A comparative study of droplet impact dynamics on a dual-scaled superhydrophobic surface and lotus leaf

The impact dynamics of water droplets on an artificial dual-scaled superhydrophobic surface was studied and compared with that of a lotus leaf with impact velocity V up to 3 m/s. The lower critical impact velocity for the bouncing of droplets was about 0.08 m/s on both surfaces. At relatively low impact velocities, regular rebound of droplets and air bubble trapping and flow jetting on both surfaces were observed as V was increased. For intermediate V, partial pinning and rebound of droplets were found on the artificial dual-scaled surface due to the penetration of the droplets into the micro- and nano-scale roughness. On the lotus leaf, however, the droplets bounced off with intensive vibrations instead of being partially pinned on the surface because of the irregular distribution of microbumps on the leaf. As the impact velocity was sufficiently high, droplet splashing occurred on both surfaces. The contact time and restitution coefficient of the impinging droplets were also measured and discussed.