Paper Number
SG9 

Session
Self-assembled Systems, Gels and Liquid Crystals

Title
Reinterpreting viscoelasticity in terms of Laun’s elastic strain and an equilibrium shift: Application to worm-like micelles

Presentation Date and Time
February 13, 2017 (Monday) 2:45

Track / Room
Track 3 / White Ibis

Authors (Click on name to view author profile)

1. Lee, Ching-Wei (University of Illinois at Urbana-Champaign, Chemical and Biomolecular Engineering)
2. Park, Jun Dong (University of Illinois at Urbana-Champaign, Department of Chemical & Biomolecular Engineering)
3. Rogers, Simon A. (University of Illinois, Urbana Champaign, Chemical & Biomolecular Engineering)

Author and Affiliation Lines (in printed abstract book)
Ching-Wei Lee, Jun Dong Park, and Simon A. Rogers
Chemical & Biomolecular Engineering, University of Illinois, Urbana Champaign, Urbana, IL

Speaker / Presenter 
Rogers, Simon A.

Text of Abstract
The strain- and stress-controlled viscoelastic response of a linear worm-like micellar is interpreted in terms of Laun’s elastic strain [Laun, J. Rheol. 30, 459 (1986)] and a moving equilibrium position. Within this framework, the modulus and viscosity are shown to be constant in the linear regime, and all dynamics are accounted for by the moving equilibrium position. Notably, we measure a constant modulus (the plateau modulus) by mapping the elastic strain, and a constant viscosity (the zero-shear viscosity) by following the transience of the equilibrium position. Even in small-amplitude oscillatory shearing (SAOS), these measurements are independent of frequency over a wide range of frequencies. Having identified and measured the elastic strain, modulus, and viscosity, we are able to calculate the instantaneous energy stored and dissipated, and show that the averages of our measured values scale with the dynamic moduli. We show that the micellar rheology can be described by a single equation that accounts for responses to step strains, step rates, step stresses, and oscillatory stresses and strains. The successful explanation of the micellar rheology suggests that a coupling of Laun’s elastic strain concept and a moving equilibrium has significant utility in understanding other nonlinear protocols, notably large amplitude oscillatory shear (LAOS).