Patterned hydrothermal synthesis of TiO_2 to produce droplet repelling forces

摘要

Hydrophilic/hydrophobic pattern on a surface repels water droplet because a driving force acts on the droplet from hydrophobic area to hydrophilic area due to the imbalance of surface tensions. In the case of oil droplet in water, the driving force acts oppositely due to the same reason. These driving forces can be applied to produce a self-cleaning function. The forces can be enhanced with tapered wettability pattern on the surface. To extend the functional life, this study applied the patterned hydrothermal synthesis of TiO_2 for hydrophilic area because its hydrophilicity can be ensured by photocatalytic activity with UV irradiation. Hydrothermal synthesis on a fluoride-doped tin oxide (FTO) substrate produces an array of TiO_2 vertical rods. By masking the hydrothermal synthesis with star-like patterned photomasks, TiO_2 rods were successfully synthesized leaving hydrophobic star-like areas. A star-like pattern has four tapers to gather the spread thin oil film to make a droplet. After observing the morphology of the structure, oil droplet repelling performance was examined. It was found that the sliding angle of oil droplet in water drastically decreased with the help of patterned structure. The effect of UV irradiation dose on the repelling performance was also made clear.