Colloid motion is altered by adsorption to fluid interfaces, allowing for boundary guidance or directed assembly. This is particularly interesting for colloidal motion driven by external fields (driven colloids) or for self-propelled objects (active colloids or swimmers). However, the influence of a fluid interface on these hydrodynamic phenomena is relatively unexplored. We theoretically quantify the flows generated by interfacially trapped colloids by developing an appropriate flow singularity model for both driven and active colloids. The Reynolds and capillary numbers are assumed small, as is typical for colloidal systems involving an air- or oil-water interface, so interface deformation is neglected. We consider an ideal “clean” interface characterized solely by a uniform interfacial tension. We also consider an incompressible fluid interface, as can occur even for trace surfactant adsorption. Theoretical results are compared with experimental flow fields generated by (1) a microbead undergoing thermal motion, (2) a magnetic disk forced to translate at constant velocity, and (3) actively swimming <i>P. Aeruginosa</i> bacteria. Our results will be useful in future work on the use of active colloids to direct and enhance transport at interfaces.

Fluid motion induced by driven and active colloids at interfaces

Macromolecular Chemistry: The Second Century

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ACS Spring 2020 National Meeting & Expo

The official archive and repository for all ACS Meetings & Expositions abstracts and select posters or presentations.