Effect of zeolite nanoparticles on the optical properties of diacetone acrylamide-based photopolymer

The effect of zeolite nanoparticles with BEA type framework structure on the optical properties of a diacetone acrylamide (DA)-based holographic photopolymer has been investigated. Both types of zeolite nanocrystals, as synthesized (BEA) and silver containing (BEA-Ag), are used for doping the DA photopolymer. Doping of the DA photopolymer with BEA zeolites results in an 11% decrease of the average refractive index of the nanocomposite layer, while the inclusion of BEA-Ag nanoparticles decreases the average refractive index by 3% only. This observation is in good agreement with the fact that the contrast in refractive index between the host photopolymer and nanoparticles is expected to be much lower for the BEA nanoparticles containing Ag in their pores. Doping of the DA photopolymer with pure BEA zeolite nanoparticles results in a significant increase in refractive index modulation due to holographic recording, Delta n, of up to 91% at a concentration of 2 wt.% compared to un-doped layers. For the BEA-Ag zeolites, a maximum increase in Delta n of up to 17% at a concentration of 0.5 wt.% is observed. The increase in Delta n is attributed to the difference in n between the host photopolymer and nanoparticles and the redistribution of the nanoparticles during holographic recording. It is demonstrated that the DA photopolymer is compatible as a host material for the porous BEA nanoparticles. This is due to the large size of the DA monomer molecules, which restricts monomer migration into the zeolite pores and thus the pores of the Ag-free BEA nanoparticles remain empty, making them suitable for application in holographic sensors. (C) 2014 Elsevier B.V. All rights reserved.