Holographic nanoparticle-polymer composites based on step-growth thiol-ene photopolymerization

We report on the photopolymerization kinetics and volume holographic recording characteristics of silica nanoparticle-polymer composites using thiol-ene monomers capable of step-growth polymerization. Real-time Fourier transform spectroscopy and photocalorimetry are used to characterize the visible light curing kinetics of a thiol-ene monomer system consisting of secondary dithiol with high self-life stability and low odor and triene with rigid structure and high electron density. It is shown that while the nanoparticle-(thiol-ene) polymer composites exhibit high transparency, their saturated refractive index modulation (Delta n(sat)) and material sensitivity (S) are as large as 1x10(-2) and 1615 cm/J, respectively. The polymerization shrinkage is reduced as low as 0.4% as a result of the late gelation in conversion. These values meet the acceptable values for holographic data storage media (i.e., 5x10(-3), 500 cm/J and 0.5% for Delta n(sat), S and shrinkage, respectively). It is also shown that because of the dispersion of inorganic silica nanoparticles and the use of the triene monomer having the rigid structure of the triazine functional group, the thermal stability of recorded holograms is much improved over our previously reported nanoparticle-polymer composites using organic nanoparticles and primary mercaptopropionate trithiol/allyl ether triene monomers [Opt. Lett. 35, 396 (2010)]. (C) 2011 Optical Society of America