Jet ejection following drop impact on micropillared hydrophilic substrates

Abstract

The jetting phenomenon from impinging droplets on partially wetting hydrophilic substrates composed of cylindrical micropillars is studied. Impact velocity and fluid viscosity are varied to characterize the jets. It is found that the jetting phenomenon arises for certain ranges of Weber and Ohnesorge numbers. Jet speed, height, and diameter scale linearly with the Weber number. The scaling analysis indicates that the jet is produced by pure inertial focusing of radial flow due to the collapse of an air cavity formed at the center of the drop during the recoiling phase of the impact.