G. Berthomé

Morphology-wettability relations in artificially structured superhydrophilic TiO2–SiO2 composite films

Naturally superhydrophilic TiO2–SiO2 composite films were deposited through a sol–gel route and the morphology of these films was artificially modified by nanosphere lithography using polystyrene spheres. Morphology changes induced by this structuration were studied by optical, scanning electron, and atomic force microscopy. The water wettability of the so-obtained films over aging under ambient atmosphere was then studied with respect to the sol composition and morphological features. This study i/confirms the assumption of a natural superhydrophilicity of composite films intrinsically induced by TiO2–SiO2 granular interfaces and ii/shows that this property can be greatly improved by artificially induced morphology features. Such features are discussed on the basis of well-established surface thermodynamic models.

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.