Positron-annihilation-lifetime response and broadband dielectric relaxation spectroscopy: Diethyl phthalate

Abstract

We report the results of a combined phenomenological analysis of the data from positron-annihilation-lifetime spectroscopy (PALS) and the relaxation data from broadband dielectric spectroscopy (BDS) on diethyl phthalate (DEP). The ortho-positronium (o -Ps) lifetime, τ3, as a function of temperature over a temperature range from 67 K up to 300 K is compared with the spectral features and the relaxation parameters of the BDS spectra decomposed into the primary α and the secondary β processes in the temperature range from 140 K up to 380 K by using the Williams-Watts scheme. Phenomenological model-free analysis of the τ3 -T plot provides the three characteristic PALS temperatures, where the two most pronounced ones at TgPALS =185 K and Tb2 =245 K=1.32 TgPALS are related to the glass-liquid transition and the onset of a quasiplateau region, respectively. In the case of a weaker bend effect at Tb1 =210 K=1.14 TgPALS, a number of new coincidences with changes in the dielectric β process have been found. They concern the changes in width parameter of the distribution function for the β relaxation time and the activation energy of the βeff process, a crossover from the Arrhenius to the non-Arrhenius type of temperature dependence as well as with the onset of a short-time tail of the β relaxation time distribution and finally, with changes in the relaxation strength of the α and βeff processes. All these findings indicate a close connection of the o -Ps annihilation parameters and relaxation characteristics of BDS response for the DEP matrix. © 2007 The American Physical Society.