Triple-Scale Structured, Superhydrophobic and Highly Oleophobic Surfaces

We prepared triple-scale structured, superhydrophobic films via a layer-by-layer particle deposition approach: large silica particles (1.2 μm in diameter) were first partially embedded in an epoxy matrix, followed by electrostatic deposition of medium (180 nm) and small (20 nm) particles. Mechanical robustness of the triple-scale structured coating was enhanced by SiCl₄-based cross-linking between silica particles. After chemical modification with a perfluoroalkyl silane, the triple-scale structured surface was turned superhydrophobic, on which the contact angle (CA) and roll-off angle were 167 ± 3° and ∼1° for 10 μL water droplets, and 171 ± 1° and 6 ± 2° for 1 μL water droplets, respectively. The triple-scale surface roughness was especially effective in achieving low roll-off angles for small droplets. The triple-scale structure demonstrated much higher stability for the non-wetting Cassie state for water over a dual-scale structure, as experimentally verified by a compression test. In addition, the triple-scale structured surface was also highly oleophobic, as evidenced by high CAs for hexadecane (134 ± 3°) and ethanol-water mixtures (advancing CA above 150° when the surface tension was greater than 35 mN m ^-1).