Optimization of performance of holographic gratings was investigated by changing the chemical structures of photopolymerizable monomers, the LC content, and recording beam intensity, which strongly related to the control of kinetics of polymerization and phase separation of LCs. High diffraction efficiency was obtained using 3-acryloxypropyltrimethoxysilane (APTMS) and 2-[(3,4-epoxycyclohexyl)ethyl]trimethoxysilane (ECTMS) as siloxane-containing reactive diluent by inducing a fast and good phase separation originated from the incompatible and flexible properties of siloxane chain even at a very low LC concentration (10~25wt%), in contrast to the case using diluent without siloxane component, like N-vinylpyrrolidinone. The phase-separated morphologies of gratings, such as spacing and surface topology, were observed by atomic force microscopy (AFM). Very regular and smooth morphologies were observed for the formed holographic gratings with APTMS and various amounts of LC.
Liquid crystalline compounds with a siloxane component in the tail were found to be effective in the formation of holographic gratings of polymer dispersed liquid crystal systems over a wide concentration range from 3wt% to 30wt%. The structure of the siloxane chain had a big effect on the performance of the gratings. Fine gratings with a diffractive efficiency of 40wt% could be formed with a liquid crystalline compound containing 3wt% disiloxane.