Hydrocarbon-induced reversible wetting behaviors of hierarchically-structured yttrium oxide coatings

Abstract

Yttrium oxide is considerably used in protective coatings and functional films in the industry, while the wettability of yttrium oxide surfaces is seldom investigated. In this work, yttrium oxide coatings were deposited via solution precursor plasma spray process using yttrium nitrate solution as feedstock. The phase composition, microstructures, surface topographies, wetting behaviors, and surface compositions of coatings after different post-deposition treatments were characterized comprehensively. The as-sprayed coatings showed dual-scale hierarchical surface structures which were composed of nanometer-sized particles and splats superimposed on micron-sized columnar structures. The as-sprayed coatings were superhydrophilic, whereas they became superhydrophobic after vacuum treatment, exhibiting water contact angles larger than 160°, roll-off angles smaller than 5°, and complete water droplet rebound behaviors. The superhydrophobic coatings also showed high durability in harsh environments which were corroborated by the self-cleaning test, water flushing, and immersion test. The superhydrophobic coatings became superhydrophilic rapidly after high temperature treatment or Ar-plasma treatment, while the coatings regained superhydrophobicity after another vacuum treatment, showing reversible wetting behaviors. The investigations on the surface compositions of coatings with different wettability were conducted, indicating hydrocarbon adsorption on the surface in vacuum treatment and desorption during high temperature treatment or Ar-plasma treatment induced the reversible wetting behaviors.