The end-pinching mechanism for surfactant-laden multiphase flows*

The presence of surfactants in any multiphase flow system often reduces the local value of surface tension but it also generates tangential stress at the interface due to the surfactant interfacial gradient known as Marangoni stress. Depending on the prevailing flow fields, these stresses can act to rigidify the interface and inhibit droplet end-pinching particularly if they dominate inertia. We will present through this talk different examples of end-pinching mechanisms that have recently been studied such as in retracting ligaments, bursting bubbles, and drop coalescence. The results that will be discussed were generated via three-dimensional simulations using a hybrid interface-tracking/level-set approach that accounts for variations in surfactant interfacial concentrations coupled to the flow dynamics; this methodology is capable of capturing accurately changes in interfacial topology.