title: Comparison of Faxén's correction for a microsphere translating or rotating near a surface.
abstract: Boundary walls in microfluidic devices have a strong influence on the fluid flow and drag forces on moving objects. The Stokes drag force acting on a sphere translating in the fluid is increased by the presence of a neighboring wall by a factor given by Faxén's correction. A similar increase in the rotational drag is expected when spinning close to a wall. We use optical tweezers to confirm the translational drag correction and report the hitherto unmeasured rotational equivalent. We find that the corrections for the rotational motion is only required for particle-wall separations an order of magnitude shorter than that for the translational cases. These results are particularly significant in the use of optical tweezers for measuring viscosity on a picolitre scale.
authors.affiliation: Department of Physics and Astronomy, University of Glasgow, Glasgow, Scotland. j.leach@physics.gla.ac.uk
authors.forename: J
authors.initials: J
authors.lastname: Leach
authors.forename: H
authors.initials: H
authors.lastname: Mushfique
authors.forename: S
authors.initials: S
authors.lastname: Keen
authors.forename: R
authors.initials: R
authors.lastname: Di Leonardo
authors.forename: G
authors.initials: G
authors.lastname: Ruocco
authors.forename: J M
authors.initials: JM
authors.lastname: Cooper
authors.forename: M J
authors.initials: MJ
authors.lastname: Padgett