Stoichiometric thiol-to-ene ratio dependences of refractive index modulation and shrinkage of volume gratings recorded in photopolymerizable nanoparticle-polymer composites based onstep-growth polymerization

Spectroscopic, photocalorimetric and holographic measurements are conducted to investigate effects of stoichiometric thiol-to-ene ratio on the polymerization dynamics, refractive index modulation, recording sensitivity and polymerization shrinkage of volume gratings recorded in silica nanoparticle-polymer composite films based on step-growth radical addition polymerization. It is found that the polymerization rate of the composite system is maximized at the stoichiometric thiol-ene composition. It is also found that while the refractive index modulation and the recording sensitivity are maximized at the stoichiometric thiol-ene composition, polymerization shrinkage decreases with increasing the thiol monomer fraction. A negative correlation between gel point conversion and shrinkage is observed.