Electro-optical effects in hybrid aligned flexoelectric nematic layers

Abstract

Liquid crystal cells with hybrid boundary anchoring, filled with nematic possessing flexoelectric properties, and subjected to external electric field, were studied numerically in order to find the influence of flexoelectricity on their behavior. Such layers may adopt three kinds of director structures: uniform planar, uniform homeotropic, and non-uniform which is intermediate between the former two. Stability of these structures depends on flexoelectric coefficients, anchoring strengths, thickness of the layer, dielectric anisotropy, and elastic constants. Changes of bias voltage cause transitions between them, which lead to electro-optical effects if the layers are placed between crossed polarizers. Three cases of transitions were considered: (i) transition between bright planar and dark non-uniform states, (ii) between dark planar and bright non-uniform states, and (iii) between dark homeotropic and bright non-uniform states. The director distributions in various states corresponding to various grey levels were calculated, and the electro-optic characteristics were obtained. The dynamics of the transitions between dark, bright, and intermediate states was determined taking into account the backflow effect. It was found that the transitions are faster when the nematic is devoid of flexoelectric properties.