Photopolymerization of TiO2-based hybrid materials: effect of nanoparticles loading and photosensitive 1D microstructures fabrication

International audience ; Hybrid materials, based on inorganic nanoblocks incorporated into polymer networks, are an important class of functional materials. Although the kinetic of the free-radical polymerization of neat polymers has been studied for many years, both theoretically and experimentally, studies devoted to the polymerization kinetics of nanocomposite materials are rare. In this study, photosensitive hybrids formed using poly(2-hydroxyethyl methacrylate) (pHEMA) and titanium dioxide (TiO2) nanoparticles functionalized with polymerizable ligands were considered. Their bulk UV-induced free-radical photopolymerization was investigated to evaluate the potential of pHEMA/TiO2 hybrids as a material of choice for the fabrication of micro-optical devices. The influence of the nanoparticle concentration and UV intensity on the polymerization kinetics, probed in situ by Raman spectroscopy, is discussed. A decrease in the initiation rate was observed, which was attributed to the UV absorption of TiO2 nanoparticles. This leads to a decrease in the propagation rate with an increase in nanoparticle concentration. Furthermore, a decrease in the maximum C=C conversion yield was observed when the nanoparticle concentration was increased. This was attributed to the formation of microgel regions around the nanoparticles, which prevented the polymer chains from bonding with surface ligands. Despite the lower conversion yield, we demonstrated the fabrication of one-dimension (1D) photoactive microstructures in pHEMA/TiO2 hybrids. The photochromic efficiency of the obtained structure was evaluated based on the reduction in silver (Ag) ions under UV irradiation. The results show that pHEMA/TiO2 hybrids can be considered as a prospective material for the realization of photosensitive microelements.