Achieving of bionic super-hydrophobicity by electrodepositing nano-Ni-pyramids on the picosecond laser-ablated micro-Cu-cone surface

The fabrication of a bionic super-hydrophobic metallic surface without any low-surface-energy modification is investigated, in which picosecond laser ablation, electropolishing and electrodeposition are used sequentially. The micro-cone structure is formed via laser ablation, and then the nano-pyramid structure is electrodeposited on the micro-cone structure, resulting in a hierarchical structure that is important for achieving super-hydrophobicity on an intrinsically hydrophilic material surface. In this study, the surface morphology and material removal mechanism are discussed with respect to the laser-ablated surface and the subsequent electropolished/electrodeposited surfaces. The condensation experiments results show that both types of surfaces are associated with relatively high contact angles (CAs) at normal temperatures, and the CAs are 147 degrees and 160 degrees, respectively. However, the CA on the laser-ablated surfaces at low temperatures decreases to as less as 107 degrees, which may be owing to the easy transition from Cassie state to a metastable state or even the Wenzel state, leading to a degraded hydrophobic surface. By contrast, the CA on the sequentially processed surfaces still maintains at 150 degrees, which should be attributed to the densely distributed nano-scale structures. The sequentially processed surfaces also show excellent long-term durability. Furthermore, this technique has been employed for fabricating super-hydrophobic surfaces with CM > 151 degrees and the sliding angles (SAs) < 8 degrees on the inclined surfaces with the inclination angle alpha < 30 degrees. Overall, the technique presented in this study supply a practical and reliable method for realizing the stable Cassie state and hence super-hydrophobicity on metallic surfaces.