Study of Phase Separated Polymer Dispersed Liquid Crystal Composite Films - Malik, Praveen (My University, 2006)
The main objectives for carrying out the present researchwork were: to standardize polymer dispersed nematic and ferroelectric liquid crystal films, to study the droplet morphology of aligned and unaligned liquid crystal materials in polymer matrix, to study the influence of dichroic dyes on the structure-property relationship in materials and to study the electrical and electro-optic properties of PDLCs with and without dye aditices. Thesis has been divided into five chapters as summarized below: Chapter 1 reviews basic concepts of liquid crystal in general with an emphais on polymer-dispersed liquid crystal systems. The techniques adopted for serveral studies and the possible applications have been review and presented. Chapter 2 describes experimental method for meterials preparations and techniques for measurement of physical parameters like electro-optic, thermo-optic etc and selection of appropriate materials for polymer dispersed nematic liquid crystal (PDNLC), systems. To prepare these films a mematic (NLC), ferroelectric (FLC), anthraquinone dye and UV curable polymers namely (NOA-63, NOA65, NOA68, NOA-73) obtained from M/S Norland, USA were used. The optical textures were viewed under a polarizing microscope (OYLMPUS-MODEL BX-51P) interfaced with a hot stage (Linkam Model TP94 and THMS 600). In Chapter 3 we present experimental results on the dispersion of nematic liquid crystal in polymer matrix. The effect of temperature and applied voltage on LC droplet morphology and its transmission properties were studies. results have been interpreted on the basis of dielectric effects. The device showed an optical transmission of about 85% at a field strength of ~2V/um. We also prepared Guest-Host cells consisting of an anthraquinone dye dispersed first in liquid crystal adn then in the polymer. The influence of anthraquinone dichroic dye dispersed in PDNLC films on the droplet morphology, shape, orientation of NLC droplets has been given. Chapter4 we have made an attempt to study the influence of a novel room temperature FLC in the polymer matrix in aligned and unaligned configurations. The effect of plymer viscosity on liquid crystal droplet morphology, electro-optic properties adn optical properties in both systems (aligned and unaligned) has been described. Temperature dependence on switching responses, droplet morphologies have also been investigated and these results have been compared with ferroelectric liquid crystal mixture (without polymer dispersion). Chapter 5 summarizes the important features and results obtained from different phase separated composites systems as discussed in chapter 3-4. The future possiblities have been explored on the basis of above work for both and applied research point of view.
Keywords: Polymer; Liquid Crystal Composite Films