Europhys. Lett.
Volume 75, Number 6, September 2006
Page(s) 929 - 935
Section Condensed matter: structural, mechanical and thermal properties
Published online 09 August 2006
Europhys. Lett., 75 (6), pp. 929-935 (2006)
DOI: 10.1209/epl/i2006-10200-0

How depletion affects sphere motion through solutions containing macromolecules

R. Tuinier1, J. K. G. Dhont1 and T.-H. Fan2

1  Forschungszentrum Jülich, Institut für Festkörperforschung 52425 Jülich, Germany
2  Department of Mechanical Engineering, University of Connecticut Storrs, CT 06269-3139, USA

received 20 March 2006; accepted in final form 24 July 2006
published online 9 August 2006

We present analytical expressions for the friction a sphere experiences when it moves through a macromolecular medium, showing the friction is strongly reduced compared to Stokes' law due to an entropic depletion effect. Depletion of macromolecules from the sphere surface leads to a low-viscosity layer around the sphere as compared to the viscosity in the crowded bulk. The resulting translational and rotational transport behaviour of a sphere through a polymer solution was analytically resolved using Stokes' stream function theory, showing the spheres apparently slip in the crowded medium of macromolecules. This slip facilitates particle diffusion.

66.20.+d - Viscosity of liquids; diffusive momentum transport.
87.14.Ee - Proteins.
82.70.Dd - Colloids.

© EDP Sciences 2006