Hydrophobic/hydrophilic switching on zinc oxide micro-textured surface

Switchable wettability of zinc oxide (ZnO) microrod coated surfaces was controlled in two different ways: (1) by physical geometry (surface coverage area S-A: the area covered by solid) and (2) by irradiation with ultraviolet (UV) light followed by infrared (IR) or furnace heating. In the first approach, the threshold coverage area for achieving hydrophobic surfaces was found to be <40%, which is in good agreement with predicted values in the literature leading to a metastable Cassie-Baxter regime. The transformation of hydrophobic to hydrophilic surfaces was studied by alternating cycles of 3 h exposure to ultraviolet (lambda(peak) similar to 253 nm) light followed by 1 h of annealing or IR irradiation alone. Three different annealing temperatures (120 degrees C, 200 degrees C and 250 degrees C) were utilized. Results of this work can be applied for designing surfaces with controlled wettability. (C) 2012 Elsevier B. V. All rights reserved.