Johari-Goldstein relaxation time with

Johari-Goldstein Relaxation Time with Crosslink Density... 

In the previous section, at temperatures above 7g, the Johari-Goldstein relaxation time has been shown to correspond well to the primitive relaxation time, and both are related to the structural a-relaxation time by Eq. (10). This equation should continue to hold at temperatures below T,. However, testing this relation in the glassy state is difficult because of either the scarcity or the unspecified thermal history of the data on the a-relaxation time xa. In fact, a reliable characterization of the structural relaxation can be acquired only at equilibrium, and such condition is rarely satisfied below Tg. Glassy systems are nonergodic, and their properties can depend on aging time and thermal history. Anyway, for glasses in isostructural state with a constant Active temperature Tf, both ra and To as well as Xjg should have Arrhenius dependences with activation enthalpies Ea, Eq, and Ejg respectively. Eq. (10) leads us to the relation... 

Abstract The present study demonstrates, by means of broadband dielectric measurements, that the primary a- and the secondary Johari-Goldstein (JG) /3-processes are strongly correlated, in contrast with the widespread opinion of statistical independence of these processes. This occurs for different glassforming systems, over a wide temperature and pressure range. In fact, we found that the ratio of the a- and P- relaxation times is invariant when calculated at different combinations of P and T that maintain either the primary or the JG relaxation times constant. The a-P interdependence is quantitatively confirmed by the clear dynamic scenario of two master curves (one for a-, one for P-relaxation) obtained when different isothermal and isobaric data are plotted together versus the reduced variable Tg(P)/T, where Tg is the glass transition temperature. Additionally, the a-P mutual dependence is confirmed by the overall superposition of spectra measured at different T-P combinations but with an invariant a-relaxation time. 

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