Interdependence of Primary and Johari−Goldstein Secondary Relaxations in Glass-Forming Systems

Abstract

We report evidence from broadband dielectric spectroscopy that the dynamics of the primary alpha- and secondary Johari-Goldstein (JG) beta-processes are strongly correlated in different glass-forming systems over a wide temperature T and pressure P range, in contrast with the widespread opinion of statistical independence of these processes. The alpha-beta mutual dependence is quantitatively confirmed by (a) the overall superposition of spectra measured at different T-P combinations but with an invariant alpha-relaxation time; (b) the contemporary scaling of the isothermal-pressure and isobaric-temperature dependences of the alpha-and beta-relaxation times as plotted versus the reduced variable Tg(P)/T where Tg is the glass transition temperature. These novel and model-independent evidences indicate the relevance of the JG relaxation phenomenon in glass transition, often overlooked by most current theories.

Molecular Dynamics Study of Thermodynamic Scaling of the Glass-Transition Dynamics in Ionic Liquids over Wide Temperature and Pressure Ranges

“…Strong correlation between relaxation times of the R process and the Johari-Goldstein process in the scaled behaviors in both the temperature and pressure dependence has been pointed out 53,54 for glass-forming materials at temperatures above T g . Below T g , the relaxation times of both processes depends on the thermodynamic path in the formation of the glass.…”

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:…”

“…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.…”

“…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 .…”

“…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.…”