Study of wettability transition on hierarchical structured aluminum cut by wire electric discharge machining

Abstract Many studies have investigated the wettability transition of metal surfaces with a variety of micro- or nanostructures. Previous research focused on the influence of different materials, atmospheric conditions, and roughness, but not on the relationship between surface structure and transition. In this paper, the transition process has been shortened by fabricating microgroove arrays on aluminum. All the samples’ contact angle increased, and exceeded 150° in a few days. Some samples reached superhydrophobicity in 1 day. Grooves with a large width and steeper side wall turned superhydrophobic earlier than those with narrower grooves and a higher side wall angle. X-ray photoelectron spectroscopy analysis(XPS) of each day indicated that absorption of organic materials contributed to the lowering of the metal’s surface energy. Analysis of the energy transition showed that grooves with steeper side wall and larger widths had a similar advantage in terms of water repellency. These structures become superhydrophobic more quickly as the surface energy decreases.