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ICS-3 Group seminar
Complex yielding in frustrated states of attractive colloids

Prof. Dr. George Petekidis

IESL-FORTH & Materials Science & Technology Department, University of Crete, Heraklion, Greece.


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19 Dec 2017 10:30
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19 Dec 2017 11:30
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Seminarraum A1-3, Building 04.6, Entrance E1

Abstract:

I will present key microscopic mechanisms affecting the structure and particle dynamics when attractive interactions are added in a hard sphere glass.  Furthermore the effect of attractions in the macroscopic response of repulsive (hard-sphere) and attractive glasses during nonlinear rheology and yielding is studied by a combined experimental and computer simulation study.

I mainly focus on the way such systems yield under the application of steady or oscillatory shear via start-up shear tests and large amplitude oscillatory shear, as well as on the mechanisms of structural reformation and related stress relaxation after shear cessation. I discuss the phenomenology of two-step yielding, widely observed experimentally, its relation with quiescent microscopic dynamics and the underlying mechanisms affecting the relevant length- and time-scales during shear. 

Both experiments and Brownian Dynamics (BD) simulations show two peaks in stress versus strain during start-up shear tests with good qualitative agreement suggesting that Hydrodynamic Interactions are not crucially important at such highly concentrated systems. Structural analysis obtained from BD simulations confirms that the first yield is related to the breaking of the structure at the length scales smaller than attraction range while the second yield point is a consequence of cage deformation and breaking.

Contact

Prof. Jan K.G. Dhont
Phone: +49 2461 61-2160
Fax: +49 2461 61-2765
email: j.k.g.dhont@fz-juelich.de

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