Electrodynamics of Liquid Crystals

Abstract

It is well known that in crystals the centres of gravity of the atoms or molecules are located on a three-dimensional periodic lattice. In the liquid, the centres of gravity are not ordered in this sense. As a result, the states of matter differ by their mechanical properties; for example, a liquid flows easily. Certain organic materials do not show a single transition from solid to liquid, but rather a cascade of transitions involving new phases. The mechanical properties and the symmetry properties of these new phases are intermediate between those of a liquid and those of a crystal. They have been called liquid crystals, or mesomorphic phases. From the point of view of electrodynamics, liquid crystals are strongly anisotropic, dispersive and, in general case, inhornogeneous media. Therefore, the study of liquid crystals behavior in external magnetic and electric fields and of electromagnetic wave propagation in liquid crystals is very instructive and presents some interesting illustrations for the formalism developed in previous chapters. We consider first very briefly some essential features of liquid crystals which are necessary for the further analysis.