Coalescence of armored interface under impact

Armored interfaces refer to fluid interfaces on which a compact monolayer of particles is adsorbed. In this paper, we probe their robustness under impact. For such an investigation, the impact of a drop (covered or not by particles) on a flat armored interface is considered. Two regimes are observed: small drops impacting at low velocities do not coalesce, while bigger drops falling at higher velocities lead to coalescence. The coalescence which occurs when the impacting drop has just reached its maximum extension directly results from the formation of bare regions within the armor. We therefore propose a geometric criterion to describe this transition. This simple modeling is able to capture the dependence of the measured velocity threshold with particle size and drop diameter. The additional robustness experienced by double armors (both drop and puddle covered) results in an increase of the measured velocity threshold, which is quantitatively predicted.