Scaling of the Local Dynamics and the Intermolecular Potential

TL;DR

This paper explores methods to determine the scaling exponent g in supercooled liquids and polymers, linking it to intermolecular potentials and thermodynamic properties, enabling analysis of dynamics without high-pressure relaxation data.

Contribution

It introduces new approaches to determine the scaling exponent g from molecular and thermodynamic data, bypassing the need for high-pressure relaxation measurements.

Findings

g can be related to the Gruneisen parameter.

g can be obtained from pressure-volume-temperature data.

Methods enable analysis of dynamics at various P and V without relaxation measurements.

Abstract

The experimental fact that relaxation times, tau, of supercooled liquids and polymers are uniquely defined by the quantity TV^g, where T is temperature, V specific volume, and g a material constant, leads to a number of interpretations and predictions concerning the dynamics of vitrification. Herein we examine means to determine the scaling exponent g apart from the usual superpositioning of relaxation data. If the intermolecular potential can be approximated by an inverse power law, as implied by the TV^g scaling, various equations are derived relating g to the Gruneisen parameter and to a common expression for the pressure derivative of the glass temperature. In addition, without assumptions, g can be obtained directly from pressure-volume-temperature data. These methods for determining g from molecular or thermodynamic properties are useful because they enable the P- and V-dependences of tau to be obtained, and thereby various analyses of the dynamics to be explored, without the need to carry out relaxation measurements beyond ambient pressure.