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DY: Fachverband Dynamik und Statistische Physik

DY 39: Flow-Induced Structures in Complex Fluids (joint session CPP/ DRG, Deutsche Rheologische Gesellschaft/ DY)

DY 39.3: Vortrag

Mittwoch, 18. März 2015, 15:45–16:00, C 264

Microstructure and nonlinear signatures of yielding in a heterogeneous colloidal gel under large amplitude oscillatory shear — Juntae Kim¹, •Dimitri Merger², Manfred Wilhelm², and Matthew E. Helgeson¹ — ¹Department of Chemical Engineering, University of California Santa Barbara, Santa Barbara, California 93106 — ²Institute for Chemical Technology and Polymer Chemistry, Karlsruhe Institute of Technology, 76131 Karlsruhe, Germany

We investigate yielding in a colloidal gel that forms from a nanoemulsion by polymer mediated aggregation. Combining large amplitude oscillatory shear measurements with simultaneous small and ultra-small angle neutron scattering (rheo-SANS/USANS), we characterize both the nonlinear mechanical processes and strain amplitude-dependent microstructure underlying yielding. We observe a broad, three-stage yielding process that evolves over an order of magnitude in strain amplitude between the onset of nonlinearity and flow. Analyzing the intracycle response stress reveals a transition from elastic straining to elastoplastic thinning which eventually leads to yielding and flow. The instantaneous nonlinear parameters associated with yielding are correlated with time-averaged rheo-USANS measurements. This shows how the material passes through a cascade of structural breakdown from large to progressively smaller length scales. All significant structural changes occur on the micron-scale, suggesting that large-scale rearrangements of hundreds or thousands of particles, rather than the homogeneous rearrangement of particle-particle bonds, dominate the initial yielding of heterogeneous colloidal gels.