The Johari-Goldstein beta-relaxation of glass-forming binary mixtures RID A-8503-2012

The present paper shows, by means of broadband dielectric measurements, that the primary alpha- and the secondary Johari-Goldstein (JG) beta-processes in binary mixtures are strongly correlated. This occurs for different polar rigid probes dissolved in apolar glass-forming solvents, over a wide temperature and pressure range. reserved. We found that the coupling parameter n = 1 - beta(KWW) and the ratio between alpha- and beta-relaxation time reduce on increasing the size of the solute solved within the same apolar matrix. Moreover, such a ratio is invariant when calculated at different combinations of P and T maintaining either the primary or the JG relaxation times constant. Dielectric spectra measured at different T-P combinations but with an invariant alpha-relaxation time are well superposed in both the alpha- and beta-frequency ranges. Experimental results can be rationalized by Coupling Model equation. (C) 2010 Elsevier B.V. All rights reserved