Nonrubbing Techniques for Alignment of Nematic Liquid Crystals: Fundamentals and Applications

Controlled liquid crystal alignment layers are a prerequisite for both a vast number of basic studies of material properties of liquid crystals (LCs) and their electrooptical applications. Almost all commercial LC displays utilize a rubbed polyimide (PI) film to control LC alignment. Although this technique has its own advantages, it also introduces manufacturing problems, for example, static charge buildup, dust particle accumulation and mechanical damage on drive elements. These drawbacks can be avoided with the use of rub free alignment techniques. There are two parts in this dissertation: Fundamentals and applications. In the fundamental part, three major techniques to align LCs without rubbing were investigated, which are SiO_{rm x} oblique evaporation, PI Langmuir-Blodgett (PI-LB) films and surface alignment induced by linearly polarized UV exposure of polymer films. In the application part, several novel LC devices are explored using these alignment techniques. For obliquely SiO_{rm x} evaporated surfaces, the LC alignment mechanism is well known. We reviewed its main properties in order to compare the LC alignment behavior on PI-LB films and films exposed by linearly polarized UV. A quantitative microscopic model is developed to elucidate the mechanism of LC alignment by linearly polarized (LP) UV exposure. This model successfully explains the origin of the optical retardation anisotropy and LC easy axis induced on these LP UV exposed films, which depend in the model on the angular distribution of photo-reaction products which in turn, follow an angular dependent first order rate law. Unambiguous evidence supporting our model is also presented. For the PI-LB film, the effect of dipping speed on PI-LB film order, pretilt angle generation, anchoring strength and pretransitional birefringence are studied. Evidence shows that an epitaxial growth mechanism is favored to describe the LC alignment behavior on PI-LB films. In chapter 7, a new configuration of a 4-domain TN display which dramatically simplifies 4-domain TN display fabrication is explored. Our 4-domain TN cell has D _2 symmetry and is composed of two left handed and two right handed TN subpixels. For the first time, we provide complete viewing angle data of 4-domain TN display. In chapter 8, two new configurations of high efficiency diffraction light valves are proposed; namely a modified two-domain tunable birefringence diffraction device(MTD-TBD) and an optically active diffraction(OAD) device. These two diffraction grating structures in principle give us 100% diffraction efficiency and polarization independence. Their electrooptical performances are tested.