| This thesis is focused on the alignment properties of liquid crystals controlled by the surface.; A new alignment technology utilizing Atomic Force Microscope (AFM) rubbing is used to control liquid crystal alignment down to nanometer length scales. This technology allows us to make pixelized patterns on polyimide surface, with a different easy axis in each pixel. The anchoring properties due to AFM rubbing were quantitatively studied. The effective polar and azimuthal anchoring strength coefficients for planar anchoring were determined as a function of the spatial separation L of rub lines. Based upon these results, several electrooptical devices were designed and tested, including an ultra-high resolution liquid crystal display architecture and optical gratings.; AFM rubbing technology was also used to investigate the nematic-isotropic (NI) phase transition. Spatially varying herringbone patterns with an easy axis alternating in angle ψ, for 0 < ψ < π, were created on a polyimide-coated surface. Compared to the uniformly rubbed surface, this patterned surface depresses the NI transition temperature. The relationship between the depression of the phase transition temperature and the angle ψ is measured and compared with a theoretical model.; The general property of the homeotropic alignment polyimide SE1211 was also studied. Under proper baking and rubbing condition, the pretilt angle could be continuously controlled from 0° to 40°. Also, because the coefficient of the quartic term of the anchoring strength of this polyimide is negative, we successfully observed a first order Fréedericksz transition under a single external field just above the nematic-smectic phase transition.; Although not related to surface behavior, this thesis also includes an experimental observation of the Fréedericksz transition of an antiferoelectric liquid crystal (AFLC). This experiment supports the two-layer two-step switching process from anticlinic to synclinic phase. |
