Hybrid numerical method for interfacial flow with soluble surfactant and its application to an experiment in microfluidic tip streaming

This chapter describes a hybrid numerical method for solving problems of two-phase flow with soluble surfactant in the limit of large bulk Peclet number. Most numerical studies of the effect of surfactant on the deformation and breakup of a single bubble or drop in an imposed flow are for insoluble surfactant, that is, for surfactant that is confined to the interface alone. A soluble surfactant advects and diffuses in the bulk fluid as a passive scalar, but when local interfacial surface area is changed during deformation, the surface and bulk surfactant concentrations are brought out of equilibrium. This causes an exchange or transfer of surfactant between its dissolved form in the bulk and its adsorbed form on the interface that acts so as to restore equilibrium between the two surfactant phases.