Fabrication of Superhydrophobic Surfaces with Hierarchical Structures by an Ultrasonic Etch Method

Based on wet etching and ultrasonic cavitation, an ultrasonic etch method was proposed for fabricating micro- and nanoscale hierarchical structures. By ultrasonic etching with isopyknic mixture of nitric acid/ethanol(4%, volume fraction) and hydrogen peroxide (30%, mass fraction) for 2-10 min at room temperature, several hierarchical structures were fabricated on the surfaces of 60Si2Mn, 60(#), T10, Cr06, 65Mn and silicon steel. After decorated with fluorosilane, the aforementioned surfaces become superhydrophobic and show water contact angles of 156.0 degrees, 154.8 degrees, 156.4 degrees, 153.9 degrees, 156.6 degrees and 155.8 degrees, respectively, and the corresponding roll angles are 6.5 degrees, 19.2 degrees, 6.1 degrees, 7.8 degrees, 6.7 degrees and 7.2 degrees, respectively. Compared to the regular etching, the chemical corrosion of ultrasonic etching was enhanced and modified by coupling with cavitation, and therefore could fabricate hierarchical structures. Due to the differences in microstructure morphologies and wetting states of solid/liquid interfaces, the superhydrophobic surfaces prepared show different wetting behavior. The ultrasonic method proposed is simple, inexpensive and available for other metals, thus having potential values in constructing micro- and nanoscale hierarchical structures and superhydrophobic surfaces.