Systematic Control of Anodic Aluminum Oxide Nanostructures for Enhancing the Superhydrophobicity of 5052 Aluminum Alloy

The recent increased interest in the various applications of superhydrophobic surfaces necessitates investigating ways of how this property can be enhanced further. Thus, this study investigated how superhydrophobic properties can be enhanced through the formation of anodic alumina nanostructures on 5052 aluminum alloy. A multistep anodizing process that alternates two different anodizing modes, mild anodization (MA) and hard anodization (HA), with an intermediate pore-widening (PW) process was employed. Multistep anodization was employed in two different ways: an MA → PW → HA process and an HA → PW → MA process. Both routes were conducted with PW durations of 40, 50, and 60 min. The well-defined nanostructures were coated with a self-assembled monolayer (SAM) of FDTS (1H, 1H, 2H, 2H-perfluorodecyltrichlorosilane). The contact angle values of water droplets were maximized in the pillar-like nanostructures, as they have a less solid fraction than porous nanostructures. With this, the study demonstrated the formation mechanism of both nanoscale pillar and nanoscale hierarchical structures, the wettability of the superhydrophobic surfaces, and the relationship between PW duration time with wettability and the solid fraction of the superhydrophobic surfaces.