Synthesis of titania- and silica-polymer hybrid materials and their application as refractive index-matched layers in touch screens

Titania- and silica-polymer hybrid materials were prepared with an in situ sol-gel process for refractive index-matched, optical thin-film applications. A random copolymer of methyl methacrylate (MMA) and 3-(trimethoxysilyl) propyl methacrylate (MSMA) (poly(MMA-co-MSMA), MMA:MSMA = 78:22 molar ratio) capped with trialkoxysilane in MSMA units was used as a precursor. The precursor was further reacted with titanium (IV) isopropoxide (TTIP) and tetraethyl orthosilicate (TEOS) to synthesize the high (H) and low (L) refractive index hybrid materials, respectively, with an acid-free sol-gel method, which prevents the corrosion of neighboring metals or metal oxides used in optical thin-film applications. The refractive indices of the H and L materials were controlled by the concentrations of TTIP and NaCl used during the acid-free sol-gel process, respectively. The H material on a glass substrate exhibited a high optical transparency of 96%, with respect to bare glass at 550 nm, and a high refractive index of 1.82 when the precursor was reacted with TTIP (90 wt% of the precursor). The L material on a glass substrate showed a high optical transparency of ~100%, with respect to bare glass at 550 nm, and a low refractive index of 1.44 when the precursor was reacted with 2.5 M of NaCl. An indium tin oxide (ITO)/L/H/poly(ethylene terephthalate) thin-film substrate, with the optimum thicknesses of each layer calculated with Macleod software, had a reflexibility difference (ΔR) of < 1% over 65% of the visible spectrum, as well as good flexibility and a long lifetime. These results indicate that the spin-coatable L and H materials could replace the typical low and high refractive index inorganic materials (SiO₂ and Nb₂O₅, respectively) used for flexible touch screen applications.