Spontaneous dewetting on a volatile drop floating on a liquid bath

International audienceWe explore the evolution of a drop of ethanol floating on a bath of silicone oil. Initially, the system exhibits pseudo-total wetting, in which a film of oil covers the drop. The ethanol evaporates through the film generating thermal Marangoni flows in the drop. At this stage, the film of oil undergoes a gravitational instability reminiscent of the Rayleigh-Taylor instability. At a later stage, we observe the film of oil to spontaneously dewet the drop. This is explained by the change in sign of the oil-on-ethanol spreading parameter due to the penetration of some oil into the ethanol drop, the timescale of which is presumably accelerated by the Marangoni flows. At a later stage, a branch-like structure is observed on the drop surface and it appears to be the footprint of ongoing Marangoni flows. We experimentally characterize the system temperature field, evaporative flux, flow speed and spreading parameters, and we rationalize the various stages of the evolution of the drop