A New Method for Inducing Homeotropic and Tilted Alignments of Nematic Liquid Crystals on Silica Surfaces
Homeotropic alignment of a nematic liquid crystal on a silica surface can be induced by means of a prior treatment of the surface with a long-chain aliphatic alcohol or a mixture of such an alcohol and an amine. The treatment is presumed to replace some or all of the hydroxy groups normally attached to silicon atoms at the surface with alkoxy groups derived from the alcohol, thereby reducing the critical surface tension of the surface. As the chain length of the alcohol is decreased, the director of the nematic tilts away from the perpendicular orientation. The direction of tilt can be controlled by shallow angle ion beam etching the silica surface prior to the alcohol treatment, in which case the nematic molecules are uniformly tilted toward the ion beam source. The tilt angle is a function of both the length of the alcohol chain and the composition of the liquid crystal. Tilted homeotropic alignment is essential for obtaining optimum performance of field effect devices that use nematics with a negative dielectric anisotropy.
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