Organophilic nano-alumina for superhydrophobic epoxy coatings

Bilayer coatings with high hydrophobic characteristics were successfully prepared by depositing alumina nanoparticles functionalized with stearic acid as top layer paint onto epoxy -based bottom coatings. More stable alumina suspensions were obtained with reflux in 2-propanol than in toluene. The dispersions of functionalized alumina NP (2 wt% and 3 wt%) in 2-propanol were applied by the spray-coating method on a stainless steel substrate previously coated with two different partially cured epoxy -based coatings: DGEBA and Novolac Type II. Results show that DGEBA-based coatings with functionalized alumina NPs displayed superhydrophobic characteristics with very little interaction with water droplets, typical of the Cassie state, due to the low surface energy promoted by the functionalized alumina NPs. The alumina-modified Novolac Type II coating presented WCA in the range of 140-145 degrees, with strong adhesion of water droplets to the surface, characteristic of the Wenzel state, which is related to the other fillers present in the commercial resin. Based on these results, it was possible to develop superhydrophobic coating by using a fast, cost effective and environmentally-friendly approach which can be scalable to relatively great surfaces, involving alumina functionalized with fatty acids and epoxy resins with controlled curing process.