Rapid Reversible Superhydrophobicity to Superhydrophilicity Conversion of HF-Tuned ZnO Flower-Like Micro-Sphere Films
Superhydrophobic ZnO films were prepared by a simple low-temperature solution method, where the ZnO morphology was tuned by hydrofluoric acid. The film topography presents two different length scales: micro flower-like-spheres and nano petals. Such hierarchical structures give the film a superhydrophobic behavior with water contact angle (CA) of 151°, turning into a superhydrophilic one (CA < 5°) after 30 min vacuum ultraviolet (VUV) illumination. The transition from superhydrophobicity to superhydrophilicity is more quickly than the past report using UV illumination because VUV gives higher energy upon the ZnO films. The VUV-illuminated film can be recovered to superhydrophobic through being placed in the dark. Such special wettability can be explained based on ZnO as a photoinduced semiconductor and a photocatalyst. This study will greatly extend applications of ZnO nanomaterials to many important fields, such as microfluidic devices.
Wei Pan and Jianghong Gong
C. S. Liu et al., "Rapid Reversible Superhydrophobicity to Superhydrophilicity Conversion of HF-Tuned ZnO Flower-Like Micro-Sphere Films", Key Engineering Materials, Vols. 368-372, pp. 1374-1376, 2008