Inverse infusion processed hierarchical structure towards superhydrophobic coatings with ultrahigh mechanical robustness

Poor mechanical durability still hinders artificial superhydrophobic coatings from practical application, although these coatings were created years ago and still attract wide research interest. Previous epoxy/nanoparticle works seem to encounter a dilemma: a delicate nanostructure and low surface energy without a proper and strong microstructure to provide protection and strength naturally leads to weak mechanical adhesion and poor wear robustness. Herein, we develop an inverse infusion process (IIP) to construct hierarchical structures via newly synthesized hydrophobic and tough epoxy resin as well as rationally selected alumina nanoparticles (NPs). The IIP process forms an uncured epoxy layer first on the substrate and a preliminary nanocomposite coating next using an air spraying method, after which the epoxy layer inversely infuses into the micro/nanostructure and constructs a tougher microstructure on the top as well as a continuous nanocomposite layer throughout the coating after curing. This results in superhydrophobic coatings on a substrate with excellent adhesion and mechanical robustness, and our coatings can tolerate 600 cycles of tape peeling tests (with 3 M high-tack tape), 20 m sandpaper abrasion (with a pressure of ~5 kPa and 80 grit sandpaper), 115 cycles of Taber abrasion (with 250 g load), and 600 g of sand impact from a height of 110 cm, which are the highest values achieved by superhydrophobic coatings to the best of our knowledge. Furthermore, our coatings sustained highly corrosive media, such as sodium hydroxide and hydrochloric acid solutions. A combination of the established IIP process and the rationally selected ingredients dramatically enhanced the mechanical durability of the superhydrophobic coatings, and these attractive materials may attract attention for self-cleaning, anti-icing, and anti-fouling applications in industry.