Polymerization Conditions and Electrooptic Properties of Polymer-Stabilized Ferroelectric Liquid Crystals

Abstract

Electrooptic and optical characteristics of polymer-stabilized ferroelectric liquid crystal (PSFLC) materials prepared under different conditions were characterized. Polymerization behavior and segregation properties were also investigated. The rate of polymerization during formation of PSFLCs increases significantly as the order of the LC phase increases and the temperature decreases for the monomers employed. Although the polymerization behavior is similar for these different monomers, trends in electrooptic behavior are considerably different. For C6M and p-phenylene diacrylate PSFLCs polymerized in ordered liquid crystalline phases, the temperature of polymerization and the corresponding liquid crystalline phase in which the polymerization occurs have little impact on the ultimate electrooptic and optical properties. The electrooptic properties of 1,6-hexanediol diacrylate (HDDA) PSFLC systems, on the other hand, show a large dependence on the polymerization temperature. Both the ferroelectric polarization and the optical response time increase with polymerization temperature in the ordered phases. Additionally, the optical characteristics of HDDA PSFLCs observed in the smectic C* phase change considerably, as the polymerization temperature is varied within the ordered LC phases. For all of the materials studied, if the polymerization is carried out in the isotropic phase, the polymer has no imparted order and prevents any bulk alignment, thereby detrimentally affecting the electrooptic characteristics. Using these results, the electrooptic and optical properties can be optimized by using appropriate monomer/FLC mixtures and polymerization temperatures.