Holographic nanoparticle-polymer composites based on radical-mediated thiol-yne photopolymerizations: characterization and shift-multiplexed holographic digital data page storage

Abstract

We investigate volume holographic recording in a photopolymerizable nanoparticle-polymer (NPC) composite film that employs radical-mediated thiol-yne step-growth photopolymerizations. Because each alkyne functional group can react consecutively with two thiol functional groups in thiol-yne photopolymerizatins, the thiol-yne based NPC system dispersed with inorganic nanoparticles has the potentiality to overcome the drawback of low crosslinking densities but to retain the advantage of low shrinkage that is possible by use of thiol-ene photopolymerizations. We show that a thiol-yne based NPC film dispersed with 25 vol.% SiO2 nanoparticles and 15 wt.% single functional co-monomer gives the saturated refractive index change as large as 0.008 and the material recording sensitivity as high as 2005 cm/J at a recording and readout wavelength of 532 nm. We find that while the shrinkage of a volume hologram recorded in a thiol-yne based NPC dispersed with organic nanopartices can be as low as 0.5%, it is approximately 1% with the dispersion of SiO2 nanoparticles due to the plasticizing effect of the doped co-monomer. On the other hand, the thermal stability is improved better with the dispersion of SiO2 nanoparticles. We also demonstrate shift-multiplexed holographic storage of 80 digital data pages in a thiol-yne based NPC film with high readout fidelity.