Remobilizing Surfactant Retarded Fluid Particle Interfaces. II. Controlling the Surface Mobility at Interfaces of Solutions Containing Surface Active Components

Abstract

Convection of adsorbed surfactant along a fluid particle surface can accumulate surfactant at the trailing end of the particle. The nonuniform surface tensions that result cause Marangoni stresses which retard the surface mobility. This is the second part of a two-part study on controlling the mobility of surfactant laden interfaces. In Part 1 (Phys. Fluids A 3, 3 (1991)), we established that a surfactant that is kinetically quickly exchanging at concentrations above its CMC can be used to control the surface mobility. Micelles of the surfactant, acting as monomer sources, keep the sublayer concentration uniform at the CMC. The surface concentration, in equilibrium with the sublayer, is made uniform and the Marangoni stresses along the interface are removed. A range of stress conditions from significantly retarded to stress-free interfacial motion can be achieved by varying the surfactant concentration about the CMC. In this study, it is demonstrated that this regulation mechanism is effective even when one of the fluid phases contains surface active components that by themselves would retard the surface flow. For this case, the concentration of remobilizing surfactant can be made large compared to the concentration of the other surface active components. The remobilizer therefore dominates adsorption along the interface and prevents the significant adsorption of the retarding surface active components. Surface mobility control is demonstrated experimentally using a three-phase periodic fluid particle flow that is very sensitive to Marangoni stresses. © 1994 Academic Press. All rights reserved.