Molecular composites comprising TiO2 and their optical properties

An in situ synthesis to form an organic-inorganic hybrid film with tunable optical properties is described. The nanocomposite comprises a titania nanophase that is formed from titanium alkoxide in the presence of a matrix polymer. XPS study indicates that titanium (Ti) in the nanophase is fully oxidized to Ti(IV), similar to that in TiO2. When a random copolymer, of styrene and 3-methacryloxypropyltrimethoxysilane (MPTMS), comprising functional groups that form a covalent bond with the in situ synthesized TiO2 is used, TEM and AFM show no phase contrast between the organic and inorganic phases at the nanometer level. This suggests a molecular level mixing of the polymer and formed inorganics and thus the formation of a molecular composite. This synthesis generates transparent composite films with any level of incorporation of TiO2. The refractive indices of these molecular composite films are much higher than that predicted on the basis of effective medium theories; e.g., at a TiO2 loading of 27 vol %, the resulting molecular composite film exhibits a measured refractive index of 1.76 compared to that of 1.66 predicted by effective medium theories.