Correlation between primary and secondary Johari–Goldstein relaxations in supercooled liquids: Invariance to changes in thermodynamic conditions

Abstract

The primary alpha and the secondary Johari-Goldstein (JG) beta relaxations of supercooled glass-forming neat epoxy resin and 2-picoline in mixture with tristyrene are monitored by broadband dielectric relaxation spectroscopy at ambient pressure and elevated pressures. For different combinations of pressure and temperature that maintain the alpha-relaxation time constant, the frequency dispersion of the alpha relaxation is unchanged, as previously found in other glass-formers, but remarkably the JG beta-relaxation time remains constant. This is more clear evidence of a strong connection between the alpha- and JG beta-relaxation times, a fact that should be taken into account in the construction of a viable theory of glass transition.

The component dynamics of miscible binary mixtures of glass formers: New features

“…Several previous experimental studies [15,16,[18][19][20][21][22] and simulations have verified two simultaneous CM predictions in mixtures where the host has a significantly higher T g than the guest. They are:…”

“…Remarkably, the connection is passed onto the α-and JG β-relaxations of a component in mixtures of two van der Waals glass-formers. An example is the invariance of the ratio of τ αg to τ JG,g , the relaxation time of the JG β-relaxation, to widely different combinations of pressure and temperature that maintain τ α,g constant [15][16]. This is a remarkable result because in these experiments the specific volume varies over a significant range, and yet τ αg /τ JG,g is invariant at constant τ αg .…”

“…We used for fitting a simple superposition of the two processes, usually performed in literature but arbirtary and strongly questionable, since the two processes are interrelated as shown in ref. [12,15,16]. Of course, when two processes are so close each other, no unequivocal procedure of deconvoluton is possible; but it is clear that any estimation of the true broadness of the α-peak should result in a narrower (or at least equal) shape than that of the convoluted peaks.…”

“…This is a remarkable result because in these experiments the specific volume varies over a significant range, and yet τ αg /τ JG,g is invariant at constant τ αg . So far, there is only one [6,[15][16][17]. In all mixtures considered thus far, the guest in its pure state has a lower glass transition temperature than that of the host.…”

Double Primary Relaxation in a Highly Anisotropic Orientational Glass-Former with Low-Dimensional Disorder

“…31 The frequency separation between the α relaxation process and such secondary relaxation has been shown to be invariant under isochronal conditions within the temperature-pressure diagram. 32 These studies have thus concluded that the EW is a "precursor" Johari Goldstein relaxation, as shown e.g. for the case of glycerol, 31 ethanol, 17 and propylene glycol oligomers.…”