Mobility and diffusion of a tagged particle in a driven colloidal suspension

¹ II. Institut für Theoretische Physik, Universität Stuttgart - Pfaffenwaldring 57, 70550 Stuttgart, Germany, EU
² Department of Chemistry, University of California - Berkeley, CA 94720, USA
³ Chemical Sciences Division, Lawrence Berkeley National Laboratory - Berkeley, CA 94720, USA

Received: 23 September 2010
Accepted: 17 November 2010

Abstract

We study numerically the influence of density and strain rate on the diffusion and mobility of a single tagged particle in a sheared colloidal suspension. We determine independently the time-dependent velocity autocorrelation functions and, through a novel method, the response functions with respect to a small force. While both the diffusion coefficient and the mobility depend on the strain rate the latter exhibits a rather weak dependency. Somewhat surprisingly, we find that the initial decay of response and correlation functions coincide, allowing for an interpretation in terms of an “effective temperature”. Such a phenomenological effective temperature recovers the Einstein relation in nonequilibrium. We show that our data is well described by two expansions to lowest order in the strain rate.