A liquid crystal (LC) at its boundary surface adopts a preferential alignment, which is referred to as anchoring. The direction of this alignment (i.e., anchoring direction) may be perpendicular, parallel or tilted with respect to the surface. Transitions from one anchoring condition to another may occur when the parameters (e.g., temperature) charactering the surface change, as referred to as anchoring transitions. In the LC-polymer composite systems under our study, the anchoring and temperature- driven anchoring transitions of nematic fluids is very sensitive to the structure of the side chain of poly (alkyl acrylate) matrixes that encapsulate the LC. We have shown that the anchoring transition temperature of these systems can be tuned far below the nematic-to-isotropic transition temperature, by varying either the length, branching structure of the side chains of homopolymers, or the composition of copolymer of two dissimilar monomers. Both sharp and broad anchoring transitions with respect to the temperature range over which a transition occurs were observed. It is postulated that microscopic interactions between the polymer side chains and LC molecules play an important role in determining the anchoring. In particular, the conformation of the polymer side chain is proposed to have important control over the anchoring. Anchoring strength and tilt angle as a function of temperature during the anchoring transitions were also experimentally investigated, which contribute to understanding of the microscopic mechanism for such transitions. Based on the LC-polymer composites with controlled anchoring, a LC display with reverse switching mode and a novel electrically switchable diffraction grating have been demonstrated. The advantages of these devices are ease of manufacturing, low operation voltage, and mechanical stability offered by polymer matrix. Moreover, a detailed study of the director configuration of wall defects found in these composite films was carried out using fluorescence confocal polarized microscopy.

Surface free energy of a polymer is of great importance in adhesive studies. Acid/base specific interactions play pertinent roles in adhesive bond performance and polymer-polymer miscibility. In this study, the correlation between the surface characteristics of two polymers and their adhesive bond behavior as well as the compatibility of their blend systems are investigated through both the surface characterizations and bulk examinations. Inverse Gas Chromatography (IGC) is employed to determine the surface free energies, the dispersive component and acid/base specific interactions, of polyethylene terephthalate (PET), cellulose acetate (CA) and their blend. Dynamic Contact Angle (DCA) measurements are performed to obtain the surface free energies of PET and CA so that they can be compared to that from IGC. Moreover, the DCA data are used to calculate their spreading coefficients and the adhesive bond behavior between PET and CA is predicted as well. The bulk examinations on specific interactions and the miscibility of the PET/CA , PBT/CA blends are completed through Fourior Transform Infrared-Diffuse Reflectance Spectroscopy (FTIR-DRIFT), Differential Scanning Calorimeter (DSC) and Dynamic Mechanical Analyzer (DMA). Scanning Electron Microscopy (SEM) micrographs of these blends are taken to examine their morphologies. From IGC, it is deterrnined that the surfaces of PET and CA are predominantly basic. The spreading coefficients calculated from DCA data indicate the poor adhesive bond between PET and CA. The bulk examinations reveal that both PET/CA and PBT/CA blends are immiscible systems. / Master of Science