A layered superhydrophobic coating with excellent mechanical robustness and anti-corrosion performances

Lotus-like superhydrophobic coatings play an essential role for the corrosion protection of steel substrates exposed to harsh environments. Thus, improving the mechanical robustness and corrosion resistance of superhydrophobic coatings through macroscopic material matching and microscopic structure manipulation is an important task. In this study, a layered superhydrophobic coating with a "1 + 1" structural mode was successfully prepared using the spinning and spraying techniques. In order to prevent the interface debonding of upper and lower layers, the epoxy resin was introduced as bonding transition zones, and its three-dimensional cross-linking characteristic was used to realize the super stable "welding". Then, the structure-function design, surface wetting behavior, mechanical robustness and corrosion resistance were systematically investigated. The results showed that the superhydrophobic coating was successfully constructed by designing micro-/nano-scale hierarchical structure and reducing surface energy, achieving a desirable static contact angle of 172.5° and a roll-off angle of 3.4°. Through high-pressure water anti-jetting, high-height sand impacting, and loaded sandpaper shear abrasion tests, the as-prepared coating still showed obvious superhydrophobicity and the shapes of water droplets on the coating surface continued to be nearly spherical. After immersion in 5 wt% NaCl solution for 28 days, an increase of polarization current density was negligible (∼0.0035 μA/cm2), and the impedance values (107 Ω•cm2) of the superhydrophobic coating were approximately three orders of magnitude higher than the control coating in the low-frequency region. This was because the corrosive species (H2O and Cl−) were restricted from entering the coating interior owing to the extreme water-repellence. In addition, the electron-carrying capacity of the superhydrophobic coating was vastly weakened, which impeded the formation of the corrosive conductive circuit and improved the anti-corrosion properties, prolonging the service life of the polymer coating system.