title: A numerical investigation on the drainage of a surfactant-modified water droplet in paraffin oil.
abstract: A volume of fluid approach is used in numerical simulations of the settling motion of a surfactant modified water droplet in a continuous paraffin oil phase. The droplet is millimeter-sized and confined in a square two dimensional domain. The surfactant interfacial and bulk concentration-equations are solved together with the incompressible Navier-Stokes equation. The role of boundary walls in the overall settling dynamics is described. As the droplet moves downwards the interfacial shear creates non-homogeneous interfacial surfactant concentrations and Marangoni driven phenomena come into play. A decrease of the drainage velocity is then evidenced indicating that buoyancy forces are counter balanced by Marangoni induced lift-forces. The lateral migration of the droplet due to boundary wall proximity is discussed. It is shown to increase with wall proximity and to decrease when increasing the interfacial concentration. Finally, a simplified model is used to investigate the evolution of the bulk concentration assuming the surfactant is insoluble in paraffin oil and poorly soluble in water.
authors.affiliation: Aix-Marseille Université, CNRS, MADIREL UMR 7246, 13397 Marseille, France.
authors.forename: Adil
authors.initials: A
authors.lastname: Lekhlifi
authors.affiliation: Aix-Marseille Université, CNRS, MADIREL UMR 7246, 13397 Marseille, France.
authors.forename: Abdelaziz
authors.initials: A
authors.lastname: Fanzar
authors.affiliation: Aix-Marseille Université, CNRS, MADIREL UMR 7246, 13397 Marseille, France.
authors.forename: Mickaël
authors.initials: M
authors.lastname: Antoni
keywords: Droplets; Marangoni and buoyancy-driven flows; Multiphase flows; Simulation