Surface charges of oxides and wettability: Application to TiO2–SiO2 composite films

The super-hydrophilicity which can exist at the interface between oxides and aqueous solutions is able to sustain industrial and domestic applications. Several experimental results obtained on TiO2–SiO2 composite thin films via a sol–gel route have confirmed a natural and persistent super hydrophilicity under standard atmosphere. This property can be easily photo-regenerated after a long aging period in ambient atmosphere using a short UV illumination. The electrochemical double layer which classically exists between oxide surfaces and aqueous solution is unfavorable to high wettability properties of ideal flat surfaces. The present study indicates how the surface rugosity and the disjoining pressure caused by surface charges are able to explain the stability of a prewetting film. This film can withstand to vaporization in a weakly under saturated atmosphere, having a protective action despite a carbon contamination brought by standard atmosphere.