Author: Sang Hwa Kim

Publisher:

Published: 2004

Total Pages: 141

ISBN-13:

The main objective of the dissertation is to develop polymer stabilized liquid crystals applications with the aim of fast switching liquid crystal devices. We have scrutinized the design of the experimental setup and the optimization of the polymerization condition. We evaluate and discuss various PSLC systems, including the study of morphology of polymer networks and the electro-optical characteristics. Optically compensated bend (OCB) nematic or pi-cell is known to exhibit a fast response time and wide viewing angle with compensated films. But this bend mode has a splay-bend transition problem. These splay and bend states are topologically distinct and for real display modes it should be operated with bend mode without splay state. We introduced a polymer stabilization of the bend nematic mode in which we used polymer network acts as the volume surfaces to stabilize the bend state of the nematic liquid crystal. The switching time of a polymer-stabilized bend nematic display shows a fast rise time of 1.2ms and a 8.8ms decay time, which is sufficiently fast for video display applications. A liquid crystal blazed grating having a prismatic polymer microstructure has been developed using polymer-stabilized optical pattern forming state of a cholesteric liquid crystal. The prismatic polymer structure is formed by photo-induced localization and polymerization of a small concentration of monomer onto one substrate nearest to the UV The light incident at different angles from the normal. Using these method periodical one-dimensional patterns with a prismatic shape of polymer can be structured at the surface. The optical diffraction properties of the gratings were evaluated by the application of electric field and light incident angles, corroborate the blazed grating of asymmetric reflective index modulation. The dissertation continues on the exploration of an application of the short pitch cholesteric liquid crystals. Uniformly lying helix (ULH) of a cholesteric liquid crystal is formed with an applied electric field and temperature to exhibit the flexoelectric effect. For flexoelectro optic device applications, a problem arises in that the unwinding of the cholesteric helix is generally not completely reversible, and can produce degradation of alignment. As a result, the electro optic device does not fully return to the ULH texture after the applied electric field is removed. To address such a problem, we employ the polymer stabilization technique to stabilize the uniform lying helix texture. By using a small concentration of polymer we are able to stabilize ULH texture without the application of an electric field and lead to a device with two switching modes, amplitude (flexoelectric, at low field) and phase (dielectric, at high field) modulation, exhibiting a sub-millisecond response time.