Relationship between the structure and water repellency of nickel-cobalt alloy coatings prepared by electrodeposition process

The combination of suitable hierarchical structure and low surface energy plays a vital role in fabricating superhydrophobic coatings on hydrophilic metal substrates. The present study introduces a highly anti-corrosion and self-cleaning super-hydrophobic Ni-Co alloy coating fabricated by electrodeposition process. Based on the structures grown at various process parameters, different morphologies including nano-cones and flower-like were obtained. The relation between surface morphologies and wettability behavior was investigated in detail. The surface of Ni-Co coatings freshly grown on copper substrate was super-hydrophilic with water contact angle below 10 degrees. However, without further processing, the wettability transited from super-hydrophilic nature to a super-hydrophobic one by passing time under ambient condition. The results showed that when the deposition current density falls in the range 20-30 mA cm(-2) with times longer than 600 s, the water contact angle on the Ni-Co coating was as high as 160 degrees, and sliding angle was ultra-low (below 5 degrees). A detailed XPS analysis indicated that this wettability transition was mainly caused by adsorption of airborne hydrocarbons onto the coating surface. The potentiodynamic polarization curves revealed that the super-hydrophobic film has considerably improved the corrosion performance of the Ni-Co alloy coating. Moreover, the super-hydrophobic surface showed a strong self-cleaning property. (C) 2015 Elsevier B.V. All rights reserved.