Elastic properties of smectic liquid crystals

Smectic liquid crystals possess partial positional orders besides the orientational order exhibited in nematic and cholesteric liquid crystals. Here we only consider the simplest case smectic-A. The elastic energy of the deformation of the liquid crystal director in smectic-A is the same as in nematic. In addition, the dilatation (compression) of the smectic layer also costs energy, which is given by [23] 

Some chiral liquid crystals, as temperature is decreased, exhibit the mesophases isotropic cholesteric — smectic-A. Because of the propoly shown by Equation (1.70), there is no 

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