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

The primary α and the secondary Johari–Goldstein (JG) β 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 α-relaxation time constant, the frequency dispersion of the α relaxation is unchanged, as previously found in other glass-formers, but remarkably the JG β-relaxation time remains constant. This is more clear evidence of a strong connection between the α- and JG β-relaxation times, a fact that should be taken into account in the construction of a viable theory of glass transition. [ABSTRACT FROM AUTHOR]