TEMPERATURE-DEPENDENCE OF THE DYNAMICAL BEHAVIOR OF HOLOGRAPHIC GRATINGS FORMED IN POLYMER-DISPERSED LIQUID-CRYSTAL FILMS

Using films made of liquid crystal (LC), pre-polymer and photoinitiato r dye mixtures: we fabricated holographic gratings under various curin g temperatures. Mixtures having LC contents of 20 wt% and 40 wt% were prepared. Qualitative studies on phase separation using these mixtures were first conducted using a light scattering method. We then investi gated the dynamical behavior of the gratings at various ambient temper atures. The grating morphologies were finally investigated using scann ing electron microscopy (SEM). The results showed that no macroscopic phase separation was observed in the samples which have a LC content o f 20wt%. The thermal grating was found to dominate in the initial peri od during the formation of gratings on these films. Later, it was offs et by the photopolymerization effect which eventually dominated and de termined the characteristics of the final grating. For samples having a LC content of 40wt%, the thermal grating effect was negligible, due to the molecular diffusions in these samples. The diffraction efficien cies of the final gratings were analyzed, and were found to have a goo d correlation with their SEM images.