How depletion affects sphere motion through solutions containing macromoleculesR. 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