Active Fluids in Externally Driven Flows

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This research will develop the theoretical framework for the design and control of active fluids. Active fluids are driven by energy which is added at the small scale of the particles that make up the fluid. For example, the cytosol in our cells flows because molecular motors consume energy-storing ATP molecules and use this energy to slide rigid biopolymers past each other. This sliding motion induces flows that can be used for cell crawling or the transport of biological materials within the cell. There is currently great interest in developing artificial active matter systems, such as a microfluidic device which pumps itself. Understanding the hydrodynamic properties of active fluids is essential if they are ever to be of practical use in medicine or industry. The focus of this research is to mathematically model the flow of an active fluid when it is subject to an externally driven flow, such as the flow driven by a pump. The results of theoretical calculations will be compared with experiments to determine the parameters that control the nature of active flow. This research will support the scientific training of undergraduate and graduate students. The PIs will mentor undergraduates from historically underrepresented groups in engineering and physical science through the Leadership Alliance Summer Research Early Identification Program. Topics related to this work will be integrated into undergraduate and graduate courses in engineering and physics. There are very few studies of active matter subject to external flows. The goal of this research is to study the fluid dynamics of active gels, i.e. active apolar filaments that are sufficiently dilute that they tend not to spontaneously align and form a liquid crystalline phase. Linear stability analysis and numerical computation will be used to study the activity-driven flow transitions in active gels in two dimensions subject to external flows of Couette, Poiseuille, and Taylor-Couette types. Simulations will be used to explore the effect of confinement on active gels in lid-driven cavity flow. Finally, three-dimensional channel flows of active gels will be studied, as well as the drag forces and torques and spontaneous motion of objects in an active gel.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.