ELECTRICALLY-INDUCED UNIFORM PLANAR ALIGNMENT OF S-C-ASTERISK LIQUID-CRYSTALS ON HOMEOTROPICALLY TREATED PLATES

Chevron textures of S-C films are usually obtained with the conventio nal procedure where a planar alignment coating (e.g., buffed polyimide ) is used. We describe a new technique which enables us to obtain unif orm bookshelf textures which show bistability and can be switched with low fields (similar to 1 V/mu m). This is achieved with a homeotropic surface coating. With a homeotropic coating the samples form a unifor m texture with horizontal layers on cooling. The homeotropic texture b ecomes unstable under sufficiently strong electric fields and transfor ms to a birefringent texture with smectic layers oriented vertically. Without an additional bias the texture has domains of different layer orientations. By simultaneous application of a vertical field and hori zontal shear stable uniform bookshelf textures can be obtained. Here w e show that it is possible to obtain uniform bookshelf alignment by th e simultaneous action of a horizontal field gradient and ac fields. Th e horizontal gradient leads to a more or less well-defined propagating front of the texture transformation. It results in a biased domain te xture with vertical layers. The effect of the strong ac field (similar to 100 Hz) is to smooth out the domain texture. (C) 1994 American Ins titute of Physics.