Tuning Superhydrophobic Materials with Negative Surface Energy Domains

Hydrophobic/superhydrophobic materials with intrinsic water repellence are highly desirable in engineering fields including anti-icing in aerocrafts, antidrag and anticorrosion in ships, and antifog and self-cleaning in optical lenses, screen, mirrors, and windows. However, superhydrophobic material should have small surface energy (SE) and a micro/nanosurface structure which can reduce solid-liquid contact significantly. The low SE is generally found in organic materials with inferior mechanical properties that is undesirable in engineering. Intriguingly, previous theoretical calculations have predicted a negative SE for θ-alumina (θ-Al₂O₃), which inspires us to use it as a superhydrophobic material. Here, we report the experimental evidence of the small/negative SE of θ-Al₂O₃ and a θ-Al₂O₃-based superhydrophobic coating prepared by one-step scalable plasma arcing oxidation. The superhydrophobic coating has complete ceramic and desired micro/nanostructure and therefore exhibits excellent aging resistance, wear resistance, corrosion resistance, high-temperature tolerance, and burning resistance. Owing to the rarity of the small/negative SE in inorganic materials, the concept to reduce SE by θ-Al₂O₃ may foster a blowout to develop robust superhydrophobicity by complete inorganic materials.