Surface topography effects on the wettability and antifouling performance of nano-ZnO epoxy composite coatings

Nature-inspired eco-friendly superhydrophobic surfaces have attracted great interests from fundamental research to antifouling application. Nanocomposite coatings are an economical way to fabricate superhydrophobic surfaces. This paper studies how the coating topography can be controlled by using different nanoparticle sizes and concentrations. Six three-dimensional surface parameters are used to define the resulting topography and explore the correlations with wettability. Three unique scenarios are proposed based on the relationship between the two key parameters core void volume (Vvc) and core material volume (Vmc) to assess the relationship between surface roughness and solid-liquid contact area fraction (f). A water contact angle (WCA) of 152.6° and contact angle hysteresis (CAH) of 2.9° are obtained by employing dual-sized nanoparticles at 45% nanoparticle concentration (wt./wt.), which is up to 10% less than the superhydrophobic coating fabricated by using single-sized nanoparticles (30 nm). Furthermore, Vvc and peak sharpness dominate f, consequently dominating the wettability in the transitional state and Cassie state, respectively. The antifouling tests using Phaeodactylum tricornutum and Bacillus sp. show a negative correlation between f and antifouling performance, and the minimum adhesion ratios are only 0.41% and 0.53%, respectively. The superhydrophobic surfaces with Vvc/Vmc > 1 are shown to be better for antifouling applications. These findings are important for designing superhydrophobic nanocomposite coatings for antifouling performance.