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 T g of ϳ181 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 1.08ϫ 10 −3 mol K / J in the glassy state at 120.4 K, which decreases slowly to 0.81 ϫ 10 −3 mol K / J at 176 K near T g and thereafter rapidly increases to 1.57ϫ 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 Ͼ T g 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.

Physical ageing and the Johari–Goldstein relaxation in molecular glasses

“…The initially slower increase in slope becomes more rapid as T g is approached on heating and reaches the slope for the liquid state. Similar relaxation features have been observed also for diethyl phthalate and there these were related to the configurational entropy [38].…”

Kinetic-freezing and unfreezing of local-region fluctuations in a glass structure observed by heat capacity hysteresis

“…76 Finally, the dielectric and mechanical relaxation spectra and the fixed frequency isochrones have shown that the JG relaxation peak height (or strength) decreases when T f is decreased. 8,9,26,[40][41][42][43][44][45][46][47][48] One expects a qualitatively similar decrease of the strength of the JG endotherm. Though the approach to the plateau-like value at T < T g in the plots of Figs.…”

Fast stochastic librations and slow small-angle rotations of molecules in glasses observed on nitroxide spin probes by stimulated electron spin echo spectroscopy

“…This suggestion of course requires appropriate theoretical consideration, which is however beyond the scope of the present paper. It is also interesting to note that mentioned s 0 values are of the same order as values for relaxation times for dielectric b-relaxation [1][2][3][4].…”

“…Molecular motions in glassy supercooled liquids have been studied using dielectric relaxation [1][2][3][4], nuclear magnetic resonance (NMR) [4][5][6][7], electron paramagnetic resonance (EPR) [8][9][10][11], and many other techniques. However, the microscopic nature of the phenomenon of glass transition is still unclear.…”