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.