Electric field transport of biphilic ions and anchoring transitions in nematic liquid crystals

Abstract

Anchoring interaction of MBBA and MBBA + 5CB nematic layers with monomolecular films of CTAB on ITO glass supports is studied by videomicroscopy in the presence of an electric field. Planar-planar or homeotropichomeotropic electrode substrates are used to make the nematic cells. The substrate symmetry is broken by coating only one electrode with self-assembled CTAB film. In a DC electric field we observe some new effects; (i) polarity-dependent breaking of anchoring and switching to two oblique states in dielectrically stable planar cells; (ii) a polarity-dependent flow-induced metastable anchoring transition in homeotropic cells to a planar or tilted alignment after the field is switched off. These results are discussed in terms of a surface transition assisted by electric transport of biphilic CTAB ions and by a surface memorization of the flow-induced planar alignment.