Abstract
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.
Highlights
We investigated the superhydrophobic properties of the hierarchical structure of anodic aluminum oxide (AAO) modified with a self-assembled monolayer coating
The results suggest that hierarchical structures can be fabricated by modulating the anodization voltages, and that the PW step influences both Dp and Dint of the second anodization region, but not of the third anodization region
The pillar structure does not show a unified AAO produced under the mild anodization (MA) → PW → hard anodization (HA)
Summary
As superhydrophobic surfaces have high static contact angles (CA) greater than 150◦ with water droplets, they have recently attracted much interest in surface science due to their utility in a range of applications, including self-cleaning, anti-icing, oil–water separation, and anticorrosion processes [1,2,3,4,5,6,7,8,9,10,11,12,13].To create such a surface for these various applications, fabrication techniques for creating micro- and/or nanostructures on surfaces coated with low surface-energy materials must be developed. As superhydrophobic surfaces have high static contact angles (CA) greater than 150◦ with water droplets, they have recently attracted much interest in surface science due to their utility in a range of applications, including self-cleaning, anti-icing, oil–water separation, and anticorrosion processes [1,2,3,4,5,6,7,8,9,10,11,12,13]. It is of great scientific significance and industrial value to be able to fabricate functional superhydrophobic surfaces on aluminum alloys
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