Paper Number
IN8 

Session
Flow-induced Instabilities and Non-Newtonian Fluids

Title
The specific sequence of physical processes that causes the loss modulus overshoot in yield stress fluids

Presentation Date and Time
October 12, 2021 (Tuesday) 4:35

Track / Room
Track 4 / Meeting Room C-D

Authors (Click on name to view author profile)

  1. Donley, Gavin J. (Georgetown University, Physics)
  2. Kamani, Krutarth M. (University of Illinois at Urbana-Champaign, Department of Chemical and Biomolecular Engineering)
  3. Singh, Piyush K. (University of Illinois at Urbana-Champaign, Department of Chemical and Biomolecular Engineering)
  4. Shetty, Abhishek (Anton Paar USA, Rheology)
  5. 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, Krutarth M. Kamani2, Piyush K. Singh2, Abhishek Shetty3 and Simon A. Rogers2
1Physics, Georgetown University, Washington DC, DC 20057; 2Department of Chemical and Biomolecular Engineering, University of Illinois at Urbana-Champaign, Urbana, IL 61801; 3Rheology, Anton Paar USA, Ashland, VA 23005

Speaker / Presenter 
Donley, Gavin J.

Keywords
experimental methods; theoretical methods; colloids; composites; gels; glasses; non-Newtonian fluids; polymer solutions; rheology methods

Text of Abstract
We gain a deeper understanding of the yielding transition by performing an experimental decomposition of the rheological response of simple yield stress fluids under oscillatory shearing. By iteratively performing recovery tests throughout the period, combining strain- and stress-controlled rheometry, the transience of the recoverable and unrecoverable strains is distinguished, allowing the solid-like and fluid-like contributions to the material’s behavior to be experimentally separated in a time-resolved manner. The decomposed strains allow for solid- and fluid-like contributions to G’’ to be defined which are both significant across the entire amplitude sweep. We specifically show that the gradual increase in the acquisition of strain unrecoverably at intermediate amplitudes is responsible for the overshoot in the loss modulus, which has been referred to as the Payne effect or a Type III response. We show that this behavior is consistent across different classes of yielding materials (e.g. microgels, glasses, associative polymers, filled polymer solutions), suggesting a universality of our observations. Beyond the explanation of the G’’ overshoot, the time-resolved nature of the experimental strain decomposition leads directly to a novel, fully-experimental paradigm for the understanding of large amplitude oscillatory shear (LAOS) data. This approach utilizes a novel time-resolved version of the Deborah number, which allows for the relative instantaneous viscoelasticity to be characterized, and for yielded and unyielded responses to be distinguished. We experimentally identify the specific sequence of physical processes that occurs in these materials during LAOS: 1) elastic deformation, 2) rapid, non-instantaneous yielding, and 3) plastic flow. We also show that this sequence of processes is nearly identical to that obtained from the analytical sequence of physical processes framework (SPP), which can therefore adequately capture the non-linear physics of yielding materials via simple measurements.