Thickness effects in naturally superhydrophilic TiO2–SiO2 nanocomposite films deposited via a multilayer sol–gel route

TiO2–SiO2 nanocomposite films of various thicknesses have been deposited via a multilayer sol–gel route. These films exhibit a natural and persistent superhydrophilicity, which allows considering new applications for easy to clean surfaces. Atomic force microscopy, scanning and transmission electron microscopy, as well as ellipsometry and UV/visible spectrometry measurements, were performed to study how the multilayer procedure influenced the morphology and composition of composite films in relation to their thickness. The natural and photo-induced wettability of these films was studied and discussed in relation to morphology, composition, and thickness features. It is concluded that, while such features did not significantly influence the natural wettability of nanocomposite films, their photo-induced wettability was considerably enhanced when increasing their thickness, which favored a faster superhydrophilicity photo-regeneration when this natural property started to disappear after a long aging period in ambient atmosphere.