Fabrication of a Pure TiO₂ Thin Film Using a Self-Polymeric Titania Nano-Sol and Its Properties

A pure TiO₂ thin film without adding any organic binder was fabricated by using a self-polymeric titania nano-sol (14 mass%), which was prepared by the acid peptization method. The particle size distribution in the 14 mass% TiO₂ sol, in which almost of particles had a size below 10.2 nm and the crystal phase confirmed by X-ray diffraction analysis was anatase. The diluted nano-sol had a capability to form a thin film at a low temperature (100–400 °C) on the slide glass by dipping method. The average thickness of a coating film was measured to be about 0.25–0.30 μm. A coated film had a high refractive index over 1.88 at least irrespective of the heat-treatment even at room temperature drying and showed a super-hydrophilicity (< 5°) after 20 minutes under Ultra Violet light irradiation, and it sustained in the darkness during a long period over 7 days depending on the heat-treatment conditions. Atomic Force Microscopic observation shows that the morphology of a heat-treated film had a relationship with the long-term hydrophilicity in the darkness.