystals. On the other
hand, to call the book 'Polymer Liquid Crystals' may imply that the
subject is about liquid crystals when it is really about polymers. A
majority of the contributing authors preferred the term 'liquid crystal
polymer', and as such the editor has taken refuge in the majority view.
This brief discussion then settles the aim of the book. It is intended for
workers with a knowledge of polymeric materials but scant awareness of
liquid crystallinity. It is hoped that this text will assist the reader in
understanding the latter so that an appreciation of the way in which
LCPs behave will be obtained; and, moreover, readers will be able to
appraise for themselves the possibilities unfolded by the different struc-
tures and capabilities provided by these fascinating materials, with a view
to extending their use in novel products and applications.
A.A. COLLYER
REFERENCES
1. Ciferri, A. (Ed.) LiqUid Crystallinity in Polymers: Principles and Fundamental
Properties. VCH Verlagsgesellschaft, Germany, 1991.
Preface VII
2. McArdle, C.B. (Ed.), Side Chain Liquid Crystal Polymers. Chapman and Hall,
New York, 1989.
3. Takeda, M. (Ed.), Applied Liquid Crystal Polymers. A special issue of J. Mol.
Cryst. Liq. Cryst., 1989, vi.
4. Weiss, R.A. & Ober, c.K. (Eds), Liquid-crystalline Polymers. American Chemi-
cal Society, 1990.
Contents
Preface................................................................ v
List of Contributors. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . xv
1. An Introduction to Liquid Crystallinity ............................. .
W. BROSTOW
1.1 Introduction ........... . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1
1.2 A brief history of MLCs and PLCs ............................ 2
1.3 Mesophases and their types ................................... 3
1.4 Heterogeneous composites, molecular composites and PLCs .. 4
1.5 The nature of liquid crystallinity .............................. 8
1.6 Phases of liquid crystals ....................................... 11
1.7 Classification of PLCs ......................................... 14
1.8 Molecular structures, properties and packing .................. 21
1.9 From structures to applications ............................... 23
References ..................................................... 25
2. Characterization of Mesophases.................................... 31
C. NofOL
2.1 Introduction .................................................. 31
2.2 Typical molecular structures .................................. 32
2.2.1 Low-molar-mass liquid crystals (LMMLCs) ............. 34
2.2.2 Polymers ................................................ 41
IX
x Contents
2.3 Mesophases of rod-like molecules ............................. 45
2.3.l Nematics (N) ............................................ 46
2.3.2 Cholesterics (Ch) ........................................ 48
2.3.3 Smectics (S) .............................................. 48
2.3.4 Compounds with highly polar end groups ............... 53
2.4 Textures and polymorphism of LC polymers .................. 55
2.4.l Nematic textures ........................................ 55
2.4.2 Cholesteric textures ...................................... 60
2.4.3 Smectic textures ......................................... 62
2.5 Miscibility tests ............................................... 70
2.6 X-ray diffraction patterns ...................................... 76
2.6.1 X-ray diffraction patterns for powder samples ........... 77
2.6.2 X-ray diffraction patterns for oriented samples ........... 82
2.7 Conformation of LCPs as revealed by small-angle scattering
methods .................................................... 87
References ..................................................... 91
3. NMR Studies of Thermotropic Polymers........................... 103
F. LAUPR~TRE
3.l Introduction .................................................. 103
3.2 NMR investigation of orientational conformational phenomena
in mesomorphic polymers ................................... 104
3.2.l Orientational order parameters .......................... 104
3.2.2 Principles of the NMR measurements ................... 105
3.2.3 NMR studies of orientational and conformational order in
longitudinal thermotropic polymers ................... 107
3.2.4 NMR studies of orientational and conformational order in
side chain thermotropic polymers ..................... 115
3.2.5 NMR studies of orientational and conformational order in
disco tic thermotropic polymers ........................ 122
3.3 NMR investigation of local dynamics in mesomorphic polymers 123
3.3.l Glass-liquid transition and secondary transitions ........ 123
3.3.2 Principles of the NMR experiments...................... 125
3.3.3 NMR studies of local dynamics in longitudinal liquid
crystal polymers ....................................... 127
3.3.4 NMR studies of local dynamics in side chain thermotropic
polymers .............................................. 133
3.4 NMR investigation of slow motions in mesomorphic polymers 137
3.5 Conclusions ................................................... 138
References ..................................................... 139
4. Dielectric Relaxation in Macromolecular Liquid Crystals........... 143
J.K. MOSCICKI
4.l Introduction .................................................. 143
4.2 Principles of dielectric relaxation spectroscopy ................ 144
4.3 Dielectric spectroscopy of liquid crystals ...................... 156
Contents Xl
4.3.1 Dielectric relaxation in the uniaxial phase ............... 163
4.3.2 Ferroelectric modes in chiral smectic C* phase .......... 171
4.4 Dielectric relaxation in polymers .............................. 174
4.4.1 Polymers in dilute solutions ............................. 177
4.4.2 Flexible polymers in bulk ................................ 179
4.4.3 Rod-like polymers in concentrated solutions............. 184
4.5 Dielectric spectroscopy of liquid crystal polymers ............. 187
4.5.1 Lyotropic polymers......... ............................. 191
4.5.2 Thermotropic polymers .................................. 195
References ............................................... 231
5. Lyotropic Side Chain Polymer Liquid Crystals...................... 237
P.J. HALL and G.J.T. TIDDY
5.1 Introduction .................................................. 237
5.2 Physical properties of surfactants .............................. 239
5.2.1 Dilute micellar solutions ................................. 239
5.2.2 Micelle size and shape ................................... 243
5.2.3 Liquid crystal formation of small-molecule surfactants ... 245
5.2.4 Techniques of characterization ........................... 250
5.3 Synthesis of lyotropic side chain polymer liquid crystals ....... 253
5.4 Phase behaviour of lyotropic side chain polymer liquid crystals 256
5.5 Polymerization in oriented monolayers and vesicles ........... 267
References ..................................................... 270
6. Lyotropic main chain liquid crystal polymers........................ 273
M.G. NORTHOLT and D.l. SIKKEMA
6.1 Introduction and synthetic aspects ............................ 273
6.1.1 Aromatic polyamides .................................... 274
6.1.2 Rigid-rod heterocyclic (ladder) polymers................. 276
6.2 Order in lyotropic polymer solutions .......................... 278
6.2.1 The modified Maier-Saupe mean field theory ............ 281
6.2.2 Flow behavior of lyotropic solutions .................... 286
6.2.3 Spinning of lyotropic solutions .......................... 290
6.3 Morphology of fibers and films ................................ 296
6.3.1 Chain conformation ..................................... 296
6.3.2 Results of X-ray and electron diffraction studies ......... 298
6.3.3 Characterization by optical and electron microscopy .... 305
6.3.4 Coagulation and structure formation .................... 310
6.4 Mechanical and thermal properties .................. 315
6.4.1 Elastic behavior ......................................... 318
6.4.2 Creep and stress relaxation .............................. 324
6.4.3 Strength of fibers and films .............................. 330
6.4.4 Compressive strength of fibers ........................... 334
6.4.5 Thermal properties ...................................... 337
References ............................................... 340