NSF-BSF: From microscopic propulsion to macroscale dynamics: Active particle transport in complex environments

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Suspensions of self-propelled microparticles, or "microswimmers," whether biological or synthetic, have generated considerable interest over the last decade in a wide variety of disciplines, from biophysics to materials science to engineering. From a biological standpoint, understanding locomotion strategies of microswimmers is relevant to reproduction, the spread of disease and contamination processes in the environment. In engineering, active microparticles have been designed to transport material on small scales and to actuate gears and other devices. Nevertheless, the widespread use of microswimmers in practical applications is limited by an incomplete understanding of their propulsion strategies, interactions with their environment, and macroscale transport properties. This project, which is a collaboration between University of California - San Diego and the Technion, will use mathematical modeling and numerical simulations to enhance fundamental understanding of active particle transport in complex environments and geometries and the relationships between microscale propulsion and macroscale transport and hydrodynamics. This project will also support educational and outreach activities by engaging graduate and undergraduate students in the research, by incorporating the research in courses at UCSD and the Technion, and by presenting a summer introductory course on fluid mechanics for high-school students.This project will apply a combination of mathematical modeling and high-fidelity numerical simulations to address outstanding problems related to propulsion mechanisms, effective transport, and large-scale dynamics of microswimmers and their suspensions. The project will examine propulsion modalities of autophoretic colloids and will improve on existing models of self-diffusiophoretic propulsion by elucidating the effects of solute convection and relaxation, particle shape and interactions with rigid or soft boundaries. The team will also develop statistical models of microswimmer transport by using macrotransport theory and mean-field modeling to investigate long-time transport properties of self-propelled swimmers in channels as well as periodic porous media in both dilute and semi-dilute systems. Finally, the project will connect its themes by developing statistical descriptions of phoretic swimmers for problems where the phoretic mechanism and statistics of transport are coupled.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.