On Molecular Structure and Physical Properties of Thermotropic Liquid Crystals

Some models for the molecular structures of liquid crystals including a ferroelectric liquid are discussed. It is shown that a smectic liquid with a layered structure, in which the preferred orientation of the molecular axis is inclined against the layers, has some similarities with a nematic liquid. Such a tilted smectic liquid may also have a twisted modification corresponding to a twisted nematic or cholesteric liquid crystal. Attention is drawn to an optically isotropic texture of a cholesteric liquid. A proposal is made for its molecular structure in which a fairly regular, lattice-like arrangement of alignment singularities is assumed. Twist waves in nematic liquids are regarded and numerical estimations are made for their wave velocity and damping in p-azoxyanisole. It is concluded that the damping is too strong for an observation of such waves.