Liquid crystal theory

A. Jakli, J. Harden and N. Eber, Chapter 3. Flexoelectricity of bent-core molecules. In eds. A. Buka and N. Eber, Flexoelectricity in Liquid Crystals. Theory, Experiments and Applications, Imperial College Press, London, 2012. pp. 61-99. 

FLEXOELECTRICITY IN LIQUID CRYSTALS Theory, Experiments and Applications... 

J.L. Ericksen, "Singular Solutions in Liquid Crystal Theory", in "Liquid Crystals and Ordered Fluids", J.F. Johnson and R.S. Porter, Eds., Plenum, Hew York 1970. 

Liquid crystal theory involves explicit consideration of molecular alignment, and how this is affects or is affected by changes in temperature, flow conditions, concentration of solvents, etc. It seems clear that modifications in continum theory are needed to cope with complications encountered in liquid crystal polymers. As I see it, some of the fault is associated with simplistic assumptions about directional ordering employed in theories of nematics, so It seems worthwhile to review some of the thinking about such matters. 

Nonlocal radial dependence of laser-induced molecular reorientation in a nematic liquid crystal theory and experiment... 

J. C. Khoo, T. H. Liu et al., Nonlocal Radial Dependence of Laser Induced Molecular Reorientation in a Nematic Liquid Crystal Theory and Experiment, J. Opt. Soc. Am. B (1987) 136... 

Figure 2.33. Photograph of Geoffrey H. Taylor, who advanced the liquid crystal theory for structure formation in anisotropic carbons.

An interesting area, which involves chiral liquid crystal properties, is that of temperature sensors, used, for example, in the diagnosis of skin cancer, as well as in peripheral blood circulation problems. Another application in the medical field is represented by nematic elastomer films or fibers of liquid crystalline polymers with mesogene in the side chain, that can be used in the manufacture of muscle prosthesis [28]. To optimize their performance for different applications, the current knowledge on the relationship between the structure and properties of liquid crystals should be extended. In addition to further development of liquid crystals and their applications, the liquid crystal theories represent a sound basis for other areas of interest. For example, liquid crystals can be used as model compounds for the study of molecular interactions and of their effects on self-organization in supramolecular chemistry. 

R. Blinc, Models for Phase transitions in ferroelectric liquid crystals Theory and experimental results, NATO ASI Ser., Ser. B, 290 [Phase Transitions Liq. Cryst.), 343 (1992) ... 

Buka A, Eber N (2013) Flexoelectricity in liquid crystals — theory, experiments and phcations. Imperial College Press, London... 

Finally, a few words about other liquid-crystal theories the mean-field theory of Maier and Saupe (1959, 1960) has been very successful in describing the behaviour of small-molecule liquid crystals, but it has been much less used for polymeric liquid crystals. Other important theories primarily applied to small-molecule liquid crystals are the Landau theory and its extension, the Landau--de Gennes theory. A detailed presentation of these theories, also including the Maier and Saupe theory, is found in Vertogen and de Jeu (1988). 

The contribution of 77,2 exhibits its maximum at 0=45 ° and is usually small because of the small coefficient. As this coefficient can only be determined fi-om the angular dependence of the viscosity, its determination is difficult. In the first investigation by Gahwiller [5], even the sign obtained for 7712 was incorrect. Therefore, and because of the minor interest this coefficient has been investigated only for a few liquid crystals. Theory and later determinations [5,8, 44-46] show that this coefficient is negative for usual liquid crystals. 

In some nematic liquid crystals (e.g., MBBA or azoberrzene liquid crystals), theories and experiments have shown that, when photoexcited, the molecules will undergo some stmctural or conformational changes (from trans state to cis state) and will exhibit unusually large orientational optical nonlinearities. Such electronic-oiientational nonlinearities are discussed earlier in Chapter 8. 

It is common in liquid crystal theory to use a representation for the director that automatically ensures n is a unit vector, for example,... 

J.L. Ericksen, Inequalities in Liquid Crystal Theory, The Physics of Fluids 9, 1205-1207 (1966). 

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