Paper Number
PG9
Session
Polyelectrolytes, Self-assembling Systems & Gels
Title
A direct correlation between the evolution of microstructure and recoverable strain in wormlike micellar solutions
Presentation Date and Time
October 17, 2018 (Wednesday) 9:50
Track / Room
Track 3 / Bellaire
Authors
- Lee, Ching-Wei (University of Illinois at Urbana-Champaign, Chemical and Biomolecular Engineering)
- Rogers, Simon A. (University of Illinois at Urbana-Champaign, Chemical and Biomolecular Engineering)
Author and Affiliation Lines
Ching-Wei Lee and Simon A. Rogers
Chemical and Biomolecular Engineering, University of Illinois at Urbana-Champaign, Urbana, IL 61801
Speaker / Presenter
Lee, Ching-Wei
Text of Abstract
Combining in-situ time-resolved small angle neutron scattering (SANS) and dynamic shear rheology, we demonstrate that the evolution of micellar segmental alignment is well correlated with the recoverable strain. The shear-induced alignments in both velocity-gradient and velocity-vorticity planes are shown to be dictated by the recoverable strain, independent of the imposed frequency. The micellar system exhibits a distinct sequence of physical processes under large amplitude oscillatory shear (LAOS) that begins at small recoverable strains with an interval of linear viscoelasticity, before transitioning to an interval of softening/thinning as the recoverable strain increases, and then recoiling as the recoverable strain decreases. This clearly identifiable sequence takes place twice per oscillation. While LAOS responses are typically viewed as being somehow intermediate cases, we demonstrate that information regarding both axes of Pipkin space, which consist of the steady-state flow curve and the linear-regime frequency sweep, can be obtained within the response to LAOS.
In addition to a clear interpretation of the shear stress response, we also investigate the normal stress response as a function of the transient recoverable strain. The first normal stress difference shows an open butterfly shape when plotted against the total strain, but shows a simple closed parabola when plotted against the recoverable strain. We observe minimum normal stress at zero recoverable strain and a normal stress that increases quadratically with the recoverable strain. This work provides a physical and straightforward path to further explore the rheological and microstructural evolutions of self-assembled and polymeric materials under flow.