Discotic liquid crystals parameters

Benzene-hexa-n-hexanoate (n = 5 in Fig. 5.5) has no discotic liquid crystal phase, but three condis states (phases III, II, I) The thermodynamic transition parameters are listed in Table 5.5. According to Eq. (1), one expects for fusion of the rigid crystal (phase IV) besides the ASp and 24 conformational contributions... 

J.K. Vij, A. Kocot, T.S. Perova, Order parameter, alignment and anchoring transition in discotic liquid crystals. Mol. Cryst. liq. Cryst. 397, 231-244 (2003)... 

Thennotropic liquid crystal phases are fonned by rodlike or disclike molecules. However, in the following we consider orientational ordering of rodlike molecules for definiteness, although the same parameters can be used for discotics. In a liquid crystal phase, the anisotropic molecules tend to point along the same direction. This is known as the director, which is a unit vector denoted n. 

McMillan s model [71] for transitions to and from tlie SmA phase (section C2.2.3.2) has been extended to columnar liquid crystal phases fonned by discotic molecules [36, 103]. An order parameter tliat couples translational order to orientational order is again added into a modified Maier-Saupe tlieory, tliat provides tlie orientational order parameter. The coupling order parameter allows for tlie two-dimensional symmetry of tlie columnar phase. This tlieory is able to account for stable isotropic, discotic nematic and hexagonal columnar phases. 

This interaction term, which is proportional to the first pseudoscalar term in a multipole expansion of the intermolecular interaction energy, as obtained by Goossens [79], [77], [80], was sufficient to obtain a rich polymorphism of chiral liquid crystal phases given by cholesteric and several blue phases in dependence on temperature and the chirality parameter c measuring the strength of the energy of chiral interaction, both for calamitic and discotic chiral Gay-Beme molecules [77], [81]. 

Internal and overall motions that take place on a dynamic scale from 10 to 10 s can affect the line shape of NMR powder spectra. This is often the case for phenyl ring rotations or chain isomeriza-tions in polymeric liquid crystals and for rotational diffusion in discotic mesophases. Line shape analysis allows different types of motions to be discriminated and the relative kinetic parameters to be obtained. Moreover multidimensional exchange NMR can be applied to characterize molecular details of dynamical processes when the correlation times range between 10 and 10 s. 

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