Helix compensation, chiral nematics

As witli tlie nematic phase, a chiral version of tlie smectic C phase has been observed and is denoted SniC. In tliis phase, tlie director rotates around tlie cone generated by tlie tilt angle [9,32]. This phase is helielectric, i.e. tlie spontaneous polarization induced by dipolar ordering (transverse to tlie molecular long axis) rotates around a helix. However, if tlie helix is unwound by external forces such as surface interactions, or electric fields or by compensating tlie pitch in a mixture, so tliat it becomes infinite, tlie phase becomes ferroelectric. This is tlie basis of ferroelectric liquid crystal displays (section C2.2.4.4). If tliere is an alternation in polarization direction between layers tlie phase can be ferrielectric or antiferroelectric. A smectic A phase foniied by chiral molecules is sometimes denoted SiiiA, altliough, due to the untilted symmetry of tlie phase, it is not itself chiral. This notation is strictly incorrect because tlie asterisk should be used to indicate the chirality of tlie phase and not tliat of tlie constituent molecules. 

A nonphotochromic chiral compound, chiral (Fig. 10.7), which was derived with (1 s, 2R, 5S)-( + )-menthol, was found to give a right-handed helix by addition in E44. Contrary to chiral, m-azo-8 gave a left-handed helical helix within E44. Therefore, when both chiral compounds are added in E44, the opposite helical senses of chiral and m-azo-8 each compensate the other s EITP, leading to a compensated nematic phase. 

Polymers, e.g., polypeptides, form chiral lyotropic liquid crystalline phases T. and E. Samulski calculated the mutual van der Waals-Lifshitz forces between rod-like particles with chiral polarizability in an isotropic dielectric medium and therewith explained the phase chirality of polypeptides in organic solvents like dioxane. Furthermore, they showed that the use of different solvents can cause different handedness of the helix for the same solutes and that suitable mixtures of such solvents can result in compensated (i.e., nematic) mixtures although the polypeptide is chiral [4]. Solvent-... 

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