Conductivity Differences in the Cholesteric Textures

Abstract

Both the focal conic and Grandjean textures can be characterized by a conductivity tensor with uniaxial symmetry. We have observed that the diagonal element corresponding to the conductivity in the special direction is ≈ 20% larger in the focal conic case. The film studied was a mixture of 80% N-(p-methoxybenzyli-dene)-p-butylaniline and 20% cholesteryl oleyl carbonate. The transformation to the focal conic texture was produced by the application of a dc voltage and the reverse transformation was induced by an ac voltage. At sufficiently low current levels, current does not perturb structure (at least to the extent that the optical and electrical properties are not altered). At higher levels, the measuring stimulus converts the film to an intermediate state and both textures approach the same current level since they are converted from their original symmetries into the same state. The conductivity differences observed are consistent with conductivity ratio data for the nematic component and the molecular distributions in the two textures. The influence of resistivity and temperature on the focal conic/Grandjean conductivity ratio is shown.