SURFACE WALLS ON A BISTABLE ANCHORING OF NEMATIC LIQUID-CRYSTALS

We observe the defects separating nematic domains of two easy orientat ions, above a bistable orienting SiO evaporated glass plate. The defec ts are coreless walls. Their width depends on the bulk texture imposed by the nematic cell geometry. For thin enough samples, we have found situations where the wall thickness diverges, i.e., where the texture can force a surface orientation exactly along the surface barrier orie ntation. We model this new kind of surface transition. The barrier ene rgy of-the bistable anchoring is found small, with an extrapolation le ngth approximate to 1 mu m. We observe also hysteresis effects which c an be explained by a more or less permanent first molecular layer adso rbed on the surface. The corresponding non-elastic contribution to the anchoring is one order of magnitude larger than the elastic one.