Berlin 2012 – scientific programme
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CPP: Fachverband Chemische Physik und Polymerphysik
CPP 35: Focus: Rheology I (joint focus with DRG)
CPP 35.5: Talk
Thursday, March 29, 2012, 16:15–16:30, C 243
Nonlinear active micro-rheology of dense colloidal suspensions — •Thomas Voigtmann1,2,3, Matthias Fuchs1, Christian Harrer1, and Manuel Gnann1 — 1Fachbereich Physik, Universität Konstanz — 2Zukunftskolleg, Universität Konstanz — 3Institut für Materialphysik im Weltraum, Deutsches Zentrum für Luft- und Raumfahrt (DLR), 51170 Köln
Active microrheology is a powerful tool to probe the local dynamics and rheological properties of a complex material, monitoring the response to external driving applied to a tracer particle. Especially the nonlinear-response regime reveals a wealth of information, but is less obvious to analyze than the linear response. We present recent advances in the framework of mode-coupling theory and the integration-through-transients formalism for force-driven microrheology, applying a constant force to a probe embedded in a dense, glass-forming colloidal suspension. A typical signature seen in experiment and computer simulation is a pronounced force-thinning, i.e., a strong reduction of the local friction at forces large compared to those induced by thermal fluctuations. We discuss this nonlinear effect in terms of a delocalization transition for the probe particle. We also address the limit of strong driving, where a non-trivial high-force plateau in the probe’s friction coefficient is observed. Connections of these microscopic quantities to macroscopic rheological properties of the host liquid, and possible universalities among different system classes will also be discussed.
[1] I. Gazuz et al., Phys. Rev. Lett. 102, 248302 (2009).
[2] M. V. Gnann et al., Soft Matter 7, 1390 (2011).