Azimuthal anchoring of liquid crystals at the surface of photo-induced anisotropic films

Many electrooptic applications of liquid crystals require a uniform orientation of the director at the glass substrate. A new method to obtain alignment layers for this purpose is the induction of anisotropic properties in suitable polymer films by exposure to linearly polarized UV radiation. We demonstrate that the anchoring strength at these films can be continuously varied by choosing the appropriate exposure time. In particular, well-defined weak anchoring can be produced. Values of the anchoring energy are given for a system that shows photo-induced reorientation of dye molecules resulting from cis-trans isomerisation and a system with polarization-sensitive photo-crosslinking.