Surfactant Effects on Viscous Interactions of Drops


Surfactant Effects on Viscous Interactions of Drops

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.

This group is preparing for publication a review of collision efficiency calculations for raindrops that used MSI. Research on slightly deformable drops interacting in gravitational motion with partially mobile interfaces, which was presented at the APS-DFD meeting in Boston in November 2015, will be extended to nearly immobile interfaces in 2016. In addition, the group plans to begin research on slightly deformable drops in combined gravitational and thermocapillary motion in 2016. The primary objective 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.

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