Nonlinear dynamics of chemically active microdrops grants an insight into interfacial chemistry

Active emulsions are complex physicochemical systems that may provide a model for biological phenomena such as RNA polymerase clusters. Theoretical understanding of the physical chemistry of active emulsions is key for reliable modeling of these systems. We consider the simplest "building block" of an active emulsion: a microdroplet undergoing gradual micellar solubilization in the bulk of surfactant solution. In experiments, dissolving droplets may spontaneously induce a flow in the surrounding fluid. Our model links the features of the flow around the drop with the characteristics of nonlinear surfactant sorption kinetics and nonlinear chemical reaction at the droplet interface. We show that continuous assembly of micelles may act as a cleaning mechanism preventing the formation of a continuous monolayer of surfactant monomers even when bulk surfactant concentration exceeds CMC. Our asymptotics reveals that the Marangoni flow velocity depends heavily on the reaction rate and micelle size, while numerical simulations indicate that nonlinear kinetics of micelles production allows for multistability of flow regimes.