Active emulsions: Magneto-capillary dynamics of particles at curved interfaces award

Oil and water don?t mix; however, by stabilizing the interface between them, small droplets of one can be dispersed in the other. These so-called emulsions are commonly found in foods, cosmetics, and pharmaceuticals where mixtures of oil-loving and water-loving molecules must work together to function properly. Surface-active molecules and particles - termed surfactants - adsorb at oil-water interfaces to stabilize emulsions and prevent unmixing. This project aims to create magnet surfactants that use external magnetic fields to power dynamic functions such as mixing and propulsion at the level of individual emulsion droplets. The project will investigate the magnetically driven motions of particles adsorbed at curved interfaces and their use in pumping fluids at the micron-scale. The resulting active emulsions are potentially important for accelerating and/or controlling the rates of drug delivery or chemical reactions within complex fluids. In addition to research training for graduate and undergraduate students, the project will provide educational outreach to middle and high school students from diverse backgrounds. In collaboration with the Inside Engineering initiative, the researchers will develop and implement a laboratory visit curriculum for students from nearby schools in Manhattan and the Bronx. Through hands-on demonstrations and active learning strategies, the program aims to get students excited about the processes of scientific inquiry and engineering design.

Rapid particle motions in uniform fields are made possible by coupling magnetic torques to capillary forces at curved interfaces. Building on recent demonstrations of these magneto-capillary dynamics, the project will investigate how time-varying magnetic fields can drive complex particle motions and interfacial flows within and around liquid droplets. The project aims (1) to understand how the waveform of the driving field and the properties of the magnetic particles direct their dynamic motions on curved interfaces; (2) to quantify the transient fluid flows within and around emulsion droplets induced by particle motions; and (3) to identify specific particle types and driving protocols optimized for desired functions such as enhancing mass transfer and propelling droplet motions. These aims will be achieved through a combination of experiments on particle/emulsion systems and modeling of magneto-capillary particle dynamics and fluid flows. The project will examine how these field induced flows can be harnessed for enhancing mass transfer and for propelling drop motions. In contrast to bulk processing of macroscopic emulsions, distributed actuation within active emulsions will enable new strategies for engineering reaction kinetics, mass transport, and separations within multiphase fluids. In pursuit of these functions, automated tools for Bayesian inference, experimental design, and optimization will be developed and deployed to enable the efficient exploration of possible driving fields.

This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.