Dissolution of a Drop on a Liquid Surface Leading to Surface Waves and Interfacial Turbulence

Abstract

If a droplet of liquid with a lower surface tension than that of water and partially soluble in water is deposited on a free water surface, it spreads, dissolves, and simultaneously creates surface tension gradients leading to Marangoni instability and interfacial turbulence. In a first stage, if the solubility of the drop is not too high, there is formation of patterns that evolve in time, eventually leading to interfacial turbulence and droplet disappearance. These patterns, which on occasion last quite long time intervals, result from the interaction and collision of surface waves sustained by the surface tension gradient. These surface waves have been observed with a Schlieren device and their characteristics (e.g., shape, velocity) have been measured. Two types of surface wave profiles exist: wave profile like a “hump” (sech-like) or like a hydraulic jump (tanh-like). We have followed their time evolution and for head-on, oblique, and overtaking collisions we have measured their trajectories. We have been able to correlate our experimental findings with available theoretical, albeit qualitative, results known about waves and shocks.