Superhydrophobic brass and bronze meshes based on electrochemical and chemical self-assembly of stearate

The preparation and characterization of superhydrophobic membranes formed on metal meshes (brass and bronze) by coating from stearic acid is presented. The membranes were prepared by two methods: electrolysis and acid etching. The electrolysis process is a one-step method performed by anodizing the mesh in ethanol solutions of stearic acid. Stearic acid concentration, support electrolyte concentration and electrolysis time were systematically varied. Nanostructures, including nanotubes, are induced on the metallic filaments. Analysis by FTIR, XRD, XPS and SEM of surfaces and precipitated material indicate that formed nanostructures are assemblies of metallic stearates on the surface (copper and/or zinc stearates). Superhydrophobicity (contact angles larger than 150 degrees) was only achieved (in the electrolysis method) in cases where the formation of nanotubes was observed. On the other hand, the acid etching process is a two-step method: immersion of the meshes in acid solution of CuCl2 or FeCl3, oxidizing the surface with formation of inorganic salts nano crystals, followed by immersion in stearic acid solution. Organic nanostructures (nanoribbons and/or nanopetals) were observed after the second step. Superhydrophobic surfaces (contact angles between 150 and 170 degrees) were obtained for all the membranes. Both kind of membranes (electrolysis and etching) resulted effective in oil-water separation.