Coalescence-induced propulsion of droplets on a superhydrophilic wire

Droplet transport on a cylindrical wire has applications in numerous fields such as fog collection, mist elimination, filtration, and oil/water separation. This work reports a droplet transport phenomenon on a superhydrophilic wire that shows a transient velocity powered not by the gradient of substrate geometry or wettability but primarily by the surface-to-kinetic energy transition that occurs along the axial direction upon coalescence. The transition efficiency is mainly limited by the viscous friction at the local liquid wedge, a relationship that a modified Ohnesorge number can capture.