Highly hydrophobic nickel and nickel-tungsten coatings: Microstructural and surface properties

Ni and NiW coatings with micro-nanoscale hierarchical structures were obtained by a two-step electrodeposition process. A detailed statistical analysis was performed on SEM images to clarify the effect of tungsten, as an alloying element, on the surface morphology of Ni. In the presence of tungsten, the circularity parameter of Ni coating highly increased from 0.49 to 0.77, and a more regular and orderly distribution of micro colonies was obtained. The surface roughness parameters of the coatings were obtained using AFM profile analysis. The static contact angles of Ni and NiW coatings were measured by a set of four different polar/non-polar liquids. The Wu model was then used to translate the contact angle data to surface free energies. According to the obtained results, the storage time of Ni and NiW coatings in the air greatly affects the polar component of their surface free energies. This could be due to the adsorption of airborne hydrocarbons followed by a gradual increase of hydrophobic carboxylic groups on the coating surface.