Facile Route Toward Mechanically Stable Superhydrophobic Copper Using Oxidation-Reduction Induced Morphology Changes

We present that the morphological change induced by an oxidation reduction reaction can be effectively employed for easily producing superhydrophobic copper without any use of hydrophobic agents. By thermal oxidation of copper, needle-shaped copper oxide nanowires (NWs) were grown on the copper substrate. Subsequent reduction led to wavy copper NW structures, which exhibited superhydrophobic properties (contact angle of over 160 degrees and sliding angle of less than 2 degrees). We found that the water adhesion behavior on a surface could markedly vary with the shape of miniature structures of the surface, presumably due to the pinning effect. Microstructure, element, and surface analyses indicated that the outermost layer (similar to angstrom) of the resulting copper NW's is mainly composed of Cu2O. Furthermore, the resulting superhydrophobic copper structures were observed to have good mechanical stability as well as chemical stability. This simple and scalable method could potentially be adopted in industry or academia where research on anticorrosion, antibiofouling, or drag reduction of copper-based objects is performed.