Structure and properties of bubble domains in cholesteric nematic mixtures

Abstract

Textural laser diffraction and light-scattering studies on homeotropically aligned nematic material (MBBA) doped with cholesteryl nonanoate (CN) has been carried out with and without an applied ac (50 Hz) electric field. In the narrow range of the ratio of the pitch ρ to the thickness l of the cell, 1.2<p/I<2, one observes uniformly densely packed bubble domains which grow in size on application of an electric field. In the range p/I2, the bubble domains become visible only at certain applied electric fields which increase with a decrease in the CN concentration. These bubble domains constitute a cholesteric phase with the spiral axis perpendicular to the substrate in a matrix of homeotropically aligned nematic material. The increase in the bubble domain size on application of electric field constitutes a nematic → cholesteric transformation. Light scattering experiments indicate an optimum doping in relation to the threshold potential, contrast ratio, etc.