Interface dynamics in liquid crystals

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 Freedericksz transition, from whi ch we derived an equation for the dynamics of the interface in the vicinity of itu bifurcation. In the case of the zig-zag instability, this model is characterized by a conservative and variational order parameter whose gradi ent satisfies a Cahn-Hilliard equation. We have also investigated the influ ence of slightly broken symmetries on the dynamical behaviour of the system . The disappearance of the interface translational invariance or of the ref lection symmetry along the wall axis may induce new interfacial patterns wh ich have been both experimentally and theoretically pointed out.