Communication: anti-icing characteristics of superhydrophobic surfaces investigated by quartz crystal microresonators

We investigated the anti-icing characteristics of superhydrophobic surfaces with various morphologies by using quartz crystal microresonators. Anodic aluminum oxide (AAO) or ZnO nanorods were synthesized directly on gold-coated quartz crystal substrates and their surfaces were rendered hydrophobic via chemical modifications with octyltrichlorosilane (OTS), octadecyltrichlorosilane (ODS), or octadecanethiol (ODT). Four different hydrophobic nanostructures were prepared on the quartz crystals: ODT-modified hydrophobic plain gold (C18-Au), an OTS-modified AAO nanostructure (C8-AAO), an ODS-modified AAO nanostructure (C18-AAO), and ODT-modified ZnO nanorods (C18-ZnO). The water contact angles on the C18-Au, C8-AAO, C18-AAO, and C18-ZnO surfaces were measured to be 91.4°, 147.2°, 156.3°, and 157.8°, respectively. A sessile water droplet was placed on each quartz crystal and its freezing temperature was determined by monitoring the drastic changes in the resonance frequency and Q-factor upon freezing. The freezing temperature of a water droplet was found to decrease with decreases in the water contact radius due to the decreases in the number of active sites available for ice nucleation.