High resolution shear profile measurements in entangled polymers.
Keesha A Hayes1, Mark R Buckley, Itai Cohen
1School of Chemical & Biomolecular Engineering, Cornell University, Ithaca, New York 14853, USA.
Physical Review Letters
|December 31, 2008
Summary
Entangled polymer solutions exhibit linear velocity profiles, challenging shear banding theories. Interfacial slip, not shear banding, likely causes strain loss in these polymer flows.
Area of Science:
- Polymer Physics
- Rheology
- Fluid Dynamics
Background:
- Entangled polymers exhibit complex flow behaviors under shear.
- Recent studies suggest shear banding is a universal response in these systems.
- Understanding polymer flow is crucial for material science and engineering.
Purpose of the Study:
- To investigate the flow dynamics of entangled polymers under rectilinear shear.
- To determine the validity of shear banding as a characteristic flow response.
- To identify the primary mechanisms responsible for strain loss.
Main Methods:
- Utilized confocal microscopy to track fluorescent tracer particles (250-300 nm).
- Employed particle image velocimetry to quantify fluid motion.
- Applied rectilinear shear flow to polymer solutions with varying entanglement levels (Z=8-56).
Main Results:
- Observed linear velocity profiles across all tested polymer solutions.
- Detected significant discrepancies between imposed and measured shear rates.
- Found no evidence supporting shear banding as the dominant flow mechanism.
Conclusions:
- Linear velocity profiles are consistent in entangled polymers, irrespective of molecular weight or entanglement density.
- Interfacial slip is identified as a key factor contributing to strain loss.
- Results challenge the prevailing view of shear banding as a universal response in entangled polymer flow.
