Power G, Vij J K, Johari G P
Institute of Advanced Materials Science, Department of Electronic and Electrical Engineering, Trinity College, University of Dublin, Dublin 2, Ireland.
J Chem Phys. 2006 Jan 28;124(4):044513. doi: 10.1063/1.2159473.
Dielectric spectra of the beta relaxation in glassy and ultraviscous liquid diethyl phthalate show that its relaxation strength Delta epsilon(beta), the distribution of times, and the relaxation rate are more sensitive to temperature T in the ultraviscous liquid than in the glassy state. The Delta epsilon(beta) against temperature plot has an elbow-shaped break near T(g) of approximately 181 K, which is remarkably similar to that observed in the entropy, enthalpy, and volume against temperature plots, and in the plot of Delta epsilon(beta) against the liquid's entropy minus its 0 K value. The ratio of Delta epsilon(beta) to diethyl phthalate's entropy, after subtracting the 0 K value, is 1.08 x 10(-3) mol K/J in the glassy state at 120.4 K, which decreases slowly to 0.81 x 10(-3) mol K/J at 176 K near T(g) and thereafter rapidly increases to 1.57 x 10(-3) mol K/J at 190 K. Variation in Delta epsilon(beta) parallels the variation of the entropy. A change in the activation energy of the beta process at T>T(g) indicates that its rate is also determined by the structure of the ultraviscous liquid. Features of beta relaxation are consistent with localized motions of molecules and may not involve small-angle motions of all molecules.
玻璃态和超粘性液态邻苯二甲酸二乙酯中β弛豫的介电谱表明，与玻璃态相比，其弛豫强度Δε(β)、时间分布和弛豫速率在超粘性液体中对温度T更为敏感。Δε(β)随温度的变化曲线在约181K的玻璃化转变温度T(g)附近有一个肘形转折，这与在熵、焓和体积随温度的变化曲线以及Δε(β)随液体熵减去其0K值的变化曲线中观察到的情况非常相似。在120.4K的玻璃态下，减去0K值后，Δε(β)与邻苯二甲酸二乙酯熵的比值为1.08×10⁻³mol K/J，在接近T(g)的176K时缓慢降至0.81×10⁻³mol K/J，此后在190K时迅速增至1.57×10⁻³mol K/J。Δε(β)的变化与熵的变化平行。在T>T(g)时β过程活化能的变化表明其速率也由超粘性液体的结构决定。β弛豫的特征与分子的局域运动一致，可能不涉及所有分子的小角运动。
