Structural relaxation and highly viscous flow

TL;DR

This paper explains the microscopic mechanisms behind highly viscous flow in undercooled liquids, emphasizing thermally activated structural transitions and their impact on viscosity and relaxation times.

Contribution

It provides a self-consistent model linking Eshelby transitions to viscosity, clarifying why relaxation times exceed Maxwell times by a factor of eight.

Findings

Average structural relaxation time is eight times longer than Maxwell time.

Large contribution of strained inherent states to fluidity.

Viscous no-return processes coexist with retardation processes at Maxwell time.

Abstract

The highly viscous flow is due to thermally activated Eshelby transitions which transform a region of the undercooled liquid to a different structure with a different elastic misfit to the viscoelastic surroundings. A self-consistent determination of the viscosity in this picture explains why the average structural relaxation time is a factor of eight longer than the Maxwell time. The physical reason for the short Maxwell time is the very large contribution of strongly strained inherent states to the fluidity (the inverse viscosity). At the Maxwell time, the viscous no-return processes coexist with the back-and-forth jumping retardation processes.