The study of photo-polymerization kinetics of methylmethacrylate initiated by the quantum dots of cadmium sulfide

Media containing quantum dots (QDots) of semiconductor AIIBVI groups are unique materials whose optical properties depend on the size and shape of the nanoparticles. QDots of such materials are widely used: fluorescent labels, bio and chemical sensors, luminescent solar concentrators, layers of active elements of solar cells and other practical interest composites consisting of acrylic polymers and QDots. A promising approach is the synthesis of quantum dots directly into the environment and following polymerization of the monomer in the block composites. Under photopolymerization of CdS / MMA the size and properties of QDots change. Nanoparticles affect the polymerization process, too. To create composites of CdS / PMMA QDots with desired properties it is important to know the mechanisms of the processes occurring during the synthesis and to be able to manage them. In this paper we study the effect of size, particle concentration and irradiation parameters on the kinetics of photopolymerization medium. The dynamics of changes in the size and properties of CdS nanoparticles with different concentrations and ratios of precursor components under photopolymerization of CdS / MMA colloids were investigated. To study the changes in the characteristics of nanoparticles in colloidal solutions of CdS / MMA and mechanisms of the photopolymerization process, three samples were synthesized with different average particle size. To do this, at a fixed concentration of the precursor (CF₃COO)₂Cd we varied the concentration of the precipitant H2S. During the experiment at different doses of colloidal solutions of QDots of CdS / MMA, the conversion of MMA in PMMA, the concentration and size of nanoparticles were determined and the absorption spectra were recorded. Investigation of the processes occurring during irradiation of colloidal solutions of QDots of CdS / MMA made it possible to establish the following regularities and draw conclusions: l. At the initial stage of irradiation (20 minutes) the rate of polymer formation is low (induction phase). During this time the CdS particles effectively absorb a considerable amount of photons, which leads to the generation of electrons (e) and holes (h+) on their surface. At the same time, the charge stock from the particles to MMA and the recombination of electrons and holes are small, which leads to thermodynamic instability. In the medium the processes of photocorrosion and photodegradation occur efficiently, which reduces the average size and increases the number of particles per volume unit. 2. The speed of photopolymerization under irradiation of colloidal solutions of QDots of CdS / MMA does not correlate with the number of particles, but with the surface area of cadmium sulfide nanoparticles in the monomer. 3. The features of photopolymerization flow and dimensional change of QDots under irradiation of different samples of colloidal solutions of QDots of CdS / MMA are connected with the amount and nature of nanoparticle defects (depending on the ratio of sulfur / cadmium used in the synthesis of nanoparticles). The results will be used in the synthesis of polymeric composite materials for multilayer luminescent solar concentrators (LSC) and other fluorescent optical converters.

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