Director tilting of liquid crystals on photoisomerizable polyimide alignment layers doped with homeotropic surfactant

Director tilting of liquid crystal (LC) molecules on photosensitive alignme nt layers has been investigated. The layers, polyimides with photoisomeriza ble groups in their main chains, were irradiated with unpolarized near-UV ( UPUV) light at oblique incidence. The irradiated film was found to align LC molecules homogeneously with a negligible pretilt angle. It was found that the pretilt angle can be generated successfully by introducing surfactant lecithin and decreasing the incidence angle of the UPUV light. The LC align ment and electro-optical properties of the LC cells with the photoalignment layers were demonstrated to be suitable for twisted nematic LC, vertical a lignment LC, and surface-stabilized ferroelectric LC devices. (C) 1999 Amer ican Institute of Physics. [S0021-8979(99)04216-4].