Ultra-quick dynamics and acrobatics of viscous marbles.

Abstract

Non-wetting viscous drops are unusually quick compared to wetting ones, owing to the conjunction of non-wetting (which minimizes the contact with the substrate) and rotation (which minimizes the dissipation inside the liquid). Here, we report the existence of a threshold in driving force above which the speed of these objects increases about tenfold compared to previous models and experiments. We find that this effect is due to a dynamic reduction of the contact, that minimizes even more the interaction with the substrate but can also render the dynamics non-stationary - a consequence of the geometrical transformations of fast revolving drops. Paradoxically, viscosity enables this regime by impeding rapid contact equilibration, thereby reducing substrate interactions in fast-moving drops.