Superhydrophobic Nanostructured Boehmite Coatings Prepared by AlN Powder Hydrolysis

A simple method that exploits the hydrolysis of AlN powder was used to deposit a nanostructured boehmite coating onto a polished sintered alumina substrate. The coating consists of interconnected polycrystalline nanoporous lamellas and exhibits a large specific surface area. Heat treatment of the as‐deposited coating at 500°C transformed it to γ‐alumina, and then to δ‐alumina at 900°C, with no substantial change in the morphology. However, the nanoporosity of the lamellas disappeared after the heat treatment at 900°C. After a subsequent chemical modification of the coatings with various low‐energy‐surface chemicals, that is, carboxylic acids, heptadecafluoro‐1,1,2,2‐tetrahydrodecyl trimethoxy‐silane (FAS), the initially highly hydrophilic coatings were transformed into a hydrophobic ones. Carboxylic acids proved to be less‐effective low‐energy‐surface chemicals because they produce hydrophobic surfaces with a water droplet contact angle of only 135°. A superhydrophobic surface, exhibiting a water‐droplet contact angle of 155°, was prepared by modifying the boehmite or γ‐alumina coating with FAS.