Orientational instability of the director in a nematic cell caused by electro-induced anchoring modification

Abstract

We theoretically investigate the threshold for the director reorientation from the homeotropic state to the hybrid homeotropic-planar state and vice versa in a cell filled with a flexoelectric nematic liquid crystal (NLC) subjected to an electric field. The liquid crystal is doped by a CTAB-like substance, a part of molecules of which dissociates into positive and negative ions. The anchoring on one of the cell surfaces is assumed to be strong and homeotropic, while the other surface can adsorb positive ions which play the role of an orienting surfactant for NLC molecules on this surface. At certain voltages, the orientational transitions in the bulk of the NLC are possible due to the changing conditions for the director on the adsorbing surface. We calculate respective threshold voltages as functions of anchoring parameters. The existence of the critical values of these parameters, beyond which the orientational transitions do not take place, is established.