Paper Number
PO74 

Session
Poster Session

Title
Elastic stress during stepwise reduction in shear rate for thixotropic suspension

Presentation Date and Time
October 17, 2018 (Wednesday) 6:30

Track / Room
Poster Session / Woodway II/III

Authors (Click on name to view author profile)

1. Choi, Jiho (University of Illinois at Urbana-Champaign, Chemical and Biomolecular Engineering)
2. Rogers, Simon A. (University of Illinois at Urbana-Champaign, Chemical and Biomolecular Engineering)

Author and Affiliation Lines (in printed abstract book)
Jiho Choi and Simon A. Rogers
Chemical and Biomolecular Engineering, University of Illinois at Urbana-Champaign, Urbana, IL 61801

Speaker / Presenter 
Choi, Jiho

Text of Abstract
A comprehensive series of time-resolved stress jump tests is performed on a thixotropic fumed silica suspension to determine elastic contributions to thixotropic behaviors. The series of stress jumps tests is the most complete performed to date, encompassing jumps between three well-defined flow states, as well as flow reversals. We employ an experimental technique for measuring the elastic stress [1] in which flow is abruptly stopped. The elastic stress is identified via an extrapolation back to the moment of flow cessation. The elastic stress is measured across a range of shear rates, and during the transient response to a jump from one rate to another, providing a detailed data set that shows the importance of elasticity in thixotropy. It is shown that the evolution of the elastic stress closely follows that of total stress in the series of stress jump tests, indicating that elasticity is a significant contributor to thixotropy. The elastic stress is also calculated via the integration of a sequence of physical processes (SPP) [2] metric obtained from parallel superposition tests. The elastic stress calculated by integration of the SPP metrics matches the values measured via the stress jumps, but is obtained in a small fraction of the time required for full experimental discovery. These results highlight the utility of the SPP approach, which has so far been limited to LAOS studies only, in the study of thixotropy, and also indicate the importance of elasticity in thixotropy. [1] Dullaert, K., and J. Mewis, “Stress jumps on weakly flocculated dispersions: Steady state and transient results,” J. Colloid and Interface Science. 287, 542-551 (2005). [2] Rogers. S. A., “In search of physical meaning: defining transient parameters for nonlinear viscoelasticity,” Rheol. Acta. 56, 501-525 (2017).