Mesogen

Abstract: A biaxial nematic phase had been predicted with ${D}_{2h}$ symmetry, wherein the mesogen's long and short transverse axes are simultaneously aligned along the two orthogonal, primary and secondary directors, $\mathbf{n}$ and $\mathbf{m}$, respectively. The unique low-angle x-ray diffraction patterns in the nematic phases exhibited by three rigid bent-core mesogens clearly reveal their biaxiality. The results of x-ray diffraction can be readily reproduced by ab initio calculations that explicitly include the bent-core shape in the form factor and assume short-range positional correlations.

Abstract: Synthesis, mesomorphism, orientation and photo-initiated chain crosslinking of the liquid-crystalline diacrylate 1,4-phenylene bis{4-[6-(acryloyloxy)hexyloxy]benzoate} (1) are studied. Monomer 1 exhibits a broad nematic phase between 108 and 155°C and a monotropic smectic phase below 88°C. The monomer is uniaxially oriented in its nematic phase at a substrate which has been coated with polyimide and unidirectionally rubbed with tissue. At the transition temperature to the smectic phase the order parameter is measured to be 0,7. During polymerization, the ordering of the mesogens is frozen-in, yielding a uniaxially crosslinked network. The clear films of oriented poly(1) exhibit a birefringence Δn between 0,12 and 0,15, depending on the polymerization temperature. In the highest oriented state of 1 a small reduction of the degree of order is observed during the crosslinking reaction, whereas at higher temperatures and lower ordering of 1, the uniaxially orientation increases upon reaction. A special feature of the oriented networks is that the ordering is maintained while heating at high temperatures. The polymerization of the acrylate groups in the mesomorphic phases proceeds fast and to high conversion. Below 90°C the polymerization behaviour is similar to that of conventional isotropic diacrylates. Above 90°C the polymerization reaction of the liquid-crystalline diacrylate proceeds faster than that of an isotropic diacrylate.

Abstract: Foreword - Introduction - Literature Part I STRUCTURE OF LIQUID CRYSTALS Chapter 1 Symmetry11 Point group symmetry12 Translational symmetry Chapter 2 Mesogenic Molecules and Orientational Order21 Molecular shape and properties22 Intermolecular interactions 23 Orientational distribution functions for molecules24 Principal orientational order parameter (microscopic approach)25 Macroscopic definition of the orientational order parameter25 Apparent order parameters for flexible chains Chapter 3 Liquid Crystal Phases31 Polymorphism studies32 Main calamitic phases33 Discotic and bowl-type phases34 Role of polymerization35 Lyotropic phases36 General remarks on the role of chirality 37 Cholesterics38 Blue phases39 Chiral smectic C* phase310 Chiral smectic A*311 Spontaneous break of mirror symmetry Chapter 4 Principles of Structure Analysis and X-ray Diffraction 41 Diffraction studies and X-ray experiment41 X-ray scattering43 Diffraction on a periodic structure44 Fourier transforms and diffraction45 X-ray Diffraction by Crystals46 Diffraction by the isotropic and nematic phase47 Diffraction by smectic phases Chapter 5 Phase Transitions51 Landau approach52 Isotropic liquid -- nematic transition53 Nematic-Smectic A transition54 Smectic A -- Smectic C transition55 Dynamics of order parameter56 Molecular Statistic Approach to Phase Transitions57 Nematic-isotropic transition (molecular approach)58 Phase transitions in magn & el fields Part II PHYSICAL PROPERTIES Chapter 6 Magnetic, Electric and Transport Properties61 Magnetic phenomena62 Dielectric properties63 Transport propertiesChapter 7 Elasticity and Defects71 Tensor of elasticity72 Elasticity of nematics and cholesterics73 Variational problem and elastic torque74 Defects in nematics and cholesterics75 Smectic phases Chapter 8 Elements of Hydrodynamics81 Hydrodynamic variables82 Hydrodynamics of isotropic liquids83 Viscosity of nematics 83 Flow in cholesterics and smecticsChapter 9 Liquid Crystal -- Solid Interface 91 General properties of interfaces92 Surface energy and anchoring of nematics93 Liquid crystal alignment Part III ELECTRO-OPTICS Chapter 10 Optics and Field Effects in Nematic and Smectic A Liquid Crystals101 Optical properties of uniaxial phases102 Fredericks transition103 Flexoelectricity104 Electrohydrodynamic instability Chapter 11 Electro-Optical Effects in Cholesteric Phase111 Cholesteric as one-dimensional photonic crystal112 Field instabilities of cholesterics113 Bistability and memory114 Flexoelectricity in cholestericsChapter 12 Ferroelectricity and anti-ferroelectricity121 Crystalline ferroelectrics122 Ferroelectric cells with a non-ferroelectric liquid crystal?123 Phase transition SmA*-SmC* 124 Electro-optical effects in ferroelectric cells125 Anti-ferroelectrics Subject index

Abstract: I: Synthesis, Structure, Properties Relationships.- 1. Synthetic Routes to Liquid Crystalline Polymers.- 2. Chiral Thermotropic Liquid Crystal Polymers.- 3. Solid State Physics of Thermotropic Polyesters: Internal Friction of Mesomorphic Structures.- 4. Thermotropic Liquid Crystal Aromatic Copolyesters Containing Cycloaliphatic Units.- 5. Polymerization of Allyldimethyldodecylammonium Bromide Liquid Crystalline Monomer to Its Liquid Crystalline Polymer.- II: Theory.- 6. Theoretical Basis for Liquid Crystallinity in Polymers.- 7. Nematic Liquid Crystals Formed from Flexible Molecules: a Molecular Field Theory.- 8. Order and Odd-Even Effects in Thermotropic Nematic Polyesters.- III: Characterization.- 9. Structure and Characterization of Thermotropic Liquid Crystalline Polymers.- 10. Observations on the Rheology of Thermotropic Polymer Liquid Crystals.- 11. Rheo-Optical Studies of the Thermotropic Aromatic Copolyesters of Poly(Ethylene Terephthalate) and p-Acetoxybenzoic Acid.- 12. Electron Microscopy of Thermotropic Copolyesters.- 13. Nuclear Spin-Label Studies of Liquid Crystal Polymers.- 14. Viscosity and the Thermodynamic Properties of Liquid Crystalline Polymers with Mesogenic Side Groups.- 15. Measurement of Orientational Order in Liquid Crystalline Samples by NMR Spectroscopy.- 16. Phase Behaviour of Dye-Containing Liquid Crystalline Copolymers and Their Mixtures with Low Molecular Weight Liquid Crystals.- 17. Dielectric Relaxation Measurements and X-ray Investigations of Liquid Crystalline Side-Chain Polymers.- 18. Structural Investigations on Liquid Crystalline Side-Chain Polymers.- 19. Macromolecular Order and Conformation in the Solid and Nematic Phases of Semi-Rigid Polymers and Polymer-Monomer Mixtures-NMR Study.- IV: Applications.- 20. Aramids-Bridging the Gap between Ductile and Brittle Reinforcing Fibres.- 21. Towards a Photoconductive Liquid Crystal: Carbazole-Containing Systems.- 22. Electro-Optic Effects in a Smectogenic Polysiloxane Side-Chain Liquid Crystal Polymer.