Physico-chemical role of CdSe/ZnS quantum dots in the photo-polymerization process of acrylate composite materials

Abstract

The work presented in this paper is devoted to the physico-chemical role of quantum dots (QDs) in the photopolymerization of composite materials. We show first that the photoexcitation of CdSe/ZnS semiconductor quantum dots can initiate the polymerization of an acrylate monomer in association with a tertiary amine and in the absence of a photoinitiator. But by using a holographic technique, among the others, the gratings recorded in such composite materials are not stable and relax once the light interference pattern is switched off. This behaviour is attributed to a very low degree of conversion of monomers, which does not prevent the post-exposure diffusion of monomers and nanoparticles. The comparison with gratings obtained in the presence of a photosensitizer dye (higher hologram quality and stability) highlights the key importance of using such dye in the polymerization process. The gratings recorded in the complete syrup, containing the dye and QDs which differ by their size and UV-visible absorption spectra, exhibit an additional refractive index modulation. The latter results from the spatial distribution of QDs and the change in the kinetics of polymerization. We further focus on understanding the fall of the polymerization rate owing to the presence of QDs. This decrease may result from the trapping of the tertiary amine (co-initiator) at the surface of those QDs, which reduces the rate of decay of the dye and, consequently, the polymerization rate. Under such conditions, the diffusion of QDs and monomers is favoured and their spatial redistribution is enhanced. These features contribute to modify the physical properties of the gratings.

Photopolymerizable nanocomposite photonic materials and their holographic applications in light and neutron optics

“…On the other hand, CdZnS (4–7 nm in diameter) having a moderate quantum yield was able to be dispersed at the concentration of 20 wt% with appropriate reagents. Barichard et al [ 63 , 64 ] also investigated the photopolymerization process and volume holographic recording at 488 nm in NPCs incorporating CdSe/ZnS QDs (5.2 nm in diameter). It was found that the presence of QDs gave a noticeable decrease in the polymerization rate due to the trap of a co-initiator at the surface of QDs, facilitating the diffusion of monomer and QDs under inhomogeneous light illumination and thereby increasing to as large as at 0.5 wt% CdSe/ZnS QDs.…”

“…Following their demonstration, holographic recording in NPCs employing various types of inorganic nanoparticles has also been reported so far at visible and near-ultraviolet recording wavelengths. These include inorganic nanoparticles ( , SiO , , , , , nanozeolites, semiconductor quantum dots (QDs)) [ 37 – 64 ] and organic nanoparticles [ 65 ]. It was found that, as opposed to Oliveira et al’s case [ 18 ], monomer molecules (neutral nanoparticles) generally diffuse from the dark (bright) to the bright (dark) regions under holographic exposure due to the mutual diffusion of monomer and nanoparticles [ 66 – 69 ].…”

Effects of ZnO quantum dots on the photostability of acrylate photopolymers used as recording materials

“…However, in order to develop photosensitive materials with advanced performance (higher ∆n), the research was oriented towards phototopolymers doped with dispersed nanoparticles during the last decades. Scientists displayed lots of imagination in investigating this approach; thus TiO 2 [3][4][5][6], SiO 2 [6][7][8][9][10], ZrO 2 [6,[11][12][13], ZrO 2 :Eu 3+ [14], LaPO 4 :Ce 3+ , Tb 3+ [15], LaPO 4 :Tb 3+ nanorods [16], silver [17,18] and gold nanoparticles [19], CdSe [20], CdSe/ZnS [21,22] and ZnO quantum dots (QDs) [23] were used more or less successfully. During the course of the recording process, nanoparticles were forced to diffuse away from the constructive to the destructive interference regions of the interference pattern [7,11,[15][16][17][18][19]21,24].…”

Современное Состояние Разработки Светочувствительных Сред Для Голографии (Обзор)

“…Фо-тоиндуцированное изменение показателя преломления составляло n = 1 · 10 −2 при экспозиции 15 mJ/cm 2 [76]. В качестве наночастиц использовались квантовые точки CdSe/ZnS [77].…”