Paper Number
PO20 

Session
Poster Session

Title
Shear banding and wall slip in polymer wormlike micelles

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. McCauley, Patrick J. (University of Minnesota, Chemical Engineering and Materials Science)
2. Pham, Lucas H. (University of Minnesota, Chemical Engineering and Materials Science)
3. Kumar, Satish (University of Minnesota, Chemical Engineering and Materials Science)
4. Calabrese, Michelle A. (University of Minnesota, Chemical Engineering and Materials Science)

Author and Affiliation Lines (in printed abstract book)
Patrick J. McCauley, Lucas H. Pham, Satish Kumar and Michelle A. Calabrese
Chemical Engineering and Materials Science, University of Minnesota, Minneapolis, MN 55414

Speaker / Presenter 
McCauley, Patrick J.

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

Text of Abstract
Shear banding, the separation of flow into distinct regions of structure and viscosity, is well- studied in wormlike micelles (WLMs) and often accompanied by some degree of wall slip, a phenomenon where the velocity of a fluid at moving surface is less than the solid boundary. Despite their frequent association, the role of wall slip in shear banding instabilities is still not fully understood. Some work suggests wall slip is only present at early times in the evolution of the shear bands whereas other work has shown prolonged wall slip. To better understand the relationship between these phenomena, we use a model system of WLMs exhibiting slow dynamics, formed from triblock poloxamers with polyethylene oxide (PEO) end blocks and polypropylene oxide (PPO) midblocks. Previous work on poloxamer WLMs established the clear presence of wall slip across a range of shear rates. As shear rate increases, the flow transitions from a region with only wall slip to both shear banding and wall slip, but the criteria governing this transition is unclear. Here, the interplay between shear banding and wall slip is studied via a combination of rheology and particle tracking velocimetry. Concentric cylinder geometries with varying inner cylinder radii and surface finishes are used to access conditions with varying wall slip. Additionally, using prior knowledge of the variation of poloxamer WLM structure and properties with temperature, material relaxation time is tuned, probing the impact of the WLM relaxation time on wall slip and banding as well. The interplay of wall slip and shear banding across the range of geometries and relaxation times examined here provides new insights on the role of wall slip on shear banding instabilities.