Propagative patterns in the convection of a nematic liquid crystal

Abstract

We show here that the convective instability of a nematic liquid crystal subjected to an A.C. electric field (the conduction regime), is never stationary, contrary to the widely accepted picture. Indeed, we have found that the roll structure translates uniformly along the wavevector direction. In the low frequency part of the conduction regime, the structure is rather homogeneous in space and travels at a very low velocity, while inside the high frequency part, the rolls are localized inside stable domains and the propagation velocity is higher by three orders of magnitude. Closer to the cut-off frequency, we have also found a novel time dependent state, where the amplitude of the rolls oscillates periodically in time.