High-refractive-index polymer/inorganic hybrid films containing high TiO2 contents

In this study we used a low film-forming temperature to fabricate high-refractive-index polymer/TiO2 hybrid films featuring high TiO2 contents. We incorporated pre-made TiO2 nanoparticles (NPs) into titanium alkoxide and/or epoxy resin at various NP contents and then investigated the effects of the relative proportions of TiO2 NPs, titanium alkoxide, and epoxy resin on the refractive indices. The variation of the refractive index was examined in terms of the morphologies and compositions of the hybrid films. The maximum values of the refractive indices of the hybrid films occurred at high TiO2 NP contents, but not at pure TiO2 NP contents. Microstructural images suggested that this phenomenon occurred because of the presence of spaces existing between the NPs as a result of our use of an ex situ synthesis method. The maximum values of the refractive indices of the hybrid films featuring a matrix comprising both titanium alkoxide and epoxy resins were larger than those obtained when the matrix was either titanium alkoxide or epoxy resin alone; indeed, the refractive index of a titanium alkoxide/epoxy/TiO2 hybrid film reached as high as 1.972—close to that of a pure anatase titania thin film fabricated at high temperature.