Corroborative evidences of TVgamma-scaling of the alpha-relaxation originating from the primitive relaxation/JG beta relaxation

TL;DR

This paper demonstrates that TVgamma-scaling of the alpha-relaxation in glass-formers originates from the primitive or Johari-Goldstein beta-relaxation, supported by experimental and simulation evidence, challenging previous assumptions about its structural relaxation origin.

Contribution

It reveals that TVgamma-scaling stems from the primitive relaxation, not the alpha-relaxation, providing new insights into the dynamic behavior of glass-formers and supporting the Coupling Model.

Findings

TVgamma-scaling is linked to primitive relaxation times.

All relaxation times share the same gamma and fractional Kohlrausch exponent.

Experimental and simulation data support the primitive relaxation origin of TVgamma-scaling.

Abstract

Successful thermodynamic scaling of the structural alpha-relaxation time or transport coefficients of glass-forming liquids determined at various temperatures T and pressures P means the data conform to a single function of the product variable TVgamma, where V is the specific volume and gamma is a material specific constant. In the past two decades we have witnessed successful TVgamma-scaling in many molecular, polymeric, and even metallic glass-formers, and gamma is related to the slope of the repulsive part of the intermolecular potential. The advances made indicate TVgamma-scaling is an important aspect of the dynamic and thermodynamic properties of glass-formers. In this paper we show the origin of TVgamma-scaling is not from the structural alpha-relaxation time. Instead it comes from its precursor, the Johari-Goldstein beta-relaxation or the primitive relaxation of the Coupling Model and their relaxation times or tau_0 respectively. It is remarkable that all relaxation times are functions of TVgamma with the same gama, as well as the fractional exponent of the Kohlrausch correlation function of the structural alpha-relaxation. We arrive at this conclusion convincingly based on corroborative evidences from a number of experiments and molecular dynamics simulations performed on a wide variety of glass-formers and in conjunction with consistency with the predictions of the Coupling Model.