Superhydrophobic ceramic coatings with lotus leaf-like hierarchical surface structures deposited via suspension plasma spray process

In this work, superhydrophobic yttria-stabilized zirconia coatings were deposited via the suspension plasma spray process using a new water-based suspension. The new water-based suspension was prepared with the addition of surfactant, which showed a much lower surface tension than the conventional water-based suspension, and meanwhile was much cheaper and safer, and more environmentally friendly than the ethanol-based suspension. The coatings exhibited lotus leaf-like hierarchical surface structures of micron-sized protuberances with superimposed nanometer-sized splats/particles. After chemical modification, the coatings showed excellent water repellency with a water contact angle of ∼157°, a roll-off angle of ∼5°, and complete droplet rebound behaviors. The ethanol-based suspension and conventional water-based suspension were also prepared and used for coating deposition. Comprehensive characterizations of the suspension properties (surface tension, viscosity, atomization behaviors), surface structures, and wetting behaviors of different coatings were conducted for comparative investigation. The formation mechanism of different surface structures was elaborated by investigating the properties of suspensions and plasma gas flow, the aerodynamic breakup behaviors of suspensions, and the motion of impinging particles. The different wetting behaviors of coatings were correlated with the surface structures and wetting states. The study provides a rapid and cost-effective way to deposit hierarchically-structured superhydrophobic ceramic coatings via the water-based suspension plasma spray process.