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首页> 外文期刊>The Journal of Chemical Physics >The temperature dependence of free volume in phenyl salicylate and its relation to structural dynamics: A positron annihilation lifetimeand pressure-volume-temperature study
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The temperature dependence of free volume in phenyl salicylate and its relation to structural dynamics: A positron annihilation lifetimeand pressure-volume-temperature study

机译：水杨酸苯酯中自由体积的温度依赖性及其与结构动力学的关系：正电子an没寿命和压力-体积-温度研究

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摘要

Positron annihilation lifetime spectroscopy (PALS) and pressure-volume-temperature (PVT)experiments were performed to characterize the temperature dependent microstructure of the holefree volume in the low molecular weight glass-former phenyl salicylate (salol). The PALS spectrawere analyzed with the new routine LT9.0and the volume distribution of subnanometer size holescharacterized by its mean and standard deviation σh was calculated. Crystallization of theamorphous sample was observed in the temperature range above 250 K, which leads to a vanishingof the positronium formation. The positronium signal recovered after melting at 303 K. Acombination of PALS with PVT data enabled us to calculate the specific density N'h, the specificvolume Vf, and the fraction of holes fh in the amorphous state. From comparison with dielectricmeasurements in the temperature range above TB=265 K, it was found that the primary structuralrelaxation slows down with temperature, faster than the shrinkage of the hole free volume Vf wouldpredict, on the basis of the Cohen-Turnbull (CT) free volume theory. CT plots can be linearized byreplacing Vf of the CT theory by (Vf-ΔV), where ΔV is a volume correction term. This wasinterpreted as indication that the lower wing of the hole size distribution contains holes too small toshow a liquidlike behavior in their surroundings. Peculiarities of the relaxation behavior belowTB=265 K and the possible validity of the Cohen–Grest free volume model are discussed.
机译：进行了正电子an没寿命谱（PALS）和压力-体积-温度（PVT）实验，以表征低分子量玻璃状水杨酸苯酯（salol）中无孔体积的温度依赖性微观结构。用新的程序LT9.0分析了PALS光谱，并计算了以其平均和标准偏差σh为特征的亚纳米尺寸孔的体积分布。在高于250 K的温度范围内观察到非晶态样品的结晶，这导致了正电子形成的消失。正电子信号在303 K熔化后恢复。PALS与PVT数据的结合使我们能够计算出非晶态下的比密度N'h，比体积Vf和空穴fh的分数。通过与TB = 265 K以上温度范围内的介电测量结果进行比较，发现在无Cohen-Turnbull（CT）的基础上，主要结构松弛随温度降低，快于无孔体积Vf的收缩速度体积理论。通过将CT理论的Vf替换为（Vf-ΔV），可以将CT图线性化，其中ΔV是体积校正项。这被解释为指示孔尺寸分布的下部机翼包含的孔太小而无法在其周围环境中显示出类似液体的行为。讨论了TB = 265 K以下的松弛行为的特殊性和Cohen-Grest自由体积模型的可能有效性。

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