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Connecting structure, dynamics and viscosity in sheared soft colloidal liquids: a medley of anisotropic fluctuations

DOI: 10.1039/C5SM01707F DOI Help
PMID: 26451659 PMID Help

Authors: Fabian Westermeier (Max Planck Institute for the Structure and Dynamics of Matter) , David Pennicard (DESY) , Helmut Hirsemann (DESY) , Ulrich Wagner (Diamond Light Source) , Christoph Rau (Diamond Light Source) , Heinz Graafsma (DESY) , Peter Schall (University of Amsterdam) , Minne Paul Lettinga (Forschungszentrum J├╝lich GmbH) , Bernd Struth (DESY)
Co-authored by industrial partner: No

Type: Journal Paper
Journal: Soft Matter

State: Published (Approved)
Published: October 2015

Abstract: Structural distortion and relaxation are central to any liquid flow. Their full understanding requires simultaneous probing of the mechanical as well as structural and dynamical response. We provide the first full dynamical measurement of the transient structure using combined coherent X-ray scattering and rheology on electrostatically interacting colloidal fluids. We find a stress overshoot during the start-up of shear which is due to the strong anisotropic overstretching and compression of nearest-neighbor distances. The rheological response is reflected in uncorrelated entropy-driven intensity fluctuations. While the structural distortion under steady shear is well described by Smoluchowski theory, we find an increase of the particle dynamics beyond the trivial contribution of flow. After the cessation of shear, the full fluid microstructure and dynamics are restored, both on the structural relaxation timescale. We thus find unique structure-dynamics relations in liquid flow, responsible for the macroscopic rheological behavior of the system.

Subject Areas: Chemistry, Materials

Instruments: I13-1-Coherence

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