freely suspended liquid crystalline films

Contents
Foreword xi
Preface xiii
1Introduction1
1.1 Free-Standing Films—History 1
1.2 Liquid Crystalline State of Matter 3
1.2.1 General Notions 3
1.2.2 Thermotropic Mesophases and Their Symmetry 4
1.2.3 Lyotropic Mesophases and Their Symmetry 9
1.2.4 Defects in Mesophases 9
1.3 Theory of Elasticity of Liquid Crystals 12
1.3.1 Order Parameter 12
1.3.2 Free Energy 15
1.4 Electro- (Magneto-) Optical Effects in Liquid Crystals 17
1.4.1 The Fredericks Transition 17
1.4.2 Flexoelectric Effect 18
1.4.3 Electrohydrodynamic Instabilities 19
1.4.4 Linear Electrooptical Effect in Ferroelectric Smectics 23
References 23
2Free-Standing Films—Basic Physical Notions and Properties25
2.1 Surface and Bulk Areas of a Film and Corresponding Order
Parameters25
2.2 ‘Thick’ and ‘Thin’ Films 27
2.3 Some Principles for the Molecular Organisation of Free-Standing
Films28
2.4 Surface Tension 30
2.4.1 Surface Tension and Anchoring Energy of Thermotropic
Mesophases and Free-Standing Liquid Crystalline Films30
2.4.2 Surface Tension of Lyotropic Mesophases and Freely
Suspended Liquid Crystalline Films32
2.5 Surface Viscoelasticity of Surfactant Monolayers 33
2.6 Pressure Inside Liquid Films 36
2.6.1 Capillary Pressure 36
2.6.2 Disjoining Pressure 37
2.6.3 Disjoining Pressure in Liquid Crystalline Films 38
2.6.4 The Pressure Balance in a Free-Standing Film 42
References 42
3Experimental Techniques44
3.1 Film Preparation 44
3.2 Film Thickness Measurements 47
3.3 Optical Microscopy 49
3.4 Polarisation-Optical Method 50
3.5 Ellipsometry 52
3.6 Calorimetry 52
3.7 Surface Tension Measurements 53
3.8 Structural Studies of Free-Standing Liquid Crystalline Films 56
3.8.1 Light Scattering and Reflection 56
3.8.2 X-Ray Scattering and Reflection 59
3.8.3 Electron Diffraction 60
3.8.4 Critical Reflection of Neutrons 60
4Thinning, Stratification and Rupture63
4.1 Main Stages of the Thinning Process 63
4.2 Mysels Classification of Thinning Free-Standing Films 64
4.3 Gradual Thinning or ‘Drainage’ 65
4.3.1 Hydrodynamic Expressions in Lubrication Approximation 65
4.3.2 Reynolds Films 67
4.3.3 Simple Mobile Films 68
4.3.4 Simple Mobile Soap Films. Role of Surface Viscoelasticity 70
4.3.5 Influence of Gravity on Film Thinning 71
4.3.6 Role of Surface Dimples in Film Thinning 74
4.4 Stratification 75
4.4.1 Stratification and Liquid Crystalline Ordering 75
4.4.2 Stratification Domains and Their Dynamics 78
4.4.3 Analogy Between Stratification, Wetting and Dewetting Phenomena82
4.5 Rupture of Free-Standing Films 83
References 87
5Orientational and Phase Transitions89
5.1 Orientational Transitions in Nematic Films 89
5.1.1 Experimental Data 90
5.1.2 The Generalised Parsons Model 92
5.2 An Example of Orientational Transition in Smectic C∗Films 96
5.3 Phase Transitions 96
5.3.1 Theory: Three-Dimensional Films—Role of Interfaces 97
5.3.2 Theory: Two-Dimensional Films 101
5.3.3 Experimental Data 104
References 110
6The Field-Induced Effects113
6.1 The Fredericks Transition 113
6.2 Flexoelectric Effect 114
6.3 Electrohydrodynamic Instabilities 115
6.3.1 Nematic Films 115
6.3.2 Smectic A Films 129
6.3.3 Smectic C and C∗films 130
6.4 Linear Electro-Optical Effect in Smectic C∗Free-Standing Films 130
References 131
7Structure and Defects of Stable Thin Films132
7.1 Structure 132
7.1.1 Thermotropic Smectic Films 132
7.1.2 Black Soap Films 133
a Newton black films 134
b Common black films 135
c Transition between Newton and common black films 136
7.1.3 Biomembranes 136
7.2 Defects 138
7.2.1 Two-Dimensional Defects 139
7.2.2 Defects and Phase Transitions 146
References 148
8Different Applications of Free-Standing Liquid Crystalline Films
150
8.1 Technical Use of Foams 150
8.2 Applications of Foams and Soap Films in Crystallography and
Mathematics152
8.3 Lyotropic Free-Standing Films—Use in Biology and Medicine 154
8.3.1 Biological Applications 154
8.3.2 Medical Applications 158
References 162
Index 163