Debye Colloquium - Kathleen Stebe

Active Surface Agents: Active colloids at fluid-fluid interfaces

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Active Surface Agents figure
Active Surface Agents

The ability to control the stresses at fluid interfaces by adsorption of colloids or surfactants has been widely exploited in chemical engineering processes. What if we could trap swimmers on fluid interfaces? Would the interfaces be self-mixing? How would we describe the effects of these interfacial swimmers on processes like reactive diffusion at interfaces? 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.

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.

After the colloquium there will be drinks & snacks from 17:00h - 18:30h

 

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Pangea Hall, Victor J. Koningsbergergebouw
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