Berlin 2015 – scientific programme

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CPP: Fachverband Chemische Physik und Polymerphysik

CPP 73: Focus: Disordered Systems/Glasses under Shear (joint session CPP, DY)

CPP 73.4: Talk

Thursday, March 19, 2015, 16:30–16:45, C 243

Yielding in concentrated colloidal dispersions: relation between stress overshoot and microscopic structure and dynamics — Marco Laurati, Kevin Mutch, and •Stefan Egelhaaf — Condensed Matter Physics Laboratory, Heinrich Heine University, 40225 Düsseldorf, Germany

The microscopic structure and dynamics of concentrated colloidal dispersions at different times after application of shear is determined using confocal microscopy. When the stress overshoot occurs in the rheological response, we observe super-diffusion and a maximally deformed cage, i.e. maximum structural anisotropy [1,2]. The anisotropy is not only characterized by a quadrupolar (angular momentum l = 2) distortion expected by continuum elasticity theory, but also a higher order hexadecupolar (l = 4) mode which marks the transition form reversible elastic to irreversible plastic deformation [3]. This mode suggests that yielding of local cages proceeds through the rearrangement of particles in the first neighbour shells, which switch from the compressional to the extensional axis. Also in the steady-state of shear, cage-breaking events are found to persist. In addition to the anisotropic cage deformation, yielding is also accompanied by a strong rise in the isotropic (l = 0) distortion, which corresponds to a pressure increase.

[1] N. Koumakis et al. (2012) Phys. Rev. Lett. 108, 098303. [2] K.J. Mutch et al. (2013) Eur. Phys. J. - Special Topics 222, 2803. [3] C.P. Amann et al. (2013) arxiv:1302.2030.