Dynamic behaviors of surfactant-containing droplets under a uniform electric field

This paper adopts the phase-field based lattice Boltzmann (LB) method to study the dynamic behaviors of soluble surfactant-laden droplets in a uniform electric field. First, two benchmark problems including the surfactant concentration distribution on a static droplet and the deformation of a leaky dielectric droplet in an electric field, are used to validate the reliability of the LB method. Then, we investigate the deformation, breakup, and coalescence behaviors of surfactant-laden droplets in an electric field. The obtained results are shown below. 1) Regarding deformation, the single droplet exhibits two distinct deformation modes: Prolate and oblate shapes. A higher electric capillary number and a higher concentration of bulk surfactants both promote greater droplet deformation. 2) Regarding breakup, a single droplet exhibits two distinct breakup modes: filamentous breakup and conical jetting breakup. Droplets containing surfactants are more like to break up. Specifically, surfactants reduce the retraction degree of the main droplet after filamentous breakup, while increasing the number of satellite droplets formed at the ends of the main droplet after jetting breakup. 3) Regarding coalescence, the double droplets exhibit two distinct processes: deformation coalescence and attractive coalescence. A higher electric capillary number facilitates droplet coalescence. Surfactants promote the deformation coalescence while retarding attractive coalescence, but the promotional effect dominates. Consequently, a higher concentration of bulk surfactants will enhance the tendency of droplet coalescence.