Superhydrophobic behavior of polymer-coated nanowire-arrays as a function of interfacial affinity and etching

We have investigated the superhydrophobic behavior of coatings of polydimethylsiloxane (PDMS) and polystyrene (PS) on ZnO nanowire-arrays. PDMS produced a conformal coating on the ZnO nanowires due to high interfacial affinity between ZnO and PDMS, resulting in a large water contact angle of 168.0° (compared to 108.8° for planar PDMS surfaces) and droplet roll-off angles that were too small to measure. The superhydrophobicity of these coatings is among the largest reported for any polymeric coating. PS instead preferentially coated the bases of the ZnO nanowires and valleys between nanowires due to low interfacial affinity between ZnO and PS, resulting in a water contact angle of 149.3° (compared to 90.5° for planar PS surface) and droplet roll-off angles of 5°-8°. If, however, the ZnO nanowires were etched away after PS deposition, hollow tube-like nanostructures of PS were left behind, and exhibited a water contact angle of 164.3° and droplet roll-off angles of 1°-2°. These nanostructured PS coatings offer unique potential for food-safe superhydrophobic coatings because they consist only of PS without any inorganic components.