Session MB - Drops I. Emulsions & Drops.
MIXED session, Tuesday afternoon, November 23
Grand II, Westin Seattle
Surfactants modify interfacial properties and significantly affect drop behavior in flow. We study dynamics a drop, which is covered with a dilute monolayer of insoluble surfactant, in linear viscous flows, both unbounded and in the presence of a wall. The problem is challenging because of the nonlinear coupling of drop deformation, surfactant redistribution, and bulk flows. Analytical expansions applicable where the surfactant distribution and drop shape are only slightly perturbed from their equilibrium state are developed. Numerical results, including three-dimensional boundary integral simulations are used to determine the range of convergence for the expansions. The theoretical analyses quantify the interplay between the restoring mechanisms (Marangoni-- and shape-- relaxation, and drop rotation by the imposed flow) and the distortion of surfactant distribution and drop shape induced by the straining component of the flow. Studies of the hydrodynamic interactions of a surfactant-covered drop with a wall show that nonuniform surfactant distribution causes a spherical drop to migrate away from the wall. Calculations of the stress in a dilute emulsion of surfactant-covered drops reveal rich rheological behavior.