Paper Number
GG13 

Session
Rheology of Gels, Glasses and Jammed Systems

Title
No yield stress for yield-stress fluids

Presentation Date and Time
October 10, 2022 (Monday) 4:05

Track / Room
Track 3 / Sheraton 5

Authors (Click on name to view author profile)

  1. Pagani, Gabriele (ETH Zurich, ETH Zurich)
  2. Hofmann, Martin (ETH Zurich, Department of Materials)
  3. Govaert, Leon E. (Eindhoven University of Technology, Department of Mechanical Engineering)
  4. Tervoort, Theo A. (ETH Zurich, Department of Materials)
  5. Vermant, Jan (ETH Zürich, Materials)

Author and Affiliation Lines (in printed abstract book)
Gabriele Pagani1, Martin Hofmann1, Leon E. Govaert2, Theo A. Tervoort1 and Jan Vermant1
1Department of Materials, ETH Zurich, Zurich, ZH 8093, Switzerland; 2Department of Mechanical Engineering, Eindhoven University of Technology, Eindhoven, Brabant 5600 MB, The Netherlands

Speaker / Presenter 
Tervoort, Theo A.

Keywords
experimental methods; theoretical methods; colloids; emulsions; gels

Text of Abstract

This presentation is concerned with simple yield-stress fluids; nonthixotropic viscoplastic soft materials that exhibit solid-like behavior at low stress levels and switch to non-Newtonian fluid-like flow above a critical stress. The simplest description for these materials is arguably the Bingham model, which assumes rigid behavior below- and Newtonian fluid behavior above a constant yield stress. More complexity is given by the Herschel-Bulkley model providing non-Newtonian flow behavior above the yield stress.

The assumption of the existence of a true yield stress below which there is only elastic deformation (which is then often neglected), has met with criticism due to the emergence of a limiting zero-shear plateau value of the viscosity for a typical yield-stress fluid system such as Carbopol microgels of various concentrations [1].

The elasto-viscoplastic description of simple yield-stress fluids has received less attention [2] and is the topic of this presentation. Using creep curves measured at different stress levels for a Carbopol microgel, we will demonstrate the admissibility of time-stress superposition for this system. This is then used to construct a finite 3D constitutive equation that can describe nonlinear viscoelastic behavior including creep and the transition to Herschel-Bulkley-like flow without the need of a “yield stress”.

References:

1. Roberts, G. P. and Barnes, H. A., Rheol. Acta, 40, 499–503 (2001).

2. Dimitriou, C. J. and McKinley, G. H., J. Non-Newton. Fluid Mech., 265, 116–132 (2019).