The factors of liquid crystal photoalignment on polymer films: Photoorientation versus self-assembling

The liquid crystal (LC) photo-alignment on the azopolymer films is discussed. As aligning materials we used azopolymalonates and azopolymethacrylates differing by the end substitutes in the azochromophores. The photostimulated self-assembling of azochromophores in the top layer of the aligning film is revealed to be an important factor of LC alignment. It may substantially modify alignment direction and anchoring parameters caused by the photoorientatiion of azochromophores determined by the light geometry. Depending on the chemical composition of liquid crystal, the self-assembled layers may influence either homeotropic or planar LC alignment. In the latter case azimuthal anchoring is extremely weak so that effective LC gliding can be realized. For the azopolymer with a low self-assembling efficiency tilted LC alignment is realized with the pretilt angle controllable in a range of 0 degrees-90 degrees.