Regensburg 2016 – wissenschaftliches Programm

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CPP: Fachverband Chemische Physik und Polymerphysik

CPP 12: Poster: Colloids and Complex Fluids

CPP 12.4: Poster

Montag, 7. März 2016, 18:15–21:00, Poster B2

Discontinuous thinning behavior in active microrheology of attractive colloids — •Robert Wulfert¹, Udo Seifert¹, and Thomas Speck² — ¹II. Institut für Theoretische Physik, Universität Stuttgart, Germany — ²Institut für Physik, Johannes Gutenberg-Universität Mainz, Germany

Arguably the most exciting phenomena in traditional macrorheology hinge on the non-linear response of complex fluids to external flows. In extreme cases, non-linear flow curves can even comprise discontinuities, as in the paradigmatic example of cornstarch suspensions, which solidify abruptly when exceeding a certain critical strain-rate. Active microrheology (AMR) has established itself rather recently as a complementary approach to infer viscoelastic properties of complex media by driving an embedded colloidal probe and tracing its microscopic trajectory. Although the existence of an exact relation between micro- and macrorheology remains an open issue, AMR has qualitatively reproduced quintessential properties like the thinning and thickening of colloidal soft-matter under flow. Based on the well-established simple-paradigm model for AMR, we report on discontinuous force-thinning of colloidal suspensions with attractive long-range interactions: At a critical force, the suspensions microviscosity drops abruptly by about an order of magnitude. By complementing numerical solutions of the pair-Smoluchowski equation with Brownian-dynamics simulations, hysteretical behavior around this critical force is revealed for finite-time force protocols.