Influence of flexoelectricity on electrohydrodynamic instabilities in nematics under AC fields

Abstract

We develop a one-dimensional theory of electrohydrodynamic instabilities in nematics under AC excitation by incorporating the flexoelectric terms. The results account for the following observations which were not adequately explained earlier: (1) the occurrence of oblique rolls (OR) at a thre- shold voltage Vth (v) up to a certain well defined frequency v which depends on the conductivity of the sample, (2) the occurrence of OR at voltages > Vth at which normal rolls are seen for some frequency range vc > v > vo, (3) the observation of 'chevronsf in the dielectric regime and (4) the occurrence of 'longitudi- nal' rolls with a field threshold for materials with a negative dielectric anisotropy close to the nematic - smectic transition point.