PRETILT ANGLE GENERATION ON PHOTOREACTIVE POLYMER-FILMS

The mechanism of liquid crystal pretilt angle generation on photoreact ive polymer films doubly exposed to linearly polarized ultraviolet (uv ) light has been investigated. The first exposure for time; tau(1) is normal to the surface, and the film is subsequently irradiated for tim e tau(2) With obliquely incident uv light with a plane of polarization rotated by 90 degrees with respect to that of the first uv light. The state of the polymer film after two exposures was characterized with a tensor order parameter, which then served as a boundary condition fo r the surface state of the nematic liquid crystal. The bulk liquid cry stal behavior was investigated using Landau-de Gennes theory extended to include the possibility for weak surface interactions linear in the tensor order parameter. The pretilt angle was calculated as a functio n of both tau(1) and tau(2), and as a function of the second uv light angle of incidence. The calculated behavior of the pretilt angle was f ound to be in qualitative agreement with experimental observations. Co nclusions about the strength of the anchoring have also been made.