Corroborative evidences of TVγ-scaling of the α-relaxation originating from the primitive relaxation/JG β relaxation

Abstract

Successful thermodynamic scaling of the structural -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 TV  , where V is the specific volume and  is a material specific constant. In the past two decades we have witnessed successful TV  -scaling in many molecular, polymeric, and even metallic glass-formers, and  is related to the slope of the repulsive part of the intermolecular potential. The advances made indicate TV  -scaling is an important aspect of the dynamic and thermodynamic properties of glass-formers. In this paper we show the origin of TV  -scaling is not from the structural -relaxation time   . Instead it comes from its precursor, the Johari-Goldstein -relaxation or the primitive relaxation of the Coupling Model and their relaxation times   or 0 respectively. It is remarkable that all relaxation times,    and 0 are functions of TV  with the same , as well as the fractional exponent K of the 2 Kohlrausch correlation function of the structural -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.

Why is the change of the Johari–Goldstein β-relaxation time by densification in ultrastable glass minor?

“…The property of the invariance of the ratio t a (T,P)/t b (T,P) to variations of T and P while keeping t a (T,P) constant [20][21][22][23][24][25][26][27] is key to arriving at the results in Section (A). It also has the immediate consequence that t b is also a function of r g /T, if t a is a function of r g /T, although the two functions t b = f b (r g /T) and t a = F a (r g /T) are different.…”

“…As mentioned in the Introduction, to explain the properties of the JG b-relaxation in USG compared with the OG we shall apply two general dynamic and thermodynamic properties of the a-relaxation and JG b-relaxation established before from studies at elevated pressures in molecular glass-formers. [20][21][22][23][24][25][26][27] The application is justified by the fact that density is increased at elevated pressure, and the increase can be comparable to or even larger than that in USG. Through the application, we are able to explain why the Johari-Goldstein (JG) b-relaxation time, t b , in USG of toluene, 13 etoricoxib 14 and telmisartan 15 is about an order of magnitude longer than that in OG, and has nearly the same activation energy E b .…”

“…These changes are comparable to or larger than those achieved by producing USG. Found in general in many molecular glassformers [20][21][22][23][24][25][26][27][28] is the approximate invariance of t b (T,P) to variations of P and T provided t a (T,P) are kept constant. Examples of experimental evidence for this property in OG are shown in Fig.…”

“…Notwithstanding, the much smaller changes of t b and E b by densification in USG are in stark contrast to the behavior of the a-relaxation time t a , and this remarkable experimental observation deserves an explanation. In this paper, we provide an explanation based on two general properties established from the studies of glasses and liquids at elevated pressures [20][21][22][23][24][25][26][27] and applied it to USG. The increase in density of the glasses formed under high pressure can be even larger than that in USG, and hence the general properties should apply.…”

Molecular dynamics and the translational–rotational coupling of an ionically conducting glass-former: amlodipine besylate

“…The existence and universal presence of this kind of secondary relaxation, called the Johari-Goldstein (JG) b-relaxation, was suggested by its analogy to the primitive relaxation of the CM, which started in a paper 47 in 1998, and has since been extensively developed. 25,[48][49][50][51][52][53] The CM 54 has the following exact relation between the primitive relaxation time s 0 and the a-relaxation time s a ,…”