Paper Number
PO58 

Session
Poster Session

Title
Understanding steady and dynamic shear banding in a model wormlike micellar solution

Presentation Date and Time
February 15, 2017 (Wednesday) 6:00

Track / Room
Poster Session / Foyer-Stairs/Windows

Authors (Click on name to view author profile)

1. Calabrese, Michelle A. (University of Delaware, Chemical & Biomolecular Engineering)
2. Rogers, Simon A. (University of Illinois, Urbana Champaign, Chemical & Biomolecular Engineering)
3. Porcar, Lionel (Institut Laue-Langevin, Large Scale Structures)
4. Wagner, Norman J. (University of Delaware, Chemical & Biomolecular Engineering)

Author and Affiliation Lines (in printed abstract book)
Michelle A. Calabrese¹, Simon A. Rogers², Lionel Porcar³, and Norman J. Wagner^1
1Chemical & Biomolecular Engineering, University of Delaware, Newark, DE 19716; ²Chemical & Biomolecular Engineering, University of Illinois, Urbana Champaign, Urbana, IL; ³Large Scale Structures, Institut Laue-Langevin, Grenoble, France

Speaker / Presenter 
Calabrese, Michelle A.

Text of Abstract
Shear banding under steady and dynamic deformation is examined in a model wormlike micellar solution to experimentally validate predictions of the Vasquez-Cook-McKinley (VCM) model, which explicitly accounts for breakage and reformation events leading to shear banding (Zhou, et al., JNNFM 2010). Shear banding is confirmed using a combination of rheology and flow-small angle neutron scattering (flow-SANS) measurements, where startup rheology and flow-SANS reveal long transients during shear band formation (Calabrese, et al., JOR 2016). Spatially- and temporally-resolved flow-SANS measurements probe the microstructure during steady and dynamic shear banding. Under large amplitude oscillatory shear (LAOS) deformation, shear banding is dependent on the Deborah and Weissenberg numbers, validating the VCM model predictions. Micelle segmental alignment in the flow-gradient plane during LAOS is a complex function of cycle time, radial position, frequency and shear rate. The maximum segmental alignment under LAOS often exceeds that of the corresponding shear rate under steady shear, termed “over-orientation.” Guidelines for LAOS shear banding are developed based on LAOS rheological features and degree of over-orientation. The results of this study present new methods for identifying shear banding under steady and dynamic deformation, while providing an extensive data set for the development and further improvement of constitutive models.