Controlled contact angle and droplet evaporation using photo-induced hydrophilic surface

Titanium Dioxide, TiO₂, is one of the photocatalysts that has a very unique characteristic. The surface coated with TiO₂ exhibits extremely high affinity for water by exposing the surface to ultraviolet ray and the contact angle decreases nearly to zero. On the contrary, the contact angle increases when the surface is shielded from ultraviolet ray. We have developed two types of TiO₂ surface by sputtering process. One is the copper surface with TiO₂ layer and the other is with TiO ₂ and SiO₂ layer. The contact angle of the former varies between 30-82° and the latter varies between 4-13°. We applied these surfaces to control the contact angles with the other thermal properties of the surface being constant. Experiment of droplet evaporation has been performed to manifest the effect of contact angle on the evaporation curves. It is found that the wetting limit temperature increases as the contact angle decreases to 13°, but it decreases again as the contact angle decreases to 4°.