On the mechanism of the highly viscous flow

TL;DR

This paper presents an improved asymmetry model explaining highly viscous flow through thermally activated structural jumps and their relaxation, aligning well with experimental data and linking viscosity to shear compliance and Maxwell time.

Contribution

The paper introduces an enhanced asymmetry model that quantitatively describes viscous flow in glassy materials using shear compliance and relaxation spectra.

Findings

Model aligns with experimental viscosity measurements.

Viscosity linked to the cutoff of retardation spectrum.

Cutoff near the Maxwell time for consistency.

Abstract

The asymmetry model for the highly viscous flow postulates thermally activated jumps from a practically undistorted ground state to strongly distorted, but stable structures, with a pronounced Eshelby backstress from the distorted surroundings. The viscosity is ascribed to those stable distorted structures which do not jump back, but relax by the relaxation of the surrounding viscoelastic matrix. It is shown that this mechanism implies a description in terms of the shear compliance, with a viscosity which can be calculated from the cutoff of the retardation spectrum. Consistency requires that this cutoff lies close to the Maxwell time. The improved asymmetry model compares well with experiment.