New perspectives on structural parameters and hydrophobic model inspired by a superhydrophobic Cu cone-flower coating

Abstract

Superhydrophobic films have been successfully prepared on various substrates by finely controlling surface micro/nanostructure's roughness and reducing surface energy. However, there is no unified conclusion about the correlation of surface roughness and 3D volume parameters to wettability. Herein, we fabricated a superhydrophobic film composed of hierarchical Cu cone-flowers via facile one-step pulse electrodeposition with a 30% duty cycle for 20 min. Based on this film, the relationship between roughness/volume parameters and hydrophobicity was well studied. The resulting cone-flower film exhibits excellent corrosion resistance and self-cleaning properties due to a high water contact angle (WCA) of ~160° and a low sliding angle (SA) of ~3°. The large roughness skewness (Rsk = 0.7–1.3) and void volume ratio (Vvc/Vmc > 1.5) are shown to be more desirable to achieve superhydrophobic surfaces. Moreover, a new hydrophobic model is proposed to explain the above results, which means that the nanoscale air cushions share most of the gravity of water droplets to help microscale air cushions closer to the Cassie state. Further experiments by adding or destroying the nanostructures to observe the change of hydrophobicity well verified our conjecture.