Paper Number
PO17
Session
Poster Session
Title
Insights from recovery rheology applied to step-strain and start-up of shear flows
Presentation Date and Time
October 23, 2019 (Wednesday) 6:30
Track / Room
Poster Session / Ballroom C on 4th floor
Authors
- Singh, Piyush K. (University of Illinois at Urbana-Champaign, Department of Chemical And Biomolecular Engineering)
- Lee, Johnny Ching-Wei (University of Illinois at Urbana-Champaign, Chemical and Biomolecular Engineering)
- Rogers, Simon A. (University of Illinois at Urbana-Champaign, Department of Chemical and Biomolecular Engineering)
Author and Affiliation Lines
Piyush K. Singh, Johnny Ching-Wei Lee, and Simon A. Rogers
Department of Chemical and Biomolecular Engineering, University of Illinois at Urbana-Champaign, Urbana, IL 61801
Speaker / Presenter
Singh, Piyush K.
Text of Abstract
Material functions are at the core of every rheological study. It is through the presentation of material functions that we describe the physics that dictate the behavior of soft materials. Traditional rheological metrics such as moduli and viscosities are defined in the official nomenclature of the Society of Rheology in terms of the total strain and the rate at which the total strain changes, respectively. Recent works have shown significant benefit in distinguishing between the total strain and the recoverable strain, even in strain-controlled tests [Lee et al, Phys. Rev. Lett. (2019); Lee et al, AICHE J (2019)]. It has been shown that elastic moduli that are defined in terms of the recoverable strain and viscosities that are defined in terms of the rate of acquisition of unrecoverable strain can be clearly correlated across a range of linear and transient nonlinear rheological tests. In this work, investigating a well-studied system of wormlike micelles, we further apply the ideas of recovery rheology to two of the most common experiments in rheometry, step strain and start up of shear. We show that quantities defined in terms of recoverable and unrecoverable strains, especially for these transient flows, are remarkably consistent across distinct flow types. Furthermore, such quantities yield the same information across test conditions. For example, despite the micellar solution being known to be shear-thinning under steady-state flow, we show that at early times under a wide range of nonlinear shear rates that the same (zero-shear) viscosity is observed. Our results have strong implications for fundamental questions such as how we define moduli and viscosities under transient flow conditions, as well as how we define useful dimensionless groups such as transient Deborah and Weissenberg numbers.