Jet impingement on wettability-patterned surfaces*

The orthogonal impingement of liquid jets on flat, impermeable substrates is useful for a number of applications. Impingement on a wettable surface possessing a sufficient downstream liquid depth leads to the formation of a classical hydraulic jump, where the jet forms a thin film on the substrate up to a distance from the point of impact and then the liquid film height suddenly increases. On the other hand, a downstream depth cannot be sustained on a superhydrophobic surface. Therefore, upon impact on such surfaces, the liquid jet spreads radially as a thin film, which subsequently breaks up into droplets that are randomly ejected. A wettability-patterning technique is demonstrated in the present work that can delay or even eliminate droplet breakup for jet impingement on horizontal superhydrophobic substrates. An analysis for the prediction of the hydraulic jump and droplet breakup locations is presented, thus facilitating the design of the wettability pattern required to cause a desired outcome. The model is further extended to determine the radial variation of the competing forces.