Surface explosions when oil, water, and alcohol mix!

When an immiscible oil is deposited over soapy water, a liquid lens is formed. Subsequently, when a smaller droplet of ethanol-water mixture is deposited on the oil lens, rupture occurs within a few minutes. This rupture time is found to depend on the shape and size of the liquid lens and the concentration of the ethanol-water mixture. The rupture can be attributed to the moment when the ethanol-water mixture comes in contact with the miscible soapy water solution. Spontaneous emulsification and the density-difference (Rayleigh-Taylor instability) phenomenon influence the ethanol-water descent. Rupture is characterized by a large radial but thin circular film rapidly expanding (<2 ms) to a radius often larger than the original oil lens. The phenomenon continues as the radius then retracts towards the center and the now non-uniform ethanol-water mixture forms a fingering instability (< 4 ms), finally retracting to near-zero radii. Data from high-speed imaging predicts a power law correlation for this thin film spreading behavior.