Multilevel hierarchy of fluorinated wax on CuO nanowires for superoleophobic surfaces

We demonstrate the multilevel hierarchy of nanoscale wax crystals on nanowire (NW) structures that strongly repels not only water but also olive oil and hexadecane. We deposited C24F50-fluorinated wax (F-wax) using thermal evaporation on the surface of CuO NWs. Fluorinated wax crystals are self-assembled on the CuO NWs forming three-dimensional hierarchical structures. The achieved multilevel hierarchy has strongly repelled water, glycerol, ethylene glycol, and olive oil with contact angles (CAs) exceeding 160°. When sufficient F-wax is crystallized on the CuO NWs, crystals that are assembled perpendicularly to the longitudinal NW axis form a re-entrant curvature allowing superoleophobic characteristics with strong repellence of hexadecane with CAs of ∼150° and a small contact angle hysteresis of <10°. Furthermore, the surfaces can repel extremely small water droplets (∼100 pL), an indication of an ability to withstand condensation. These types of multilevel hierarchies can be formed on numerous roughened surfaces as the wax can be easily applied to various substrates without affecting the mechanical integrity of base structures.