Collaborative Research: Understanding Plasma-Liquid Interactions Through Controlled Plasma-Microdroplet Experiments and Modeling

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This collaborative research project between University of Minnesota-Twin Cities and University of Michigan-Ann Arbor will study the interaction of a water droplet with an atmospheric pressure plasma - a reactive gas of neutral atoms and molecules, charged radicals and ions, and electrons. Chemically reactive liquids are used throughout society, from cleaning fluids in the home to customized solutions for pharmaceutical manufacturing; and now increasingly in biomedical applications. Customizing the reactivity of these liquids is a challenge, particularly when the active species have short lifetimes. Atmospheric pressure plasmas are an ideal medium to produce chemical reactivity; and plasma-liquid interactions leverage the ability to generate chemically reactive species in plasmas to produce unique chemical reactivity in the liquid. This project will also develop and support an annual one-week US Low Temperature Plasma School aimed to provide opportunities for graduate students from across the country to be immersed in low temperature plasma science and learn from leading researchers in their field.In this research project, the interaction of a single water droplet with a controlled diffuse cold atmospheric pressure plasma will be investigated with the goal of quantifying the reaction of plasma produced species with liquids. The reaction kinetics occurring near the boundary between the gas plasma and liquid, resulting in interfacial transport, becomes increasingly complex when transport and reactivity are highly coupled. This is often the case when transport includes short-lived highly reactive species as in both the plasma and liquid phases, and species transfer is transport limited. Plasma activation of aerosols and small liquid droplets interspersed in the gas plasma provides opportunities to reduce transport limits to a minimum. The experimental apparatus at University of Minnesota will uniquely enable the investigation of plasma interactions with a single droplet of known initial and final composition, passing through a well-characterized plasma. Multi-phase plasma modeling at University of Michigan will comprehensively address this complex system. The anticipated results will, in particular, elucidate droplet charging, plasma induced droplet evaporation, transport mechanisms of short-lived species and convective transport effects.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.