Understanding the correlations between the mechanical robustness, coating structures and surface composition for highly-/super-hydrophobic ceramic coatings

Highly-hydrophobic dense Yb2O3 coatings with bump structures and relatively flat topographies were deposited via the solution precursor vacuum plasma spray (SPVPS) process, and superhydrophobic porous coatings with distinct columnar structures were deposited via the solution precursor atmospheric plasma spray (SPAPS) process. The SPVPS coating exhibited a water contact angle (WCA) of similar to 155 degrees and a roll-off angle (RA) of similar to 28 degrees, while the SPAPS coating exhibited a WCA of similar to 163 degrees and RA of similar to 3 degrees. The SPVPS coatings maintained high microstructure integrity and relatively consistent hydrophobicity after a comprehensive set of mechanical tests, showing a much higher mechanical robustness. In contrast, the columnar structures of the SPAPS coatings were severely damaged by mechanical contacts, resulting in a sharp WCA decrease. The WCA of the abraded coatings increased after vacuum treatment due to hydrocarbon re-adsorption; the abraded SPAPS coating regained its initial superhydrophobicity while the SPVPS coating showed a mild WCA increase. The surface structures and compositions of the original coatings, the abraded coatings and vacuum-treated coatings were investigated, revealing close correlation of the changes in WCA with the surface composition and structures.