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

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