The effect of insoluble surfactant at dilute concentration on drop breakup under shear with inertia

Direct numerical simulations are conducted with a volume-of-fluid continuous surface stress algorithm. The linear equation of state is used to characterize the effects of an insoluble surfactant at low concentration on a drop in strong shear. The drop and the surrounding liquid have the same viscosity and density. Surfactant migration induces a Marangoni force that acts toward the drop center. For low inertia, viscous force opposes the Marangoni force, so that a stationary drop with surfactant is more elongated and less tilted than without. The addition of surfactant promotes breakup, lowering the critical capillary number. The first daughter drops are smaller than for the case of clean drops. For high inertia, the Marangoni force retracts the drop and retards breakup. The local values of surface tension are computed during drop evolution. (C) 2004 American Institute of Physics.