Hydrophobic anatase TiO2-based thin films modified with Al, Cr derivatives to reach reversible wettability control

Abstract

Polycrystalline anatase TiO₂-based thin films with surface roughness were fabricated using a sublimation method. Their surfaces showed hydrophobicity with a water contact angle (CA) higher than 130° when stored in the dark. For the films, the hydrophobic conversion behavior and critical CA depended on surface morphologies. The higher hydrophobic conversion rate and higher critical CA were explained by the smaller r in the Wenzel equation and the smaller f (f = 0.56, 0.30) in the Cassie equation, respectively. Moreover, good reversibility between hydrophobicity (CA = 130°) and high hydrophilicity (CA = 0°) was observed by alternating between UV light irradiation and dark storage. The combination of chromium oxide with anatase TiO₂ markedly shortens the period of hydrophobic conversion from 12 to 5 days.