On the breakdown of the simple Arrhenius law in the normal liquid state

TL;DR

This paper demonstrates that the Arrhenius law fails to accurately describe the temperature dependence of molecular dynamics in glass formers like propylene carbonate, especially at elevated pressures, and proposes a modified model for better description.

Contribution

It provides experimental evidence against the simple Arrhenius law in the normal liquid state and introduces a modified MYEGA model for improved dynamics description.

Findings

Arrhenius law does not hold at elevated pressures

Thermodynamic density scaling reveals inflection points in data

Modified MYEGA model better fits the observed dynamics

Abstract

It is common practice to discuss the temperature effect on molecular dynamics of glass formers above the melting temperature in terms of the Arrhenius law. Using dielectric spectroscopy measurements of dc-conductivity and structural relaxation time on the example of the typical glass former propylene carbonate, we provide experimental evidence that this practice is not justified. Our conclusions are supported by employing thermodynamic density scaling and the occurrence of inflection points in isothermal dynamic data measured at elevated pressure. Additionally, we propose a more suitable approach to describe the dynamics both above and below the inflection point based upon a modified MYEGA model.