Preparation and Characterization of Dichroic Polymer Dispersed Liquid Crystals

Abstract

this thesis contains five chapters. Chapter first reviews basic features and classification of liquid crystals (LCs) in general and research works already accomplished by various research groups in the area of polymer dispersed liquid crystal (PDLC) and dichroic polymer dispersed liquid crystal (DPDLC) in particular. The liquid crystalline phases, the order parameter, and the liquid crystal alignments are defined, followed by the concepts of theory and liquid crystal deformations. The preparation methods of polymer dispersed liquid crystal (PDLC) and dichroic polymer dispersed liquid crystal (DPDLC) systems are given in detail. The operation principle of these PDLC and DPDLC system, liquid crystal droplet configuration with and without applied field, is explained. chapter second presents the experimental techniques for preparation and characterization of study the various PDLC, DPDLC, DPDFLC samples and their physical parameters. The characteristics of the dyes and the liquid crystals that were used in the experiments, along with their molecular structures, selection of materials and description of instruments, are also provided. Optical textures studies have been performed with optical polarizing microscope under different condition of sample preparation and temperatures. chapter three presents experimental results on the dispersion of nematic liquid crystal in polymer matrix with and without dye concentration. The morphological and electrooptical responses of dichroic polymer-dispersed liquid crystal films (DPDLCs) doped with anthraquinone and azo dichroic dyes have been studied in detail. For the preparation of DPDLCs, the polymerization-induced phase separation is considered using UV radiation curing process. chapter four, we have made an effort to prepare PDFLC and some dichroic PDFLC (DPDFLC) films of these materials by polymerization induced phase separation technique using ferroelectric liquid crystal, UV curable polymer NOA 65 doped with anthraquinone blue dye. An effort also has gone in detail to investigate their FLC properties in UV curable adhesive with varying concentration of dye. The detailed investigation of droplet morphology, droplet orientation and optical responses such as transmission, spontaneous polarization, threshold voltage, contrast ratio, and response time as a function of applied voltage, temperature and dye concentration are given. These films show microseconds switching response and higher transmission at low dye concentration. where as chapter five contains the conclusions of the work which has been done in the thesis.