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

Abstract Successful thermodynamic scaling of the structural α-relaxation time τα 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 TVγ, where V is the specific volume and γ is a material specific constant. In the past two decades we have witnessed successful TVγ-scaling in many molecular, polymeric, and even metallic glass-formers, and γ is related to the slope of the repulsive part of the intermolecular potential. The advances made indicate TVγ-scaling is an important aspect of the linked dynamic and thermodynamic properties of glass-formers. In this paper we show the origin of TVγ-scaling is not from the structural α-relaxation times τα. Instead it comes from its precursor, the Johari-Goldstein (JG) β-relaxation or the primitive relaxation of the Coupling Model, and their relaxation times τβ or τ0 respectively. It is remarkable that all relaxation times,τα τβ and τ0 are functions of TVγ with the same γ, as well as the fractional exponent βK of the Kohlrausch correlation function of the structural α-relaxation. We arrive at these conclusions 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 the consistency with the predictions of the Coupling Model. The conclusions have significant impact on the glass transition problem. This is because the origin of the thermodynamic properties of the α-relaxation lies in the JG β-relaxation/primitive relaxation, and also the inseparable connection in dynamics properties between the former and the latter established elsewhere.