Paper Number
PO21 

Session
Poster Session

Title
Shear banding in poloxamer wormlike micelles (WLMs) with slow dynamics

Presentation Date and Time
October 13, 2021 (Wednesday) 6:30

Track / Room
Poster Session / Ballroom 1-2-3-4

Authors (Click on name to view author profile)

  1. Huang, Christine (Carnegie Mellon University, Chemistry)
  2. McCauley, Patrick J. (University of Minnesota, Chemical Engineering and Materials Science)
  3. Calabrese, Michelle A. (University of Minnesota, Chemical Engineering and Materials Science)

Author and Affiliation Lines (in printed abstract book)
Christine Huang1, Patrick J. McCauley2 and Michelle A. Calabrese2
1Chemistry, Carnegie Mellon University, Pittsburgh, PA 15289; 2Chemical Engineering and Materials Science, University of Minnesota, Minneapolis, MN 55414

Speaker / Presenter 
Huang, Christine

Keywords
flow-induced instabilities; micelles; non-Newtonian fluids

Text of Abstract
Shear banding is a flow instability where, beyond a critical stress or shear rate, a homogeneous fluid flow separates into distinct regions or “bands” of viscosity and underlying structure. Although shear banding has received considerable attention, the mechanism of shear band formation is unclear. Suggested mechanisms in literature include nucleation and growth and disentangle-re-entanglement, but the criteria for selecting one mechanism over another for a given material and flow are unknown. We explore these mechanisms by studying the shear banding evolution of wormlike micelles (WLMs), the archetypical system for these instabilities, across a variety of flow conditions. Here, long, entangled micelles are composed of triblock poloxamers with polyethylene oxide (PEO) end blocks and polypropylene oxide (PPO) midblock, which rearrange and break on slow timescales (t~3000 seconds). As shear bands are localized structures that vary in both space and time, we use a combination of time-dependent nonlinear rheology and spatiotemporal flow small angle neutron scattering (flowSANS) to characterize shear band formation and evolution. The slow dynamics of this system increase the temporal resolution of shear band development relative to the relaxation time, providing new insights on the microstructural evolution of both transient and steady state shear bands. The mechanism of shear band formation in these systems is a function of applied shear rate, where transient shear banding appears to follow the nucleation and growth mechanism, while steady state shear banding follows the disentangle-re-entanglement mechanism. These differences in mechanism help to distinguish transient and steady state shear banding.