Berlin 2008 – scientific programme

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CPP: Fachverband Chemische Physik und Polymerphysik

CPP 16: SYMPOSIUM Driven Soft Matter I

CPP 16.7: Talk

Tuesday, February 26, 2008, 12:00–12:15, C 130

A binary Yukawa mixture under shear: A computer simulation study of the transient dynamics — •Jochen Zausch¹ and Jürgen Horbach² — ¹Inst. f. Physik, Universität Mainz, Staudinger Weg 7, 55099 Mainz — ²Inst. f. Materialphysik im Weltraum, DLR, Linder Höhe, 51147 Köln

Very recently, experiments and computer simulations have demonstrated that shear strongly affects transport properties of an undercooled liquid. If the shear rate γ exceeds the typical relaxation time τ of the system, an acceleration of the dynamics is observed which is reflected, e.g., in a decrease of the shear viscosity (shear thinning). The underlying mechanism of this change is still not well understood on a microscopic level.

We use extensive molecular dynamics simulations to elucidate the transient dynamics of a sheared binary Yukawa mixture from equilibrium to steady state, after a constant shear field is switched on. By inspection of the density-density correlation function we find that the steady state is reached after a time of the order of γ⁻¹. The same is true for the stress that is built up upon increasing strain. The linear velocity profile on the other hand develops in a much shorter time. Similar simulations are performed for the case when a sheared system falls back to equilibrium after shear is switched off. Interestingly, the stress decays as fast as it was built up although the system is still far from equilibrium.