Controlled jetting of impacting drops.

Abstract

Controlling the behavior of impacting droplets continues to remain a challenge. We demonstrate a simple method of inclining a plane superhydrophobic surface with a sudden wettability change in the form of a superhydrophilic spot to control the droplet impact dynamics. We find that, depending on the operating conditions, the impacting drops can exhibit two distinct regimes: no-splitting and jetting. We characterize the transition between the regimes in terms of the ratio of the Weber number to the Bond number, the spot diameter, and the surface inclination angle using experiments and predict the transition using a scaled theoretical model. We study the jet angle and diameter of the ejected droplets using experiments and scaled theoretical models in terms of an energy ratio comprising relevant energies of the system. In addition to the advances in the physics of drop impact, uniquely, our study may find relevance in practical applications that require delivery of an ejected droplet of a particular size at a desired orientation onto a target substrate.