Surface controlled nematic bistability

Abstract

One discusses phenomenologically the statics and dynamics of surface anchoring of nematic liquid crystals. In statics, for symmetrical situations, one can induce, under the action of an external field, a surface breaking with a bifurcation between two opposite orientations of the director. In dynamics, one shows that the surface director relaxation is intrinsically fast, and accompanied by a transient surface shear flow. In thin cells with planar anchorings, filled by cyanobiphenyl materials which orient normal to the plates under a strong electric field, there are now two effects which couple the relaxation of the surface director: a static one, which favors parallel orientation and a uniform cell texture, and a transient dynamical coupling from the surface flow, which forces π-twisted texture. With suitable electric signals, one can control the surface bifurcations to give at will one of these two bistable textures. Results are presented which show that these mechanisms could lead to a new class of surface controlled, fast nematic bistable displays.