Paper Number
SM43 

Session
Polymers Solutions, Melts and Blends

Title
The first-ever medium-amplitude oscillatory shear stress (MAOStress) measurement

Presentation Date and Time
October 12, 2022 (Wednesday) 2:10

Track / Room
Track 2 / Sheraton 3

Authors (Click on name to view author profile)

  1. Ramlawi, Nabil (University of Illinois Urbana Champaign, Mechanical Science and Engineering)
  2. Hossain, Mohammad Tanver (University of Illinois at Urbana-Champaign, Department of Mechanical Science and Engineering)
  3. Shetty, Abhishek (Anton Paar USA Inc., Rheology Department, Advanced Technical Center)
  4. Ewoldt, Randy H. (University of Illinois at Urbana-Champaign, Mechanical Science and Engineering)

Author and Affiliation Lines (in printed abstract book)
Nabil Ramlawi1, Mohammad Tanver Hossain1, Abhishek Shetty2 and Randy H. Ewoldt1
1Mechanical Science and Engineering, University of Illinois at Urbana-Champaign, Urbana, IL 61801; 2Rheology Department, Advanced Technical Center, Anton Paar USA Inc., Ashland, VA 23005

Speaker / Presenter 
Ramlawi, Nabil

Keywords
experimental methods; polymer solutions; rheometry techniques

Text of Abstract
We report the first-ever complete measurement of MAOStress material functions, using PVA-Borax, a transiently crosslinked polymer network, and a stress-controlled rheometer having an electronically commutated (EC) motor. Moreover, we outline experimental limit lines and their dependence on geometry and test conditions. These MAOStress measurements enable us to observe the frequency dependence of the weakly nonlinear deviation as a function of stress-amplitude. The observed features of MAOStress material functions are distinctly simpler compared to MAOStrain where the dependence on frequency is much more dramatic. For comparison, we simulate the single-mode SSTNM model [1], which showed a constant intrinsic nonlinearity as a function of frequency. Although the SSTNM model can capture features of MAOStrain material functions [1], the absence of a retardation timescale makes it inadequate to capture the frequency dependence present in MAOStress. Moreover, we compare the limits of the MAOStress and MAOStrain regimes to understand the ease of sampling of the weakly nonlinear regime at different frequencies. Notably, the critical stress amplitude to observe the weakly nonlinear regime has an opposite trend as a function of De compared to the critical strain from MAOStrain. This work extends the experimental accessibility of the weakly nonlinear regime to stress-controlled instruments and deformations, which reveal material physics beyond linear viscoelasticity but at conditions that are accessible to theory and detailed simulation[2]. [1] N. A. Bharadwaj, K. S. Schweizer, and R. H. Ewoldt, “A strain stiffening theory for transient polymer networks under asymptotically nonlinear oscillatory shear,” J. Rheol., vol. 61, no. 4, pp. 643–665, 2017. [2] R. H. Ewoldt and N. A. Bharadwaj, “Low-dimensional intrinsic material functions for nonlinear viscoelasticity,” Rheol. Acta, vol. 52, no. 3, pp. 201–219, 2013.