Wettability control of photocatalytic crystal layers by hydrophobic coating and subsequent UV light irradiation

Wettability of solid surfaces with water is governed by surface morphology and composition. In this study, a surface finishing technique consisting of three processes, that is, nanotexturing by nanosized photocatalytic crystal coating, hydrophobic coating by chemical vapor deposition and subsequent ultraviolet light photolithography, was employed to form ultrahydrophobic/ultrahydrophilic solid surfaces. Flux grown nanosized K4Nb6O17 crystals were selected as a photocatalyst. A proper nanotexure of crystal layer surfaces enhanced their hydrophobicity. The rough solid surfaces modified by alkyl- and fluoro-alkyl silane were converted from ultrahydrophobic (> 150°) to ultrahydrophilic (< 10°) by photocatalytic oxidation using the K4Nb6O17 crystal layer. Fine pitch ultrahydrophobic/ultrahydrophilic patterns were readily obtained by photocatalytic lithography by use of area-selective 254 nm-ultraviolet light irradiation.