Explosive spreading of a concentrated emulsion over a liquid surface

Abstract

Spreading of a droplet of a concentrated oil-in-water emulsion over a water surface has been monitored. At the initial moment, this process proceeds at a high rate like an explosion. The stationary spreading is soon followed by the development of instability with the formation of a flower-shaped structure. At the final stage, the spot of the spread liquid may somewhat shrink. The characteristic times of these three stages are about 0.1, 1, and 10 s. The explosive character of the initial stage of spreading may be explained by the loss of dimensionality (3D → 2D) and the passage of the dispersion medium into the aqueous substrate with the release of a high free energy, while the subsequent spreading of the oil spot is explained by the Marangoni effect. A decrease in the energy of the interaction between dispersed phase (“oil”) particles in the emulsion leads to the phase separation. The final shrinkage of the oil spot may be due to the surface wave disturbance, which arises upon the explosive phase separation in the emulsion.