Controlled preparation of titania nanofilm by a template of polydopamine film and its reversible wettability

Titanium oxide (TiO2) nanofilm was prepared by a simple method of sol-gel deposition on the glass substrate, which was pre-modified with a polydopamine (PDA) film. The as-prepared TiO2 nanofilm was analyzed by X-ray diffraction, scanning electron microscopy, and atomic force microscopy. The thickness of TiO2 film can be controlled by the thickness of PDA film, which was dependent on the polymerization time. The mechanism of wettability conversion on TiO2 film was investigated by means of contact angle measurements in different experimental conditions. The results demonstrated that humidity was the major factor for converting the hydrophobic surface of TiO2 film into hydrophilic surface under ultra-violet (UV) irradiation. And atmospheric oxygen played dominant role in reconverting the hydrophilic surface of TiO2 film into hydrophobic surface when it was stored in the dark. The TiO2 nanofilm showed reversible hydrophobic/hydrophilic conversion in the condition of alternating between UV irradiation and storage in the dark.