High Performance Holographic Polymer Dispersed Liquid Crystal Systems Formed with the Siloxane-containing Derivatives and Their Applications on Electro-optics

Holography is a very powerful technology for high density and fast data storage, which have been applied to the systems known as holographic polymer dispersed liquid crystal (HPDLC), in which gratings are formed by anisotropic distribution of polymer and LC-rich layers through photopolymerization of monomers or oligomers and following phase separation of LC in the form of interference patterns of incident two laser beams [1-5]. Much attentions have been attracted to HPDLC systems due to their unique switching property in electric field to make them applicable to information displays, optical shutters, and information storage media [6-15]. Many research groups have made efforts to realize useful recording materials for high performance holographic gratings [16-18]. Photo-polymerizable materials, typically multifunctional acrylates, epoxy, and thiol-ene derivatives have been mostly studied because of their advantages of optical transparency, large refractive index modulation, low cost, and easy fabrication and modification[19-25]. T.J. Bunning group has reported investigation that the correlation between polymerization kinetics, LC phase separation, and polymer gel point in examining thiol-ene HPDLC formulations to enable more complete understanding of the formation of thiol-ene HPDLCs [26]. Kim group has developed that the doping of conductive fullerene particles to the formulations based on polyurethane acrylate oligomers in order to reduce the droplet coalescence of LC and operating voltage [27]. Further extensive research has been devoted to the organic-inorganic hybrid materials having the sensitivity to visible laser beam to resolve the drawbacks of photopolymerizable materials such as volume shrinkage, low reliability, and poor long term stability even high reactivity of them as well waveguide materials, optical coatings, nonlinear optical materials, and photochromic materials [28-29]. Blaya et al. theoretically and experimentally analyzed the angular selectivity curves of nonuniform gratings recorded in a photopolymerizable silica glass due to its rigidity suppressing the volume shrinkage [30]. Ramos et al. found that a chemical modification of the matrix with tetramethylorthosilicate noticeably attenuates the shrinkage, providing a material with improved stability for permanent data storage applications [31].