Dresden 2011 – wissenschaftliches Programm

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DY: Fachverband Dynamik und Statistische Physik

DY 43: Soft Matter

DY 43.1: Vortrag

Freitag, 18. März 2011, 10:15–10:30, ZEU 118

Mobility and Diffusion of a Tagged Particle in a Driven Colloidal Suspension — •Boris Lander¹, Udo Seifert¹, and Thomas Speck^{2, 3} — ¹II. Institut für Theoretische Physik, Universität Stuttgart, Pfaffenwaldring 57, 70550 Stuttgart, Germany — ²Department of Chemistry, University of California, Berkeley, California 94720, USA — ³Chemical Sciences Division, Lawrence Berkeley National Laboratory, Berkeley, California 94720, USA

Mobility and diffusion of single particles play a key role in the understanding of colloidal suspensions. While beyond linear response, diffusion coefficients can still be obtained by a Green-Kubo relation, determining the mobility is challenging. A novel method enables us to compute the time-dependent response function for a single tagged particle perturbed by a small force and thus the mobility in a Brownian dynamics simulation [1]. For a suspension driven into a nonequilibrium steady state by simple shear flow, both mobility and diffusion constant of the tagged particle increase with shear. Our data can be approximated by an expansion, where the mobility becomes proportional to the square root of the strain rate. Somewhat surprisingly, the initial decay of the velocity autocorrelation function can be mapped onto a corresponding response function by a time-independent scaling factor, allowing for an interpretation in terms of an ’effective temperature’. Such a phenomenological effective temperature recovers the Einstein relation in nonequilibrium.

[1] B. Lander, U. Seifert, T. Speck, EPL, in press.