Flow-Induced Coalescence in Protein-Stabilized Highly Concentrated Emulsions:  Role of Shear-Resisting Connections between the Droplets

Abstract

This work focuses on flow-induced coalescence in highly concentrated emulsions stabilized by bovine ß-lactoglobulin. In these systems, flow-induced coalescence results in separation of oil. The amount of oil separated increases with the intensity of the flow treatment and reaches a plateau value above a certain intensity of the flow treatment. In this work, the flow treatment was chosen to be sufficiently intense to reach this plateau value. The oil separation increased roughly linearly with the volume fraction of emulsion droplets, starting at a critical volume fraction of approximately 0.90. Furthermore, at constant volume fraction, the oil separation increased with the time lapse during which the emulsion had been at this volume fraction. It reached a maximum value, which did not depend on the electrolyte concentration but was higher for calcium ions than for sodium ions. The rate at which the oil separation reached this maximum value increased with the electrolyte concentration. These observations are explained on the basis of a previously developed mechanism of flow-induced coalescence, in which the sensitivity to flow-induced coalescence is related to a slip¿stick transition between the surfaces of the thin films between emulsion droplets, caused by shear connections. It is shown that the same mechanism of coalescence is also relevant at volume fractions below 0.5 for systems in which the emulsion droplets are aggregated