| Abstract
| - We report herein the preparation and UV-stimulated wettability conversion of superhydrophobic TiO2 surfaces,as well as the preparation of superhydrophilic−superhydrophobic patterns by use of UV irradiation througha photomask. A CF4 plasma was used to roughen smooth TiO2 sol−gel films to produce a nanocolumnarmorphology, and subsequent hydrophobic modification with octadecylphosphonic acid (ODP) rendered theroughened surfaces superhydrophobic. The superhydrophobic properties of these surfaces were evaluated byboth static and dynamic water contact angle (CA) measurements. It was found that the surface morphologyof the TiO2 film, which was dependent on the etching time, has a great influence on the observedsuperhydrophobic properties. The nanocolumnar surface morphology exhibited large water CA and smallcontact angle hysteresis (CAH); this is discussed in terms of the Wenzel equation and the Cassie−Baxterequation. Under low-intensity UV illumination (1 mW cm-2), the superhydrophobic TiO2 surface underwenta gradual decrease of water CA and finally became superhydrophilic, due to photocatalytic decomposition ofthe ODP monolayer. Readsorption of ODP molecules led to the recovery of the superhydrophobic state. ThisUV-stimulated wettability conversion was employed to prepare superhydrophilic stripes (50 and 500 μmwide) on a superhydrophobic TiO2 surface. The pattern was able to guide water condensation, as well as theevaporation of a polystyrene microsphere suspension, due to the extremely large wettability contrast betweensuperhydrophobic and superhydrophilic areas.
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