Wettability and formation mechanism of ZnO micro-spheres composed film

This paper reports that the film composed of flower-like ZnO micro-spheres, which consists of nano-sheets, is fabricated by chemical bath deposition. By adding hydrogen fluoride (HF) into the reaction solution, which contains zinc nitrate hexahydrate and hexamethylenetetramine, the ZnO crystal growth process is changed and the film composed by ZnO micro-spheres is obtained after keeping the reaction solution at 95 ^\circC for 2 h. The morphology, crystal phase and wettability of the sample are characterized by scanning electron microscope, x-ray diffraction and contact angle meter, respectively. The results show that the film has the micro-nano compound structure. After modification with heptadecafluorodecyltrimethoxy-silane, the wettability of the film changed from superhydrophilicity to superhydrophobicity, on which water contact angle and the sliding angle are 154^\circ and less than 5^\circ for 8-μL water droplet, respectively. Additionally, the formation mechanism of the ZnO micro-sphere is also discussed.