Highly hydrophobic Ni-W electrodeposited film with hierarchical structure

Highly hydrophobic Ni-W alloy coating was obtained from chloride-containing bath as an alternative to the classical sulfate-containing bath, on copper substrates. Surface morphology, surface roughness, chemical and phase compositions of the coatings deposited by different current densities in both baths were investigated. Hydrophobicity of the coatings and its effectiveness from the coating characteristics were investigated. The Ni-W coatings obtained from the chloride-containing bath revealed a rough and hierarchical structure different from the smooth ones resulted from the sulfate-containing bath. Both types of the coatings were hydrophilic immediately after electrodeposition, but, they changed to hydrophobic after two weeks storing in the air. The rough Ni-W coatings provided a more hydrophobic property (water contact angle ~131°) as compared to that of smooth coatings (water contact angle ~96°). The reason was attributed to the hierarchical structure of the coating surface in addition to its effectiveness during air storage.