Liquid crystals (LCs) are substances possessing one or more mesophases between their liquid and solid phase. The sequence of these mesophases represents a step by step ordering of the structure. The nematic (N) phase is characterized by an orientational order of the elongated molecules described by the director n, but the centers of mass of the molecules are arranged randomly. In the smectic (Sm) phases besides the orientational order the centers of mass of molecules form a layered structure. The smectic-A (SmA) phase has no positional order within the layers, while the smectic-B (SmB) phase is characterized by a long-range hexagonal order in each layer and by a weak correlation between the layers. The features of these and other LC phases are described in detail in the literature - see e.g. [1-3].
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