The term “surfactant” is short for "surface-active agents," like soap. Surfactants reside at the interface between two liquids, or a liquid and a gas, and modify the interfacial tension between the phases. The presence of surfactant affects the interactions between drops in an immiscible medium, including whether or not the drops coalesce. These interactions are important in emulsion stability, sedimentation and creaming, polymer blending, rheology, liquid-liquid extraction, and geophysical flows. Thus, understanding how surfactants work is important to many industries, including food, pesticides, paints, ore flotation, and detergents.
The primary objective of this research is to develop a fundamental understanding of the role of surfactants in dilute dispersions of spherical and deformable drops in a variety of flows. Analytical and semi-analytical methods are used for two spherical drops in the presence of surfactant, while boundary-integral methods are employed for two moderately deformable drops. In general, the goal is to calculate collision efficiencies for spherical drops, or breakup and capture efficiencies for deformable drops, by a trajectory analysis. The behavior of dilute dispersions can then be predicted through population dynamics simulations.
Work carried out with supercomputing resources includes:
- A review of collision efficiency calculations with preliminary results for raindrops
- Research on slightly deformable drops in combined gravitational and thermocapillary motion
- Continuing work on small, contaminated drops in combined gravitational and thermocapillary motion at finite Stokes numbers with emphasis on nonlinear phenomena; this work should be completed by the end of 2020
- New work on interactions of surfactant-covered drops with differing densities and thermal conductivities, with application to particle scavenging by raindrops, is being mapped out for 2020