Berlin 2012 – scientific programme

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CPP: Fachverband Chemische Physik und Polymerphysik

CPP 12: Glasses II (joint session with DY)

CPP 12.8: Talk

Tuesday, March 27, 2012, 11:45–12:00, MA 004

Transient stresses and MSDs in sheared dispersions as described by mode-coupling theory (MCT) — •Christian Peter Amann and Matthias Fuchs — Fachbereich Physik, Universität Konstanz, 78457 Konstanz, Germany

Sheared viscoelastic media exhibit a stress overshoot between elastic and plastic regime, i.e. a maximum in the shear stress vs strain plot after switching on a constant shear rate. This maximum characterizes the transient evolution between equilibrium and steady state. A way to model such overshoots is the F₁₂^(γ) model, a schematic model in MCT to describe glass forming liquids. This approach is tested by comparing results with various rheological experiments. Flow curves, linear- and non-linear stress response, and stress-strain curves can be fitted consistently with the same model [1,2]. Within microscopic MCT the stress overshoot is identified as negative dip in the dynamic stress autocorrelation function [3].

This mechanism also causes super-diffusive colloid motion [3]. We connect shear stress and colloidal MSD via a generalized Stokes–Einstein relation and compare shear–stress and MSD simulations to define a characteristic strain determining maximum shear stress and onset of superdiffusion.

[1] M. Siebenbürger et al., J. Rheol. 53, 707–726 (2009)

[2] J.M. Brader et al., Phys. Rev. E 82, 061401 (2010)

[3] J. Zausch et al., J. Phys.: Condens. Matter 20, 404210 (2008)