Imaging of Hydrophilicity and its Inhomogeneity on a Titanium Dioxide Film Exposed to Ultraviolet Irradiation Using a Newly Developed Near-Infrared Camera

Abstract

This study has investigated hydrophilicity changes and their inhomogeneity of TiO₂ films on Pyrex glasses by near-infrared (NIR) spectral imaging. Near-infrared spectra of TiO₂ films in the 9000–4000 cm⁻¹ region were measured using a newly developed NIR camera named Compovision. A band in the 5400–4800 cm⁻¹ region, which is assigned to a combination (v₂ + v₃) mode of bending (v₂) and antisymmetric stretching (v₃) modes of the H₂O molecule, was clearly identified and its intensity increased with time in the air. It is interesting that the increased rate rose with ultraviolet (UV) light irradiation (300–400 nm, 1 mW cm⁻²) compared to without UV light irradiation. This result suggested that the hydrophilicity of TiO₂ was enhanced about twice upon the UV light irradiation. Moreover, the NIR images clarified spatial distributions of the hydrophilicity on the TiO₂ surface with a significantly wide area (20 × 40 mm) and a high speed (within 5 s for one image). This rapid imaging system enabled us to detect the hydrophilicity change during only 1 min. The potential of this camera is quite superior, not only for basic research, but also for diverse industrial applications.