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Terminal stage of highly viscous flow
1Forschungszentrum Jülich GmbH, Jülich Centre for Neutron Science (JCNS-1) and Institute for Complex Systems (ICS-1), 52425 Jülich, Germany.
Physical Review. E
|September 16, 2022
Summary
This study introduces a shear misfit model for viscous flow, predicting a Debye peak in dielectric spectra. The model explains faster thermal expansion equilibration in polymers by accounting for adiabatic density fluctuations.
Area of Science:
- Rheology and viscoelasticity
- Glass transition physics
- Dielectric spectroscopy
Background:
- Highly viscous flow exhibits complex relaxation behaviors.
- The terminal stage of viscous flow is theoretically challenging.
- Experimental evidence suggests a Debye peak in dielectric spectra.
Purpose of the Study:
- To present a shear misfit model for highly viscous flow.
- To explain the terminal stage using irreversible Eshelby relaxations.
- To investigate density fluctuations and compressibility at the glass transition.
Main Methods:
- Theoretical modeling based on five-dimensional shear space.
- Analysis of dielectric, shear, and bulk relaxation data.
- Application to vacuum pump oils and squalane.
Main Results:
- The model predicts a Debye peak in dielectric spectra, aligning with experimental data.
- A relationship between adiabatic and isothermal compressibility jumps at the glass transition is derived.
- Adiabatic density fluctuations explain faster thermal expansion equilibration in squalane.
Conclusions:
- The shear misfit model provides a framework for understanding viscous flow and relaxation phenomena.
- The model successfully explains experimental observations, including dielectric spectra and thermal expansion dynamics.
- This work offers insights into the interplay between density fluctuations and thermal properties near the glass transition.
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