Liquid crystal phase applications

We are all familiar with tire tliree states of matter gases, liquids and solids. In tire 19tli century the liquid crystal state was discovered [1 and 2] tliis can be considered as tire fourtli state of matter [3].The essential features and properties of liquid crystal phases and tlieir relation to molecular stmcture are discussed here. Liquid crystals are encountered in liquid crystal displays (LCDs) in digital watches and otlier electronic equipment. Such applications are also considered later in tliis section. Surfactants and lipids fonn various types of liquid crystal phase but this is discussed in section C2.3. This section focuses on low-molecular-weight liquid crystals, polymer liquid crystals being discussed in tire previous section. 

Molecular mechanics force fields have largely been parameterised using the best available data from the gas phase and (in some cases) from liquid phase or solution data. The question therefore arises as to how applicable molecular mechanics force fields are to predicting structures of molecules in the liquid crystal phase. There is now good evidence from NMR measurements that the structure of liquid crystal molecules change depending on the nature of their... 

Table 5.1 Interaction of light with liquid crystal phases and their applications...

The first application described was as temperature sensors by using a chiral nematic liquid crystal, which displays different colors at different temperatures. It is also worth noting that many common fluids are in fact liquid crystals. Soap, for instance, is a liquid crystal, and forms a variety of liquid crystal phases depending on its concentration in water. 

In an interesting application, the long-chain substituted 4- -hexoxybenzylidene-4 -iodoaniline (HBIA), 5 has been incorporated in the liquid-crystal phase of 4- -hexoxy-benzylidene-4 -propylaniline (HBPA, 6)13. The intensity pattern of the Mossbauer spectrum allowed the orientation of the molecule to be estimated, showing that the smectic tilt angle was 50°. 

Another saturated tetrahydrofuryl core has found application as a component of liquid crystals. Cholesteric liquid crystal polymers are useful as photostable UV filters in cosmetic and pharmaceutical preparations for the protection of human epidermis and hair against UV radiation, especially in the range 280-450nm <2000DEP19848130>. Fused bifuran 81 is a suitable monomer for the preparation of these desired polymers as it contains the requisite characteristics of having more than one chiral, bifunctional subunit type which is capable of forming a cholesteric liquid crystal phase with a pitch of <450 nm. It also contains an achiral aromatic or cycloaliphatic hydroxyl or amino carboxylic acid subunit, achiral aromatic or cycloaliphatic dicarboxylic acids, and/or achiral aromatic or cycloaliphatic diols or diamines. Polymers prepared from suitable monomers, such as diol 81, can also be used as UV reflectors, UV stabilizers, and multilayer pigments. 

It is considered that liquid crystals that are soft and have long-distance order may form certain complex hierarchical structures other than blue phases. In fact, recent discoveries of new liquid crystal phases have arisen one after another. While many think of liquid crystals as display materials with the range of applications seemingly exhausted, it is more likely that applications other than displays are only beginning to appear. 

The local symmetry group of the Sc phase is a C2 group and thus the Sc phase has helical electricity. The spontaneous polarization, Ps, is perpendicular to the layer normal and molecular axis. Due to its helical structure Ps changes its direction uniformly, evolving along the helical axis so that the Sc phase does not show a measurable ferroelectricity except in the unwinding of its helical structure. The Sc phase is one of the very important liquid crystal phases that has a prospective application in fast response display. The detailed structure of the Sc phase will be shown in Chapter 6. 

Probably, the single most important characteristic of liquid-crystal phases is that as fluids they are anisotropic " this means that their physical properties are likewise anisotropic, and it is this feature which is the basis for the widespread application of the materials and also, in many cases, of their characterization. 

The applicability of homotopic theory becomes much less obvious for liquid crystal phases with more complicated order parameters such as biaxial nematics and cholesterics, which are both locally defined by three directors forming a tripod. This gives rise to a description of the line singularities in terms of the quaternion group, Q. This is particularly interesting because the quaternion group Q is non-Abelian, a property that... 

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