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CPP: Chemische Physik und Polymerphysik

CPP 7: SYMPOSIUM Disperse Polymer Systems I

CPP 7.5: Hauptvortrag

Dienstag, 28. März 2006, 11:00–11:30, ZEU 160

Non-linear rheological properties of glassy colloidal dispersions — •Matthias Fuchs¹, Oliver Henrich¹, Michael Cates², Matthias Ballauff³, Jerome Crassous³, and Fathollah Varnik⁴ — ¹Fachbereich Physik, Universitaet Konstanz — ²School of Physics, The University of Edinburgh — ³Physikalische Chemie I, Universitaet Bayreuth — ⁴MPI fuer Eisenforschung, Duesseldorf

Soft materials, such as particle dispersions, quite universally exhibit a strongly decreasing viscosity as function of shear rate (’shear thinning’). We study theoretically an universal mechanism explaining the reduction of the viscosity or stress in such disordered colloidal systems.

Our first-principles approach [1] to the non-linear rheology of dense colloidal suspensions predicts an universal transition between the yielding of amorphous solids and non-Newtonian (shear-thinning) fluid flow. The approach builds upon a microscopic description of structural relaxations in quiescent suspensions provided by the mode coupling theory. The advection of density fluctuations is the dominant mechanism captured, while hydrodynamic interactions, non-linear flow profiles and ordering phenomena are neglected. Comparisons with experiments in model colloidal dispersions support the approach [2], as do computer simulations of Newtonian supercooled liquids, which find a finite dynamic yield stress at low temperatures [3].

[1] M. Fuchs and M. E. Cates, Phys. Rev. Lett. 89, 248304 (2002); Faraday Discuss. 123, 267 (2003); J. Phys.: Condens. Matter 17, 1681 (2005)

[2] M. Fuchs and M. Ballauff, J. Chem. Phys. 122, 094707 (2005)

[3] F. Varnik and O. Henrich, submitted (2005)