When two liquid droplets coalesce on a super-repellent surface, the excess surface energy is partly converted to upward kinetic energy, and the coalesced droplet jumps away from the surface. However, the efficiency of this energy conversion is very low. To overcome this, we used a simple and passive technique consisting of superomniphobic surfaces with a protruding macrotexture, comparable to the droplet size, to demonstrate coalescence-induced jumping with an energy conversion efficiency of 18.8%, i.e., about 570% increase compared to superomniphobic surfaces without a macrotexture. The higher energy conversion efficiency arises primarily from the effective redirection of in-plane velocity vectors to out-of-plane velocity vectors by the macrotexture. This higher energy conversion efficiency allows coalescence-induced jumping of droplets with low surface tension and very high viscosity, even at Ohnesorge number greater than 1.

This video illustrates the coalescence-induced self-propulsion of two droplets of water on a superomniphobic surface without a ridge and with a ridge. The higher energy conversion efficiency with a ridge is evident from the higher jumping height.

See publication:
H. Vahabi, W. Wang, J. M. Mabry and A. K. Kota, Science Advances, 2018, DOI: 10.1126/sciadv.aau3488

свернуть