Electric field induced deformations of twisted flexoelectric nematic layers

Electric field induced deformations of twisted nematic cell containing liquid crystalline material characterised by flexoelectric properties and positive dielectric anisotropy were studied numerically. Anisotropic boundary anchoring was taken into account by use of a model formula proposed for this purpose. It was found that the surface torques of flexoelectric nature lead to homeotropic director orientation on one of the boundary plates. In consequence, the untwisted state arises in which the director is aligned in one plane due to the orienting effect exerted by the other plate. The transition between the twisted and untwisted structures occurs continuously or discontinuously depending on the anisotropy of the surface anchoring strength. In the latter case, hysteresis was observed when the voltage applied to the layer was varied. The possibility of switching between bright and dark states in the transmissive cell with two polarisers and in the reflective cell with one polariser and mirror was shown.