From boiling point to glass transition temperature: transport coefficients in molecular liquids follow three-parameter scaling

TL;DR

This study introduces a three-parameter scaling approach to describe the temperature dependence of transport coefficients in molecular liquids across the glass transition, unifying high and low-temperature regimes.

Contribution

It proposes a novel three-parameter scaling model that captures the super-Arrhenius behavior of transport coefficients over the full temperature range in molecular glass formers.

Findings

The scaling successfully describes dielectric and light scattering data.

A single interaction parameter E_inf governs high-temperature behavior.

The model accounts for cooperative dynamics at low temperatures.

Abstract

The phenomenon of the glass transition is an unresolved problem of condensed matter physics. Its prominent feature, the super-Arrhenius temperature dependence of the transport coefficients remains a challenge to be described over the full temperature range. For a series of molecular glass formers, we combined tau(T) from dielectric spectroscopy and dynamic light scattering covering the range 10_-12 s < tau(T) < 10^2s. Describing the dynamics in terms of an activation energy E(T), we distinguish a high-temperature regime characterized by an Arrhenius law with a constant activation energy E_inf and a low-temperature regime for which E_coop(T):= E(T) - E_inf increases while cooling. A two-parameter scaling is introduced, specifically E_coop(T)/E_inf = f[lambda(T/T_A -1)], where f is an exponential function, lambda a dimensionless parameter, and T_A a reference temperature proportional to E_inf. In order to describe tau(T), in addition, the attempt time tau_inf has to be specified. Thus, a single interaction parameter E_inf extracted from the high-temperature regime together with lambda controls the temperature dependence of low-temperature cooperative dynamics.