NONEQUILIBRIUM PHASE WINDING AND ITS BREAKDOWN AT A CHIRAL INTERFACE

We describe a nonequilibrium phase winding of the liquid-crystal direc tor at a flat cholesteric-isotropic interface. The physical origin of the driving force is a symmetry-allowed coupling between an equilibriu m helix structure and gradients in impurity concentration set up at an interface forced to move by displacing the sample in a temperature gr adient. We interpret these observations to evaluate the coupling const ant: \nu(c)\ = 3 x 10(-4) dyn/cm. A second transition is observed at h igher displacement speeds to an orientationally disordered state.