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 mu m 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 degrees and similar to 1 degrees for 10 mu L water droplets, and 171 +/- 1 degrees and 6 +/- 2 degrees for 1 mu L 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 degrees) and ethanol-water mixtures (advancing CA above 150 degrees when the surface tension was greater than 35 mN m(-1)).