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Theoretical calculations suggest that creating superoleophobic surfaces would require a surface energy lower than that of any known materials. In the present work, we demonstrate micronanostructured ZnO-based surfaces displaying apparent contact angles (CA) greater than 150, even with hexadecane (surface tension l = 27.5 mN/m). The specific ZnO microtextures were fabricated by a chemical solution method, and fluoroalkylsilane (FAS) was then used to tune the surface wettability. The combination of ZnO microtextures and FAS modification resulted in a superoleophobicity with CA for hexadecane was 154.6 (161.9 for diethylene glycol (l = 45.2 mN/m). This apparent superoleophobic behavior was induced on intrinsically oleophilic materials mainly by topography (i.e. the specific ZnO microtextures), which form a composite surface of air and solid with oil drop sitting partially on air. Such special wetting state is a metastable Cassie state. The results are expected to promote the study on self-cleaning applications, especially in the condition with oil contaminations.

Superhydrophobic surfaces, which have anti-adhesion and self-cleaning properties, were fabricated on Al substrates. The self-cleaning surface was prepared by two steps: firstly, a chemical solution method was used to create the surface roughness with disorderly veins micronanostructures. Secondly, fluoroalkylsilane was deposited on the rough surface to lower its surface energy. The combination of veins micronanostructures and fluoroalkylsilane modification gave the surface a superhydrophobicity with static water contact angle of 166° and sliding angle of smaller than 1°. Additionally, the surface showed a strong anti-adhesion with water and a satisfied self-cleaning property. Water droplets easily rolled off the surface and picked up dirt and debris with them. The surfaces obviously corresponded to Cassie (not Wenzel) -model. Air entrapped within the veins microstructures greatly increases the air/water interface, effectively preventing the penetration of water into the grooves, and finally exhibiting the self-cleaning property. The results will greatly extend Al substrates for specific functions such as water-repellence, self-cleaning and anti-fouling.

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.