Paper Number
GG16
Session
Rheology of Gels, Glasses and Jammed Systems
Title
Thixotropic constitutive modeling of shear banding by boundary-induced modulus gradient in lamellar gel networks
Presentation Date and Time
October 10, 2022 (Monday) 5:05
Track / Room
Track 3 / Sheraton 5
Authors
- Wang, Futianyi (University of Michigan, Department of Chemical Engineering)
- Larson, Ronald (University of Michigan-Ann Arbor, Chemical Engineering Department)
Author and Affiliation Lines
Futianyi Wang and Ronald Larson
Chemical Engineering Department, University of Michigan-Ann Arbor, Ann Arbor, MI 48105
Speaker / Presenter
Wang, Futianyi
Keywords
consumer products; emulsions; gels; surfactants
Text of Abstract
To predict the complex rheology and shear-rate inhomogeneities of lamellar gel networks, we propose a simple thixotropic constitutive model with an elasto-plastic stress and a smoothly decreasing modulus near a solid boundary. We show that the model qualitatively captures the important features of the lamellar gel shear rheology observed in experiments. These include thixotropic shear-thinning that is intermediate between constant viscosity and constant stress, a power-law slow creep under small constant shear stress and abrupt transition to fast creep at higher stress, as well as partial recovery of strain upon stress removal. In addition, the model correctly predicts a gap-dependent rheology, and roughly predicts the frequency dependence of storage and loss moduli in oscillatory tests. Most importantly, the introduction of the modulus gradient enables the model to predict the unique shear banding phenomenon of lamellar gel networks wherein a thin, fast-shearing band exists near the boundary that widens only slowly with increased apparent shear rate until a high rate is reached, while the bulk moves as a plug. We discuss the influence of a lower modulus near the boundary and its possible origin in the underlying lamellar structure of the material.