Superhydrophobic New Zealand leaves: contact angle and drop impact experiments

Dynamic wetting of the adaxial leaf surfaces of several New Zealand native plants has been studied using water drops, contact angle measurements and drop impact experiments. Three native plants (Arthropodium bifurcatum, Euphorbia glauca and Veronica albicans) are identified as superhydrophobic, having advancing contact angles >160 degrees, with <12 degrees hysteresis and <10 degrees roll off angle. These data are comparable to leaves of the lotus (Nelumbo nucifera), an international superhydrophobicity benchmark. Scanning electron microscopy reveals a range of epidermal microstructures and submicron epicuticle wax textures on native leaves, including superhydrophobic microstructures that are similar to those found on exotic leaves. Drop impacts on N. nucifera, A. bifurcatum and E. glauca were filmed using a high speed camera at Weber number between 15 and 200. Drops impacting on the two native plants exhibited asymmetry due to vascular bundles on the leaf surfaces. Biomimicry and dynamic wetting are important for development of industrial superhydrophobic surfaces.