Orientation polarization from faster motions in the ultraviscous and glassy diethyl phthalate and its entropy

Abstract

Dielectric spectra of the relaxation in glassy and ultraviscous liquid diethyl phthalate show that its relaxation strength , the distribution of times, and the relaxation rate are more sensitive to temperature T in the ultraviscous liquid than in the glassy state. The against temperature plot has an elbow-shaped break near Tg of ~181 K, which is remarkably similar to that observed in the entropy, enthalpy, and volume against temperature plots, and in the plot of against the liquid's entropy minus its 0 K value. The ratio of to diethyl phthalate's entropy, after subtracting the 0 K value, is 1.08?10?3 mol K/J in the glassy state at 120.4 K, which decreases slowly to 0.81?10?3 mol K/J at 176 K near Tg and thereafter rapidly increases to 1.57?10?3 mol K/J at 190 K. Variation in parallels the variation of the entropy. A change in the activation energy of the process at T>Tg indicates that its rate is also determined by the structure of the ultraviscous liquid. Features of relaxation are consistent with localized motions of molecules and may not involve small-angle motions of all molecules