Paper Number
GG15 

Session
Rheology of Gels, Glasses and Jammed Systems

Title
On the nature of the flow curves of thixotropic materials

Presentation Date and Time
October 10, 2022 (Monday) 4:45

Track / Room
Track 3 / Sheraton 5

Authors (Click on name to view author profile)

  1. Bhattacharyya, Tulika (Indian Institute of Technology Kanpur, Department of Chemical Engineering)
  2. Jacob, Alan R. (Indian Institute of Technology Hyderabad, Department of Chemical Engineering)
  3. Petekidis, George (IESL-FORTH)
  4. Joshi, Yogesh M. (Indian Institute of Technology, Chemical Engineering)

Author and Affiliation Lines (in printed abstract book)
Tulika Bhattacharyya1, Alan R. Jacob2, George Petekidis3 and Yogesh M. Joshi1
1Department of Chemical Engineering, Indian Institute of Technology Kanpur, Kanpur, UP 208016, India; 2Department of Chemical Engineering, Indian Institute of Technology Hyderabad, Hyderabad, Telangana 502284, India; 3IESL-FORTH, Heraklion, Greece

Speaker / Presenter 
Joshi, Yogesh M.

Keywords
experimental methods; theoretical methods; colloids; gels; glasses; jammed systems; suspensions

Text of Abstract
Thixotropy concerns a decrease in viscosity as a function of time under application of a sufficiently strong flow field and recovery of the same when the flow field is removed. In this work, we study the nature of steady-state flow curves (shear stress – shear rate relationship) of three different materials: suspensions of spherical particles with hard-sphere interactions (volume fractions 0.625 and 0.595.), aqueous Laponite dispersions (age since preparation 14 and 1000 days) and Carbopol dispersion. We also study two kinds of structural kinetic models: inelastic thixotropic and viscoelastic thixotropic. Analysis of experimental as well as theoretical results suggests that thixotropic materials show constant as well as time-dependent yield stress. Furthermore, when thixotropic material shows time-dependent yield stress, analysis of the same through thixotropic models indicates presence of non-monotonic flow curves, which otherwise is difficult to guess from conventional rheological experiments. Consequently, this work suggests that merely by looking at the steady state flow curve one cannot rule out the presence of thixotropy in a material. In addition, we observe that dependence of relaxation time on time shows a power law relationship in such a fashion that the power law exponent decreases with increase in stress. In a limit of stress approaching the yield stress, the power law coefficient is observed to tend to zero that is suggestive of yielding transition.