Connection between fragility, mean-squared displacement and shear modulus in two van der Waals bonded glass-forming liquids

TL;DR

This study compares high-frequency shear modulus and nanosecond mean-squared displacement in two glass-forming liquids, testing and confirming the validity of two versions of the shoving model for their relaxation times.

Contribution

It provides experimental validation for the connection between shear modulus, mean-squared displacement, and relaxation times in van der Waals glass formers.

Findings

Both versions of the shoving model accurately describe the relaxation behavior.

The shear modulus and mean-squared displacement are experimentally correlated.

The models work well for cumene and 5PPE liquids.

Abstract

The temperature dependence of the high-frequency shear modulus measured in the kHz range is compared to the mean-squared displacement measured in the nanosecond range for the two van der Waals bonded glass-forming liquids cumene and 5PPE. This provides an experimental test for the assumption connecting two versions of the shoving model for the non-Arrhenius temperature dependence of the relaxation time in glass formers. The two versions of the model are also tested directly and both are shown to work well for these liquids.