Silica-based versus silica-titania sol-gel materials - comparison of the physical properties: surface tension, gelation time, refractive index and optical transmittance

Knowledge of the physical parameters and optical constants of sols and sol-gel materials is important in view of their possible applications. In this work, silica and silica-titania sols were examined. Gelation time, surface tension, refractive index and optical transmittance were measured. The sol-gel materials were produced from the silica precursor Si(OC2H5)4 mixed with the titanium dioxide precursor Ti(OC2H5)4 and 96% ethyl alcohol. It was stated that the surface tension of pure silica sols is much higher than in case of silica-titania sols. The refractive index of fresh samples is lower than of stored sols. The transmittance is highest for the fresh samples and it decreases with gelation time; however, this effect is stronger for silica-titania materials. By manipulating with the solvent content and titania addition, the required refractive index may be obtained.