MD Simulations of Charged Binary Mixtures Reveal a Generic Relation Between High- and Low-Temperature Behavior

TL;DR

This study uses molecular dynamics simulations of charged binary mixtures to reveal a universal quadratic relation between high-temperature activation energy and glass transition temperature, linking high- and low-temperature dynamics in glass-forming liquids.

Contribution

It introduces a phenomenological model and demonstrates a robust quadratic relation between activation energy and glass transition temperature across different conditions.

Findings

Quadratic charge dependence of $E_{ ext{infty}}$ and $T_g$

Constant ratio of $E_{ ext{infty}}$ to $T_g$ independent of conditions

High-temperature activation energy can predict $T_g$

Abstract

Experimental studies of the glassy slowdown in molecular liquids indicate that the high-temperature activation energy $E_{\infty}$ of glass-forming liquids is directly related to their glass transition temperature $T_{\text{g}}$. To further investigate such a possible relation between high- and low-temperature dynamics in glass-forming liquids, we analyze the glassy dynamics of binary mixtures using molecular dynamics (MD) simulations. We consider a binary mixture of charged Lennard-Jones particles and vary the partial charges of the particles, and thus, the high-temperature activation energy and the glass transition temperature of the system. Based on previous results, we introduce a phenomenological model describing relaxation times over the whole temperature regime from high temperatures to temperatures well inside the supercooled regime. By investigating the dynamics of both particle species on molecular and diffusive length scales along isochoric and isobaric pathways, we find a quadratic charge dependence of both $E_{\infty}$ and $T_{\text{g}}$, resulting in an approximately constant ratio of both quantities independent of the underlying observable, the thermodynamic ensemble, and the particle species, and this result is robust against the actual definition of $T_{\text{g}}$. This generic relation between the activation energy and the glass transition temperature indicates that high-temperature dynamics and the glassy slowdown are related phenomena, and the knowledge of $E_{\infty}$ may allow to approximately predict $T_{\text{g}}$.