Comparison of Faxén's correction for a microsphere translating or rotating near a surface.
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.
Leach
J
J
Department of Physics and Astronomy, University of Glasgow, Glasgow, Scotland. j.leach@physics.gla.ac.uk
Mushfique
H
H
Keen
S
S
Di Leonardo
R
R
Ruocco
G
G
Cooper
J M
JM
Padgett
M J
MJ