Control of morphology and diffraction efficiency of holographic gratings using siloxane-containing reactive diluent

Performance of holographic gratings, prepared by using epoxy-functionalized siloxane compound as a reactive diluent, was compared with that using N-vinylpyrrolidi none as a diluent in the presence of various contents of liquid crystal under different exposure beam intensity. Siloxane component strongly influenced the kinetics of polymerization, diffusion, and phase separation of the liquid crystalline compound, and high diffraction efficiency was obtained when 3-acryloxypropyltrimethoxysilane or 2-[(3,4-epoxycyclohexyl)ethyl]trimethoxysilane was used as a reactive diluent even at a very low concentration (10-25 wt%) of commercial liquid crystal mixture, E7 (Merk), in contrast to the case with N-vinylpyrrolidinone or benzyl glycidyl ether as the diluent without siloxane component. The phase-separated morphologies of gratings, such as spacing and surface topology, observed by SEM and AFM, were well controlled, and very regular and smooth morphologies were observed for the holographic gratings prepared with 3-acryloxypropyltrimethoxysilane and various contents of the liquid crystal. (c) 2005 Elsevier Ltd. All rights reserved.