Orientational Oscillations in Homeotropic Layers of Liquid Crystals Induced by Low Frequency Pressure Gradient in the Presence of Stabilizing and Destabilizing Electric Field

Abstract

The results of optical investigations of periodical orientational changes in homeotropic layers of nematic liquid crystals distorted by low frequency (< 1 Hz) pressure gradient are presented. The experiments were carried out using the liquid crystal cells with space inhomogeneities induced by electric field, or by the variation of the local thickness of the layer. The LC MBBA with a negative sign of a dielectric permittivity anisotropy (Δ˜) and two nematic mixtures with positive sign of Δ˜ were used to investigate the electric field influence on the mechanic-optical response. It is established, that maximal value δm of phase difference between an extraordinary ray and an ordinary one is proportional to the square of amplitude of a pressure gradient for all LCs both in the absence and in the presence of electric field. It is in accordance with linear theory predictions and can be used for an elaboration of high sensitivity liquid crystal sensors. In quasi-stationary limit when the director motion is in a phase with pressure gradient oscillations the universal functions describing the relative phase difference were obtained and compared with the experimental results.