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Edge-Induced Shear Banding in Entangled Polymeric Fluids
Ewan J Hemingway1, Suzanne M Fielding1
1Department of Physics, Durham University, Science Laboratories, South Road, Durham DH1 3LE, United Kingdom.
Physical Review Letters
|April 26, 2018
Summary
Edge disturbances in polymer melts can induce shear banding, even when the material's intrinsic properties suggest otherwise. These secondary flows, driven by subtle surface irregularities, can significantly impact bulk fluid behavior.
Area of Science:
- Polymer physics
- Rheology
- Fluid dynamics
Background:
- Shear banding in entangled polymers is a controversial phenomenon.
- The existence of a negative slope in the shear stress vs. shear rate (dσ/dγ̇ < 0) is theoretically linked to shear banding.
- Experimental studies are often limited by edge fracture, an instability at the fluid-air interface.
Purpose of the Study:
- To investigate the role of edge disturbances in inducing shear banding in polymer melts.
- To determine if shear banding can occur even with a monotonically increasing constitutive curve.
- To understand the influence of subtle edge effects on bulk flow behavior.
Main Methods:
- Numerical simulations of polymer flow under shear.
- Modeling of modest edge disturbances and their impact on flow fields.
- Analysis of secondary flows and shear band formation.
Main Results:
- Even minor edge disturbances can initiate strong secondary flows resembling shear bands.
- These simulated shear bands penetrate deeply into the fluid bulk.
- Shear banding was observed even when the underlying constitutive curve was monotonically increasing, contradicting bulk banding theories.
Conclusions:
- Edge effects, not just intrinsic material properties, can drive shear banding in polymer melts.
- Subtle, potentially unnoticed, edge disturbances can lead to significant bulk flow modifications.
- The study highlights the importance of considering boundary conditions in understanding polymer rheology.
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