Super-hydrophobic nickel-cobalt alloy coating with micro-nano flower-like structure

A simple electrodeposition process was proposed to fabricate super-hydrophobic nickel-cobalt alloy coating without modification by low free energy materials. In this paper, the correlation between wettability and surface characteristics has been investigated. Scanning electron microscopy (SEM), X-ray photoelectron spectroscopy (XPS), confocal profilometry and optical tension measurements were used to characterize the micro-structure and wettability properties of the coatings. The results showed that surface morphology, surface roughness and surface energy play critical roles for the wettability of the coatings. The surface of freshly prepared Ni-Co alloy coatings was highly hydrophilic with a water contact angle of 0 degrees. Meanwhile, after being exposed to air for two weeks, surface of the coatings fabricated by one and two electrodeposition steps became super-hydrophobic with water contact angles of 158 degrees and 163 degrees, respectively. This phenomenon was attributed to micro-nano flower-like structure of Ni-Co coating as well as adsorption of airborne hydrocarbon adsorbates on coating surface. The super-hydrophobic Ni-Co coatings possessed good chemical stability and long term durability. Moreover, the super-hydrophobic surfaces possessed self-cleaning properties. (C) 2015 Elsevier B.V. All rights reserved.