Cluster formation in active emulsion
Boris Kichatov, Alexey Korshunov, Vladimir Sudakov, L. М. Chikishev
Abstract
An active emulsion consists of self-propelled droplets that are dispersed in another immiscible liquid. Under certain conditions, droplet clusters may form in such a system. This study analyzes the process of cluster formation in an octane-in-water emulsion activated by ammonia. The movement of droplets in the emulsion is due to the emergence of the Marangoni flow on the surface of the droplets. It has been found that clusters are formed when the average droplet velocity is less than a certain critical value. The existence of a critical velocity is due to the fact that the rate of droplet attachment to a cluster is proportional to their velocity and the rate of droplet detachment from a cluster is proportional to the square of the droplet velocity. At supercritical droplet velocities, the rate of droplet detachment from a cluster exceeds the rate of their attachment. The critical velocity depends on the droplet density in the emulsion and increases as the droplet density decreases.