UV-Curable Polymer Nanocomposites Based on Poly(dimethylsiloxane) and Zirconia Nanoparticles: Reactive versus Passive Nanofillers

As the need for high-refractive-index materials escalates to meet the growing demands for antireflective coatings and various photonic devices with robust mechanical properties, elastomeric polymer nanocomposites containing a high loading level of zirconia nanoparticles afford tremendous promise. In this study, the interactions between two functionalized zirconia nanoparticles, one reactive and the other passive, with a short-chain, UV-curable poly(dimethylsiloxane) in solvent are systematically examined by dynamic rheology. The effects of surface functionality, as well as UV light intensity and nanoparticle loading, on the cross-linking behavior are elucidated, and both filled systems are observed to form cross-linked networks at loading levels of up to 85 wt % zirconia. The time required to achieve dynamic modulus crossover (indicating network formation) exhibits a power-law dependence on the UV light intensity for both systems at all zirconia contents. At high loading levels of the passive nanofiller (75 wt % zirconia), the resulting films appear opaque, possessing significantly higher turbidity than those containing reactive nanoparticles, which conversely yield films with low turbidity and high optical clarity at loading levels as high as 80 wt % zirconia. Reactive zirconia is more strongly incorporated into the polymer network than passive zirconia, as evidenced by values of the ultimate gel moduli, zirconia leaching from solvent-swelled films, and the topologies of cross-fractured surfaces.