How depletion affects sphere motion through solutions containing macromolecules

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: 24 July 2006

Abstract

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.