title: Two spheres translating in tandem through a colloidal suspension.
abstract: Using laser tweezers, two colloidal particles are held parallel to a uniformly flowing suspension of similarly sized bath particles at an effective volume fraction ϕ(eff)=0.41. The local deformation in the bath suspension is imaged by confocal microscopy, and, concurrently, the drag forces exerted on both the leading and the trailing probe particles are measured as a function of probe separation and velocity. The bath structure changes in response to the velocity and separation of the probes. A depleted region between probes is observed at sufficiently high velocities. Both probes experience the same drag force and the drag force increases with probe separation. The results indicate that bath-probe and probe-probe hydrodynamic interactions contribute microstructure and drag force and that drag exerted by direct bath-probe collisions is reduced compared to an isolated probe.
authors.affiliation: Department of Chemical and Biomolecular Engineering, Center for Molecular and Engineering Thermodynamics, University of Delaware, Newark, Delaware 19716, USA.
authors.forename: Indira
authors.initials: I
authors.lastname: Sriram
authors.affiliation: Department of Chemical and Biomolecular Engineering, Center for Molecular and Engineering Thermodynamics, University of Delaware, Newark, Delaware 19716, USA.
authors.forename: Eric M
authors.initials: EM
authors.lastname: Furst