Kendra V. Sharp

Doublets of 48-μm-diameter polystyrene latex particles are experimentally tracked in a Poiseuille flow in a capillary tube. The rotational motion of nine doublets is observed using video microscopy with a translating stage. The particle diameter to capillary diameter ratio is 0.17, volume concentration 0.5%, and Reynolds number approximately 0.5. The rotational motions of the “large” particulate doublets are compared with theory originally developed for doublets with particle-to-tube diameters of the order of 0.04; the doublet rotations in the present experiments agree reasonably well with the earlier theory when the shear rate for the large doublet is defined based on the location of the centroid of shear rather than the shear rate at the radial center of mass of the rotating doublet. Additionally, these doublets are readily classified as primary or secondary on the basis of the rotational period.

The transient electrophoretic motion of a cylindrical particle through a relatively narrow channel is numerically simulated. The particle is initially located on the channel centerline and the initial angle of the particle to the channel centerline is varied with the objective of determining the effect on the particle trajectory. It is observed that the particles that begin aligned with or perpendicular to the channel centerline translate at a constant rate without rotation. The particles that begin at an intermediate angle (22.5°, 45°, and 67.5°) translate along the channel while also translating perpendicular to the channel centerline and rotating in an oscillatory manner.