Nanoparticle polymer composite volume gratings incorporating chain transfer agents for holography and slow-neutron optics

Abstract

We demonstrate twofold enhancement of the saturated refractive index modulation (Δn(sat)) recorded in a photopolymerizable nanoparticle-acrylate polymer composite film by incorporating thiols acting as chain transfer agents. The chain transfer reaction of thiols with (meth)acrylate monomer reduces the polymer crosslinking density and facilitates the mutual diffusion of nanoparticles and monomer during holographic exposure. These modifications provide increased density modulations of nanoparticles and the formed polymer, resulting in the enhancement of Δn(sat) as high as 1.6×10(-2) at a wavelength of 532 nm. The incorporation of thiols also leads to shrinkage suppression and to improvement of the grating's spatial frequency response. Such simultaneous improvement is very useful for holographic applications in light and neutron optics.

Self-written waveguides in a dry acrylamide/polyvinyl alcohol photopolymer material

“…The resulting gratings have been shown to have good lifetimes [29,30]. If the polymer chains are not cross-linked, they will tend to diffuse out of the exposed regions where they are formed [18,25,35].…”

“…7. A chain transfer agent can be introduced to improve the spatial frequency response [27,28] and counter diffusing nanomaterials, and can be used to reduce shrinkage and increase modulation [29].…”

Characterization of volume holographic recording in photopolymerizable nanoparticle-(thiol-ene) polymer composites at 404 nm

“…This problem of using (meth) acrylate-based NPCs can be relaxed to some extent by the addition of chain-transfer agents by which rapid gelation is delayed and thereby shrinkage can be reduced. 21,22 A different way of mitigating shrinkage may be the use of other polymerization mechanisms that inherently possess lower shrinkage characteristics as compared with the chaingrowth polymerization mechanism. These include cationic ring-opening 23 and step-growth 24 polymerizations.…”

Effects of chain-transferring thiol functionalities on the performance of nanoparticle-polymer composite volume gratings

“…They consist of inorganic nanoparticles (such as TiO 2 , SiO 2 , ZrO 2 , and nanozeolites) that are uniformly dispersed in a host monomer capable of radical-mediated chain-growth photopolymerization [3][4][5][6][7]. Recently, we have demonstrated two-fold enhancement of the saturated refractive index modulation (Δn sat ) of ZrO 2 NPC volume gratings recorded at high spatial frequencies by doping with a single functional thiol (mono-thiol) as a chain transfer agent (CTA) [8]. This result suggested that the incorporation of a CTA in an NPC is very useful for holographic applications of volume gratings in light and neutron optics.…”

“…In the sample preparation we employed the same chemical composition of ZrO 2 NPCs that was used in our previous work [8], except for doped multifunctional thiols having either two or three S-H functional groups. ZrO 2 nanoparticles (the average size of 3 nm) were dispersed at the concentration of 35 vol.% (the optimum concentration that maximizes Δn sat of NPC volume gratings of the same chemical formulation without CTAs) with respect to acrylate monomer, 2-propenoic acid [octahydro-4,7-methano-1H-indene-2,5-diyl)bis(methylene) ester (A-DCP, Shin-Nakamura Chemical Co., Ltd.) [5,8].…”