Chemical and Biomolecular Engineering School of Engineering and Applied Science University of Pennsylvania
Kathleen J. Stebe is the Goodwin Professor in the School Engineering and Applied Sciences at the University of Pennsylvania. Educated at the City College of New York, she received a B.A. in Economics and a Ph.D. in Chemical Engineering at the Levich Institute advised by Charles Maldarelli. After a post-doctoral year in Compiegne, France under the guidance of Dominique Barthes-Biesel, she joined the Department of Chemical Engineering at Johns Hopkins University, where she became Professor and served as the department chair. Thereafter, she joined the University of Pennsylvania, where she served in various administrative capacities including department chair and Deputy Dean. She has been recognized by the National Academy of Engineering, the American Academy of Arts and Sciences, the Johns Hopkins Society of Scholars, and as a Fellow of the American Physical Society and of the Radcliffe Institute. Her research focuses on directed assembly in soft matter and at fluid interfaces, with an emphasis on confinement, geometry, and emergent structures in far from equilibrium settings for novel functional materials.
We are advancing the concept of an Active Surface Agent, an active or self-propelled 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 product design. Fluid interfaces are highly non-ideal, complex domains that impose constraints that alter swimming behavior. We study the bacterium Pseudomonas Aeruginosa (PA01) at fluid interfaces and characterize several distinct swimming behaviors. 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 a swimmer at the interface in the pusher mode using a recently developed flow visualization method correlated displacement velocimetry and 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.