Static Strain Waves in Cholesteric Liquid Crystals: Response to Megnetic and Electric Fields

Abstract

Static strain waves appear for cholesteric liquid crystals confined between parallel plates treated to give homeotropic boundary conditions whenever the plate spacing exceeds a critical thickness which depends upon applied magnetic or electric fields. The periodicity of the strain wave varies with plate spacing and field. In practice it is possible to employ time effects to force the periodicity away from equilibrium. On a computer the periodicity can be treated as an independent variable. A three-dimensional phase diagram with plate spacing, field and periodicity as axes is studied by computer solutions of the torque equations. The director fields are described in terms of a set of parameters which allow one to visualize the complex patterns they take and how these patterns vary throughout the region of the phase diagram for which the periodic solutions exist. The fields considered are restricted to those which either force the director field to lie along the perpendicular to the plate (positive anisotropy) or to avoid that direction (negative anisotropy). The conditions for producing what are essentially field stabilized Bloch walls are described.