Journal
JOURNAL OF NON-NEWTONIAN FLUID MECHANICS
Volume 208, Issue -, Pages 27-41Publisher
ELSEVIER
DOI: 10.1016/j.jnnfm.2014.03.006
Keywords
Thixotropy; Viscoelasticity; Large amplitude oscillatory shear; Asymptotic nonlinearities
Categories
Ask authors/readers for more resources
Here we demonstrate that a simple thixotropic constitutive model produces unique signatures in large-amplitude oscillatory shear (LAOS) distinct from other nonlinear mechanisms and separate from viscoelastic time dependence. Our approach is to define the simplest model that produces the essential features of both thixotropy and viscoelasticity, a structure-parameter evolution equation coupled to a three-element fluid (Jeffreys model). In strain-controlled LAOS, the response of the model depends on four dimensionless parameters: two deformation parameters (Deborah and Weissenberg) and two material parameters (the ratio of viscoelastic to thixotropic timescales and the ratio of infinite shear viscosity to aggregate viscosity). We present numerical results for the full nonlinearities across this four-dimensional parameter space. The dimensionality is reduced by considering the asymptotically-nonlinear regime (Weissenberg number expansion). We present the first analytical solution for a thixotropic model in this asymptotically-nonlinear LAOS regime, which produces distinct power function scaling not predicted by other known solutions to nonlinear viscoelastic models. With this separation of thixotropic from viscoelastic timescales, this canonical model predicts that short thixotropic timescales can be experimentally observed with nonlinear oscillatory deformation. This is relevant to recent suggestions in distinguishing thixotropic versus simple yield stress fluids with no experimentally observable thixotropy. (C) 2014 Elsevier B.V. All rights reserved.
Authors
I am an author on this paper
Click your name to claim this paper and add it to your profile.
Reviews
Recommended
No Data Available