Positronium annihilation lifetimes and dielectric spectroscopy studies on diethyl phthalate: Phenomenological correlations and microscopic analyses in terms of the extended free volume model by Cohen-Grest

摘要

A combined positronium annihilation lifetime spectroscopy (PALS) and dielectric spectroscopy (DS) study on a typical van der Waals glass-former diethyl phthalate (DEP) was performed and the results were compared. From phenomenological point of view, the mutual relationships between the characteristic PALS temperatures, the glass temperature T-g(PALS), and the crossover temperatures T-b1(L) and T-b2(L) on the ortho-positronium (o-Ps) lifetime versus the temperature plot, have been discussed with respect to the characteristic DS temperatures, the glass temperature T-g(DS) and the dynamic crossover temperature T-B(ST), concerning the crossover behavior of primary alpha-relaxation times. Next, simultaneous application of the extended free volume (EFV) model by Cohen-Grest on the temperature dependence of both the mean free volume hole size data as extracted from PALS and the dielectric alpha-relaxation time revealed a good agreement between the experimental T-b1(L) and the characteristic EFV temperatures T-0(DS) and T-0(PALS) at which a free volume percolation should occur. These results indicate the important role of free volume in control of the primary (alpha) dynamics of supercooled DEP.