Multitude of singular jets during the collapse of drop-impact craters

Abstract

We study singular jets from the collapse of drop-impact craters, when the drop and pool are of different immiscible liquids. These jets emerge from a dimple at the bottom of the rebounding crater, when no bubble is pinched off. The parameter space is considerably more complex than for identical liquids, revealing intricate compound-dimple shapes. In contrast to the universal capillary-inertial drop-regime, where the pinch-off neck radius scales as $R\sim t^{2/3}$, a purely inertial air-dimple has $R \sim t^{1/2}$ and is sensitive to initial and boundary conditions. Capillary waves can therefore mold the dimple into different collapse shapes, with normalized jetting speeds one order of magnitude larger than for jets from bursting bubbles. We study the cross-over between the two power-laws. The fastest jets can pinch off a toroidal micro-bubble from the cusp at the base of the jet.