Paper Number
GG2 

Session
Out of Equilibrium Systems: Gels and Glasses

Title
Investigation of the yielding transition in concentrated colloidal systems via rheo-XPCS

Presentation Date and Time
October 21, 2019 (Monday) 10:15

Track / Room
Track 7 / Room 306C

Authors (Click on name to view author profile)

1. Donley, Gavin J. (University of Illinois at Urbana-Champaign, Department of Chemical and Biomolecular Engineering)
2. Park, Jun Dong (University of Illinois at Urbana-Champaign, Department of Chemical and Biomolecular Engineering)
3. Wade, Matthew A. (University of Illinois at Urbana-Champaign, Department of Chemical and Biomolecular Engineering)
4. Naranayan, Suresh (Argonne National Laboratory, X-ray Sciences Divison)
5. Leheny, Robert L. (Johns Hopkins University, Department of Physics and Astronomy)
6. Harden, James L. (University of Ottawa, Department of Physics)
7. Rogers, Simon A. (University of Illinois at Urbana-Champaign, Department of Chemical and Biomolecular Engineering)

Author and Affiliation Lines (in printed abstract book)
Gavin J. Donley¹, Jun Dong Park¹, Matthew A. Wade¹, Suresh Naranayan², Robert L. Leheny³, James L. Harden⁴, and Simon A. Rogers^1
1Department of Chemical and Biomolecular Engineering, University of Illinois at Urbana-Champaign, Urbana, IL 61801; ²X-ray Sciences Divison, Argonne National Laboratory, Argonne, IL 60439; ³Department of Physics and Astronomy, Johns Hopkins University, Baltimore, MD 21218; ⁴Department of Physics, University of Ottawa, Ottawa, Ontario K1N 6N5, Canada

Speaker / Presenter 
Donley, Gavin J.

Text of Abstract
We probe the microstructural yielding dynamics of a concentrated colloidal system by performing creep/recovery and shear/recovery tests with simultaneous collection of scattering data via X-ray Photon Correlation Spectroscopy (XPCS). The combination of rheology and dynamics from scattering allows for time-resolved observations of the microstructure as yielding occurs, which can be linked back to the applied rheological deformation. To more accurately track the non-equilibrium processes which occur under yielding, we make use of two-time correlation functions, which provide additional time-resolved information that is inaccessible via more typical one-time correlations. The data suggest that yielding in these materials is triggered by a limitation in the acquisition of recoverable strain. In cases below the yield point, the scattering response recorrelates with its pre-deformed state, indicating that the microstructure recovers nearly-completely. By investigating the nature and extent of these recorrelations we can track the progress of the yielding transition. Examination of the correlation in the flow direction shows that larger creep stresses increase the speed of the dynamics, both during the application of creep and recovery intervals.