Switchable wettability of vertical Si nanowire array surface by simple contact-printing of siloxane oligomers and chemical washing

Abstract

The wettability of a vertical Si nanowire (SiNW) array surface, prepared by a metal-assisted chemical etching technique, has been systematically investigated. The simple contact printing of siloxane oligomers has converted a SiNW array surface from superhydrophilic to superhydrophobic. In addition to the contact-printing time of siloxane oligomers, the nanowire length and its aggregation or bundling state have been found to have a profound effect on the wettability. The superhydrophobic state of the SiNWs with printed siloxane oligomers has shown long-term stability, even after prolonged dipping in water. Furthermore, the wettability could be switched reversibly many times, i.e., from superhydrophilic to superhydrophobic or vice versa, by the simple contact printing of siloxane oligomers and chemical washing with sulfuric acid repeatedly. The demonstrated reversible switching of the SiNWs’ surface wettability may be very helpful in many applications.