Characterization and polymerization behavior of polymer-stabilized ferroelectric liquid crystals

Recently, the development and application of polymer/liquid crystal (LC) composites have become an area of great interest in LC research. One class of these materials, namely polymer stabilized ferroelectric liquid crystals (PSFLCs), shows great promise in improving upon existing ferroelectric liquid crystal (FLC) technology. Introduction of a polymer into an FLC increases the inherent mechanical strength, but may also detrimentally affect the desirable electro-optic properties. This work focuses on understanding the process of PSFLC formation, and in so doing, builds a foundation to allow for performance optimization by selecting appropriate polymeric materials and polymerization conditions.;An integral part of this formation process lies in the polymerization itself. The effects of liquid crystalline order on the polymerization were investigated by monitoring the polymerization using differential scanning calorimetry. The reaction kinetics and mechanisms were examined for a variety of monomers polymerized at different temperatures corresponding to the various LC phases of the FLC. Interestingly, as the polymerization temperature decreased and the liquid crystalline order of the medium increased, a dramatic increase in polymerization rate was observed. This rate acceleration was seen in polymerizations of a number of monomers with different chemical structures and in a variety of different smectic LC materials. For some systems the rate increase was driven by a decrease in the termination rate, whereas in other polymerizations increases in both the apparent termination and propagation rates were observed. By using X-ray diffraction as well as polarized infra-red spectroscopy, the role of monomer segregation in the mechanisms driving these reaction behaviors was explored. These techniques demonstrated that some monomers segregated between the smectic layers, whereas others appeared to mimic the liquid crystals and segregate in the layers. Both types of segregation acted to reduce the reaction volume, thereby increasing the concentration of double bonds. Taking this segregation behavior into account, the polymerization behavior of certain monomer/FLC systems was also modeled.;Additionally, the electro-optic properties and optical characteristics were examined for PSFLCs formed with different polymers and under different polymerization conditions. Both ferroelectric polarization and optical response time depended heavily on the type of polymer as well as the temperature at which the monomer was polymerized. Although these properties exhibited by the PSFLC materials were typically much different than those of the neat FLC, by selecting appropriate monomer systems and polymerization conditions, the electro-optic characteristics were optimized and values very close to those exhibited in the FLC were achieved.