Fabrication of a superhydrophobic etched copper-silver/stearic acid composite coating and evaluation of its friction-reducing and anticorrosion abilities

A copper substrate was etched in the mixed solution of (NH4)(2)S2O8 and HCl by oxidation-assisted surface acid etching process to generate a desired roughened structure (coded as etched Cu). Resultant etched Cu surface was then immersed in silver nitrate solution to allow incorporation of silver submicro-particles through replacement reaction to afford a lotus-leaf-like structure (denoted as etched Cu-Ag). Etched Cu-Ag surface was finally modified with stearic acid (abridged as STA) to provide etched Cu-Ag composite coating with superhydrophobicity (coded as etched Cu-Ag/;STA). The morphology and microstructure of as-prepared etched Cu-Ag surface were observed with a field-emission scanning electron microscope, and its friction-reducing and anticorrosion abilities were evaluated in relation to water contact angle measurements. It was found that the as-prepared etched Cu-Ag surface is composed of micro-protrusions and submicro-mastoids with dual-scale structure similar to that of the lotus leaf. Besides, etched Cu-Ag/;STA composite coating has a static water contact angle of 160.5 and shows very low adhesion for water droplet, and it possesses good friction-reducing ability. The evaluation of its anticorrosion ability indicates that the superhydrophobic surface has a certain anticorrosion ability against the solution whose pH values are within 59. Moreover, the water contact angles (WCAs) of the superhydrophobic surface almost remain the same after immersion in the solution with different pH values, but its contact angle hysteresis values (CAHs) increase slightly thereafter. The method and results show potential application for protection of Cu substrate in engineering.