Calamitic liquid crystals parameters

Although the / —> N transition is the most studied one in liquid crystals, there are still fascinating problems that are not completely resolved. Landau argued that for purely geometrical reasons the transition should be first order, but after a flurry of experimental measurements in the 1960s and 1970s, the challenge became to explain why it was observed to be so weakly first order in calamitic liquid crystals. A key parameter of the transition is the value of T( - i.e., the difference between the actual transition temper-... 

The average orientational direction of the molecules is denoted by the director, n,with the degree of orientational correlation evaluated by the order parameter, S, expressed as in Eq. (8), where 0 is the angle between a molecule and the director. It is the nematic phase of calamitic molecules that is used in liquid crystal displays. 

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]. 

Figure 7. Molecular order in calamitic side-group polymers (a) Spacer model, (b) 3D-MAS-NMR spectrum of of a polysiloxane liquid crystal polymer, (c) order parameters of different segments of the molecule. For details see [48].

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