Photopolymerization and Electrooptic Properties of Polymer Network/Ferroelectric Liquid-Crystal Composites

Abstract

Polymer/liquid crystal (LC) composites have recently been the focus of considerable attention. One group of these composites, namely polymer stabilized ferroelectric liquid crystals (PSFLCs), show great potential for display technology due to the inherently fast switching speed of the liquid crystal and the mechanical strength imparted by the polymer. This study examines the effects of introducing polymer networks into a ferroelectric liquid crystal (FLC) and the polymerization behavior of cross-linking monomers in the ordered media of an FLC. Phase behavior changes significantly after addition of monomer, but upon polymerization the phase transitions return close those of the pure FLC. On the other hand, electro-optic properties of the system, such as the ferroelectric polarization, are changed significantly by introducing a polymer network. These changes are highly dependent on the monomer structure and the LC phase in which polymerization is initiated. The polymerization behavior is also highly dependent on the order of the media. As the order of the LC phase increases, the rate of polymerization increases significantly for both mesogenic and non-mesogenic monomers. This behavior occurs as the monomers segregate within the LC, increasing the local monomer concentration and thus the polymerization rate.