CEMS Seminar - Dr. Kathleen (Kate) Stebe
Dr. Kathleen (Kate) Stebe, Goodwin Professor, Chemical and Biomolecular Engineering, University of Pennsylvania
Seminar title: "Active Surface Agents: Active colloids at fluid-fluid interfaces."
Fluid interfaces are highly non-ideal, complex domains that impose constraints that alter swimming behavior. We study the bacterium Pseudomonas Aeruginosa (PA01) at aqueous- hexadecane interfaces and characterize several distinct swimming behaviors. The bacteria can swim adjacent to the interface, or they can adsorb directly and swim in an adhered state with complex trajectories that differ from those in bulk in both form and spatio-temporal implications. We find that the adsorbed bacteria are trapped in the interface with pinned three phase contact lines that significantly constrain their motion. In addition, surfactant adsorption alters interfacial mechanics. For colloidal swimmers, stress conditions require that the interface be a 2-D incompressible fluid, restructuring interfacial flows. We measure the flow generated by these swimmers in the pusher mode using a recently developed flow visualization method correlated displacement velocimetry. We find a flow field with unexpected asymmetries. Hydrodynamic theory allows us to understand this flow field fundamentally and to explore its implications on mixing in the interface.
Our aim is to advance the concept of an Active Surface Agent, an active colloid trapped at fluid interfaces whose motion and trapping state can be designed to promote mixing and structure formation. This concept represents an important and largely untapped degree of freedom for interfacial engineering. By understanding how biological swimmers move at fluid interfaces, we can develop design rules for artificial biomimetic systems to promote transport at fluid interfaces with broad implications in chemical engineering processes.
Driven and Active Colloids at Interfaces Nicholas G. Chisholm and Kathleen J. Stebe, Volume 914 - 10 May 2021 Special JFM volume in celebration of the George K. Batchelor centenary
Interfacial Flow around Brownian Colloids, Mehdi Molaei, Nicholas G. Chisholm, Jiayi Deng, John C. Crocker, and Kathleen J. Stebe, Phys. Rev. Lett. 126, 228003
Interfacial flow around a pusher bacterium, in prep. Jiayi Deng, Mehdi Molaei, Nicholas G. Chisholm, Kathleen J. Stebe
Kathleen J. Stebe is the Goodwin Professor in the School Engineering and Applied Sciences at the University of Pennsylvania. Her research focuses on directed assembly in soft matter and at fluid interfaces. Trained at the Levich Institute under the guidance of Charles Maldarelli, she then spent a post-doctoral year in Compiegne, France under the guidance of Dominique Barthes-Biesel. Thereafter, she joined the faculty of the Department of Chemical Engineering at Johns Hopkins University, and later joined the Department of Chemical and Biomolecular Engineering at the University of Pennsylvania. She has been recognized by the National Academy of Engineering, the American Academy of Arts and Sciences, the Johns Hopkins Society of Scholars, as a Fellow of the American Physical Society and of the Radcliffe Institute. Dr. Stebe received her Ph.D. in Chemical Engineering at the City College of New York.