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Nematic effects and strain coupling in entangled polymer melts under strong flow
Jacob J K Kirkensgaard1, Ludovica Hengeller2, Andriy Dorokhin3
1Niels Bohr Institute, University of Copenhagen, Universitetsparken 5, 2100 Copenhagen, Denmark.
Physical Review. E
|September 15, 2016
Summary
Small-angle neutron scattering reveals nematic effects in polymer blends. Short chains stretch 1.5x more in a long chain nematic field, impacting polymer dynamics and relaxation.
Area of Science:
- Polymer Physics
- Materials Science
- Rheology
Background:
- Understanding polymer chain dynamics is crucial for material properties.
- Entangled polymer melts exhibit complex flow behaviors.
- Nematic ordering can influence chain stretching and relaxation.
Purpose of the Study:
- To investigate the impact of a long-chain nematic field on short chain stretching.
- To analyze strain coupling in pure melts versus nematic systems.
- To elucidate nonlinear relaxation mechanisms in polymer blends.
Main Methods:
- Small-angle neutron scattering (SANS) on labeled short polymer chains.
- Studying blends with and without entangled, stretched long chains.
- Analysis of polymer chain conformation and relaxation dynamics.
Main Results:
- Unequivocal evidence of nematic effects enhancing short chain stretching by ~1.5x.
- Confirmation of nonaffine mean-field result (ν=0.5) for fast flows in pure melts.
- Prediction of increased coupling constant in nematic systems.
- Structural explanation for nonlinear relaxation regimes, including a transition phase.
Conclusions:
- Nematic fields significantly influence polymer chain conformation and stretching.
- Polymer blend dynamics differ substantially from pure melts under flow.
- The study provides insights into the complex relaxation processes in entangled polymer systems.
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