Two spheres translating in tandem through a colloidal suspension

Indira Sriram and Eric M. Furst

Using laser tweezers, two colloidal particles are held parallel to a uniformly flowing suspension of similarly sized bath particles at an effective volume fraction ϕeff=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.

DOI