لایب سان

1 Liquid Crystal States of Matter 1 1.1 Liquid Crystal States 1 1.2 Appearance and Light Scattering of Liquid Crystals 4 1.3 Chemical Structure of Liquid Crystals 6 1.3.1 Basic molecular structure of rodic liquid crystals 6 1.3.2 Discotic liquid crystals 7 1.3.3 Amphiphilic liquid crystals 9 1.4 Polymorphism of Liquid Crystals 11 1.4.1 No translational order — Nematics 12 1.4.2 One-dimensional translational order — Smectic A and C phases 13 1.4.3 Two-dimensional translational order within layers with weak correlation along the third dimension — Hexatic phases 15 1.4.4 Three-dimensional translational order but correlation is weaker than that in crystals 17 1.4.5 Chiral liquid crystals 19 1.4.6 Cubic phases 21 1.4.7 Discotic liquid crystals 23 1.4.8 Lyotropic liquid crystals 25 1.4.9 Induced liquid crystals 26 v “fm” — 2004/2/9 — page vi — #2 vi Contents 1.5 Continuum Theory of Liquid Crystals 27 1.5.1 Order parameter 27 1.5.2 Distortions of liquid crystals 29 1.5.3 Frederiks transitions 31 1.5.4 The twisted – and supertwisted – nematic liquid crystals 34 1.6 Defects in Liquid Crystals 35 1.6.1 The Volterra process 36 1.6.2 Strength of disclination in nematics 38 1.6.3 Point disclinations 42 1.6.4 Defects in smectic A phase 44 1.6.5 Defects in the smectic C phase 47 1.6.6 Dispiration in the smectic C* phase 47 1.6.7 Defects in the cholesteric phase 47 1.6.8 Textures 49 1.6.9 Homotopy classification of defects in liquid crystals 50 2 Theories of Liquid Crystalline Polymers 53 2.1 Onsager Theory for Rigid – Rod Liquid Crystalline Polymers 54 2.1.1 The partition function 55 2.1.2 The excluded volume 61 2.1.3 The equilibrium of liquid crystals 62 2.2 Flory Theory for Rigid – Rod Liquid Crystalline Polymers 65 2.2.1 Partition function of a rigid rod solution 65 2.2.2 Formation of the liquid crystal phase 69 2.2.3 Two phase equilibrium 71 2.2.4 Effect of “soft” interaction between molecules 74 2.2.5 Semi-rigid chains 78 2.2.6 Discussion of the Flory theory 79 2.3 Comparison of the Onsager and Flory Theories 81 2.4 Maier-Saupe Mean Field Approach 86 2.4.1 Maier-Saupe mean field theory for small molecular mass liquid crystals 86 2.4.2 Freely-jointed-rod chains 88 2.4.3 Elastically-jointed-rod chains 90 2.4.4 Discrete and continuum chain models 95 “fm” — 2004/2/9 — page vii — #3 Contents vii 2.5 Worm Chain Model of Liquid Crystalline Polymers 96 2.5.1 Path integral description for polymers 96 2.5.2 Anisotropic conformation 99 2.5.3 Order parameter 101 2.5.4 Dependence of N–I transition on polymer chain length 101 2.5.5 Latent entropy at transition 102 2.6 Main Chain Liquid Crystalline Polymers with Spacers 103 2.6.1 Molecularly non-homogeneous liquid crystalline polymers 103 2.6.2 Pseudo-second-order-phase-transition temperature 108 2.6.3 Hinge effect 108 2.7 Side Chain Liquid Crystalline Polymers 110 2.7.1 Model 110 2.7.2 Phase classification of side chain nematic polymers 111 2.7.3 Order parameter and phase transitions 112 2.7.4 Conformations 115 2.8 Liquid Crystalline Networks 116 2.8.1 Conventional networks 117 2.8.2 Model of liquid crystal networks 119 2.8.3 Relation of stress and strain 121 2.9 Liquid Crystal Network Gels 124 2.9.1 Nematogetic network swollen by isotropic solvent 124 2.9.2 Nematogetic network swollen by nematic solvent 126 2.9.3 The shift of phase equilibria under the presence of force 131 3 Molecular Engineering of Liquid Crystalline Polymers 133 3.1 Introduction 133 3.2 Low Mass Liquid Crystalline Compounds and Mesogenic Units 138 3.2.1 Poly(1,4-phenylene)s 139 3.2.2 Incorporation of “side-steps” 139 “fm” — 2004/2/9 — page viii — #4 viii Contents 3.2.3 Incorporation of kinked elements 142 3.2.4 Incorporation of flexible spacers 143 3.2.5 Terminal or end-on substitution 143 3.2.6 Lateral or side-on substitution 145 3.3 Molecular Weight and Molecular Weight Distribution 147 3.4 Main Chain Liquid Crystalline Polymers 155 3.5 Liquid Crystalline Polymers of the Side-Group Type with End-on Attachment 166 3.5.1 Synthesis 166 3.5.2 Structure and properties 171 3.6 Liquid Crystalline Polymers of the Side-group Type with Side-on Attachment and “Mesogen-jacketed Liquid Crystal Polymers” 177 3.7 Liquid Crystalline Polymers without Mesogenic Units 188 4 Characterization of Liquid Crystalline Polymers 195 4.1 Polarizing Optical Microscopy (POM) 197 4.1.1 Optical basics for POM 198 4.1.2 Orthoscopic observation 201 4.1.3 Conoscopic observation 206 4.1.4 Textures of polymeric liquid crystals 209 4.2 Differential Thermal Analysis (DTA) and Differential Scanning Calorimetry (DSC) 221 4.3 X-Ray Diffraction 228 4.4 Other Methods 237 4.4.1 Miscibility testing 237 4.4.2 Infrared dichroism 238 4.4.3 NMR study 240 4.4.4 Small-angle neutron scattering 241 5 Liquid Crystalline Polymers as High Performance Fiber and Structural Materials 245 5.1 Introduction 245 5.2 Liquid Crystalline Aromatic Polyamides 246 5.3 Liquid Crystalline Aromatic Heterocyclic Polymers 254 5.4 Thermotropic Liquid Crystalline Polymers 259 5.4.1 Type-1 copolyesters 261 5.4.2 Type-2 copolyesters 264 5.4.3 Type-3 copolyesters 268 5.5 Composites Reinforced by Liquid Crystalline Polymers 271 “fm” — 2004/2/9 — page ix — #5 Contents ix 6 Physical Properties and Applications of Liquid Crystalline Polymers 285 6.1 Elastic Properties of Liquid Crystalline Polymers 285 6.2 Viscosity and Rheology of Liquid Crystalline Polymers 300 6.3 Cholesteric Liquid Crystalline Polymers 315 6.3.1 Optical properties of cholesteric liquid crystals 315 6.3.2 Lyotropic cholesteric liquid crystalline polymers 318 6.3.3 Thermotropic cholesteric liquid crystalline polymers 326 6.4 Non-Linear Optical Liquid Crystalline Polymers 329 6.5 Ferroelectric Liquid Crystalline Polymers 341 6.6 Applications of Liquid Crystalline Polymers in Information Storage 350 6.6.1 Nematic liquid crystalline polymers 350 6.6.2 Smectic liquid crystalline polymers 352 6.6.3 Cholesteric liquid crystalline polymers 353 6.6.4 Photo-isomeric change 354 References 355 Index 371

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