Cu surfaces with controlled structures: From intrinsically hydrophilic to apparently superhydrophobic

A series of Cu films with different surface structures were fabricated by an improved electric brush-plating technique. In the absence of surface chemical modification, the Cu films exhibited hydrophobic and even superhydrophobic behaviors due to their three-level hierarchical structures. Based on the classical Wenzel and Cassie models, the effects of two dimensionless geometrical parameters (the aspect ratio and the spacing factor of micro-scale structure) on the wetting behaviors of the Cu films were investigated. It was demonstrated that to obtain the stable Cassie superhydrophobic state, the aspect ratio and the water contact angle on the basal surface should be as large as possible and the spacing factor should be limited within a specific range for given aspect ratio and water contact angle on the basal surface.