Ultrasonic-assisted fabrication of superhydrophobic ZnO nanowall films

Abstract

Zinc oxide-based superhydrophobic surfaces were fabricated on aluminium oxide-seeded glass substrates via sonochemical approach by varying the parameter, the sonication time duration. The fabricated structures have nanowall-like morphology with an average long axis length and thickness of ${\sim }300$ and ${\sim }40~\hbox {nm}$, respectively.  The surface roughness created by surface-modified ZnO nanowalls and the air pockets trapped within the dense nanowalls, transformed the hydrophobic glass substrates into superhydrophobic surfaces with water contact angle of $156{^{\circ }}$ during 20 min of sonication. An independent analysis was carried out to study the growth of ZnO nanowalls over glass substrates in the absence of the aluminium oxide seed layer and sonication process. The results suggested that the synergistic effect of the aluminium oxide seed layer and sonochemical process can enable the formation of ZnO nanowall structures favourable for superhydrophobic property. A possible growth mechanism of ZnO nanowalls formation during sonication process has been discussed in detail.