Paper Number
SF7 

Session
Surfactants, Foams, and Emulsions

Title
Recovery rheology via rheo-SANS: Application to step strains under out-of-equilibrium conditions

Presentation Date and Time
October 21, 2019 (Monday) 1:55

Track / Room
Track 5 / Room 306A

Authors (Click on name to view author profile)

  1. Lee, Johnny Ching-Wei (University of Illinois at Urbana-Champaign, Chemical and Biomolecular Engineering)
  2. Porcar, Lionel (Institut Laue-Langevin)
  3. Rogers, Simon A. (University of Illinois at Urbana-Champaign, Department of Chemical and Biomolecular Engineering)

Author and Affiliation Lines (in printed abstract book)
Johnny Ching-Wei Lee1, Lionel Porcar2, and Simon A. Rogers1
1Chemical and Biomolecular Engineering, University of Illinois at Urbana-Champaign, Urbana, IL 61801; 2Institut Laue-Langevin, Grenoble, France

Speaker / Presenter 
Lee, Johnny Ching-Wei

Text of Abstract
Stress relaxation from a step strain test provides important information about constituent dynamics, but if a material has experienced a complex shear history, the underlying physics is not straightforward to access. We use recovery rheology and rheo-small-angle neutron scattering (rheo-SANS) to probe the nonlinear dynamics of an entangled wormlike micelle solution by applying step strains after complex shear histories enforced by large-amplitude oscillatory shear (LAOS) flow. We show that a universal relaxation modulus can be obtained from step strain tests with complex shear histories, as long as the modulus is defined in term of the recoverable strain. The shear and normal stresses, as well as the alignment of micellar Kuhn segments, are shown to be positively correlated with the recoverable strain. We identify re-entanglement of polymeric chains after cessation of LAOS and show that this process occurs over the same timescales as linear-regime stress relaxation. This work therefore lays the foundation of how to accurately probe out-of-equilibrium rheology in a consistent manner.