J. Phys. II France
Volume 4, Numéro 4, April 1994
Page(s) 555 - 560
DOI: 10.1051/jp2:1994146
J. Phys. II France 4 (1994) 555-560

Friction coefficient of rod-like chains of spheres at very low Reynolds numbers. I. Experiment

K. Zahn, R. Lenke and G. Maret

High Magnetic Field Laboratory, Max-Planck Institut für Festkörperforschung and Centre National de la Recherche Scientifique, B.P. 166, F-38042 Grenoble Cedex 9, France

(Received 30 November 1993, received in final form 11 February 1994, accepted 18 February 1994)

We present a new method to measure hydrodynamic friction forces on colloidal particles at very low ( $\simeq 10^{-5}$) Reynolds numbers with high accuracy. Exploiting magnetic field induced aggregation of microscopic paramagnetic spheres into straight chains of calibrated length, we determine the anisotropic friction coefficient of the chains, with a range from one to 100 particles, by video-microscopic observation of sedimentation speed. The results are found to agree well with the Slender-body theory, even for small chain lengths. The effects of the proximity of a wall are also explored.

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