Fabrication of a ZnO nanocolumnar thin film on a glass slide and its reversible switching from a superhydrophobic to a superhydrophilic state

A simple, cost effective way to deposit ZnO thin films on glass slides has been observed under modified hydrothermal (MHT) conditions. The nanocolumnar growth of ZnO on glass surfaces takes place as a result of the hydrolysis of zinc sulfate by ethanolamine at 100 degrees C without employing any templates or surfactants. The evolved superhydrophobic thin film becomes hydrophilic upon UV light exposure and the film reverts back to its original superhydrophobic character upon storage in the dark. The water contact angle switches back and forth from 154 degrees +/- 1 degrees to 15 degrees. Characterization of the ZnO thin films and the nanocolumnar growth mechanism have been discussed.