Interface dynamics in liquid crystals

Abstract. We have experimentally observed the pattern instabilities of an Ising wall formed in a nematic or cholesteric liquid crystal layer. We have deduced an envelope equation, relevant close to the Freeder-icksz transition, from which we derived an equation for the dynamics of the interface in the vicinity of its bifurcation. In the case of the zig-zag instability, this model is characterized by a conservative and variational order parameter whose gradient satises a Cahn-Hilliard equation. We have also investigated the influence of slightly broken symmetries on the dynamical behaviour of the system. The disappearance of the interface translational invariance or of the reflection symmetry along the wall axis may induce new interfacial patterns which have been both experimentally and theoretically pointed out. PACS. 47.20.Ma Interfacial instability { 47.20.Ky Nonlinearity (including bifurcation theory) { 61.30.Gd Orientational order of liquid crystals; electric and magnetic eld eects on order