The Novel Wetting Behavior of Periodic TixSn11xO2 Nanostructures

Regular arrays of TixSn11xO2 nanostructures were produced through glancing angle sputter deposition onto self-assembled close-packed arrays of 200-nm-diameter and 1-μm-diameter polystyrene microspheres respectively. The anisotropic nanoflakes grown on 200-nm-diameter polystyrene microspheres exhibited macroscopic-wetting anisotropy, with the apparent contact angle observed parallel to the direction of the nanoflakes larger than the apparent contact angle in the perpendicular direction. This anisotropic wettability is ascribed to the difference of the three-phase contact line structure for the parallel and perpendicular direction, resulting from the anisotropic topography. Compared with the nanoflakes, the “spheric shells” were obtained using the 1-μm-diameter polystyrene microsphere templates, on which the apparent contact angle of the drop was nearly uniform along the contact line. After annealing at 823K for 3 h, both the films were crystallized to TiO2/SnO2 composite and maintained good thermal stability in the morphology. It was shown that the “spheric shells” can be reversibly switched between hydrophobicity and superhydrophilicity by alternating visible light illumination and dark storage. This novel visible light-responsive behavior was explained by the enhanced separation efficiency of photogenerated electron­hole pairs in the TiO2/SnO2 composite. [doi:10.2320/matertrans.M2011269]