Bipolar Electrodiffusion model for Electroconvection in Nematics

The common description of the electrical behavior of a nematic liquid crystal as an anisotropic dielectric medium with (weak) ohmic conductivity is extended to an electrodiffusion model with two active ionic species. Under appropriate, but rather general conditions the additional effects can lead to a distinctive change of the threshold behavior of the electrohydrodynamic instability, namely to travelling patterns instead of static ones. This may explain the experimentally observed phenomena.