Synthesis of Polymeric Nanocomposite Hydrogels Containing the Pendant ZnS Nanoparticles: Approach to Higher Refractive Index Optical Polymeric Nanocomposites

Nanocomposites have attracted more attention due to their extensive applications. However, it is still a huge technological challenge in fabrication of transparent hybrid materials because of nanoparticle aggregation resulting from their high specific surface energies. In this paper polymerizable molecule was controlled chemically grafted onto ZnS nanoparticles to obtain polymerizable-group-capped nanoparticles that can copolymerize with a mixture of acrylic monomers of N,N-dimethylacrylamide (DMA) and 2-hydroxyethyl methacrylate (HEMA) or glycidyl methacrylate (GMA) or methyl methacrylate (MMA) to prepare transparent high refractive index (RI) nanocomposite hydrogels. The dispersion homogeneity of the nanoparticles in the nanocomposites was studied by dynamic mechanical thermal analysis (DTMA), transmission electron microscopy (TEM), scanning electron microscopy (SEM), and energy dispersive X-ray mapping analysis (EDX). Moreover, the nanocomposites were characterized by transmittance, mechanical properties, and refractive index (RI). The results showed that grafted amount of polymerizable group on the nanoparticle surface influences the cross-link density and microphase structure of the resultant nanocomposites, leading to different transmittance and mechanical properties. The RI of hydrated and dry nanocomposites can be regulated to a peak value of 1.652 and 1.751, respectively, by a simple adjustment of ZnS content in the nanocomposites. Our approach was also proved to be effective in preparing DMA-free transparent nanocomposites with high RI of 1.824 by copolymerizing between polymerizable-group-capped ZnS and single monomer of HEMA or GMA or MMA.