Paper Number
PO5
Session
Poster Session
Title
The role of elasticity in thixotropy: Elastic stress during parallel superposition
Presentation Date and Time
October 23, 2019 (Wednesday) 6:30
Track / Room
Poster Session / Ballroom C on 4th floor
Authors
- Choi, Jiho (University of Illinois at Urbana-Champaign, Department of Chemical and Biomolecular Engineering)
- Rogers, Simon A. (University of Illinois at Urbana-Champaign, Department of Chemical and Biomolecular Engineering)
Author and Affiliation Lines
Jiho Choi and Simon A. Rogers
Department of Chemical and Biomolecular Engineering, University of Illinois at Urbana-Champaign, Urbana, IL 61801
Speaker / Presenter
Choi, Jiho
Text of Abstract
Materials that display thixotropy, or time-dependent viscosities, are ubiquitous in industry, the environment, and consumer products. Despite the wide-spread use and importance of thixotropic materials, theoretical descriptions still fail to accurately describe the complex behaviors exhibited in transient flows. Here, we employ a series of complex transient tests to experimentally probe those complex dynamics. We use flow cessation tests [1] to identify transient elastic stresses during stress jump tests which are commonly used to identify 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. This laborious experimental method of obtaining elastic stress is compared to calculations of the elastic stress from a rapid and novel analysis of parallel superposition tests based on the sequence of physical processes (SPP) [2] framework. In the SPP framework, the elastic stress is calculated via integration of the SPP modulus, which echoes the importance of elasticity in thixotropy, in that it also follows the shape of total stress in parallel superposition. Therefore, we can obtain the elastic stress using the SPP framework significantly quicker than by a series of flow cessation tests. While parallel superposition tests have previously been analyzed by dividing the stress into steady and oscillating components, the SPP framework treats all stress equally, and enables us to obtain accurate viscoelastic metrics for parallel superposition. These results show that we can extend the utility of the SPP approach to the study of thixotropy and parallel superposition, which has so far been limited to large amplitude oscillatory shear studies only.[1] Dullaert, K., and J. Mewis, “Stress jumps on weakly flocculated dispersions,” J. Colloid Interface Sci. 287, 542-551 (2005).[2] Rogers. S. A., “In search of physical meaning,” Rheol. Acta. 56, 501-525 (2017).