Abstract
This study focuses on manipulating surface wettability from hydrophilic to superhydrophilic or super-liquid repellent in air or oil/water system by using a novel and cost-effective approach. The hierarchically structured surfaces are synthesized by a plasma-assisted nanofabrication method under atmospheric pressure. Due to the fast deposition rate of nanoparticles, a uniformed thin film can be formed on various substrates within a few seconds. After fluorination with perfluoroalkylsilane, it becomes a superhydrophobic and oleophobic surface with good durability. This versatile methodology can even selectively render the surface superhydrophobic by simply blocking area with silicone tapes. Distinguished from the liquid-repellent surfaces in air, the underwater superoleophobic surface can be obtained directly by pre-wetting the as-synthesized structures by water. Owing to the hierarchical structure and large surface area, the entrapped liquid layer is able to avoid the contamination by oils. The critical factors for the membrane used for oil/water separation are also discussed in this research. On the other hand, to further investigate surfaces with dual superlyophobicity in oil/water system by the effect of hierarchically porous structures, which has not been comprehensively studied in literature, a bio-inspired diatomite membrane is synthesized by a freeze casting method. The synergistic effect of sophisticated nano-porous structures of frustules and the micro-channels induces super-liquid repellent property in both oil and water system. This research provides insights for rational designs of a liquid repellent surface either in air or liquids (oils or water), and might further lead to practical applications in self-cleaning, drag reduction and oil/water separation.