Istituto per i Processi Chimico Physici del CNR, Via G. Moruzzi 1, 56124 Pisa, Italy.
Department of Materials Science and Engineering, McMaster University, Hamilton, Ontario L8S 4L7, Canada.
J Phys Chem B. 2020 Mar 12;124(10):2017-2028. doi: 10.1021/acs.jpcb.9b10937. Epub 2020 Mar 3.
Experimental heat capacity, , of some physically aged polymers had shown an endothermic peak or a shoulder on heating when the material was still in the glassy state. In the first part of this paper, we report observation of a similar feature in a molecular glass, sucrose, indicating increase in the enthalpy and entropy from kinetic unfreezing of molecular motions in the solid state. Aging decreases of glass. Increase in the aging time, , or aging temperature, , interferes with the onset temperature of increase toward the liquid state value. When the endothermic feature is not obvious in the - plots of the glassy state, its presence may be discerned in a plot of d/d against . Molecular motions producing this feature have implications for the state point in a potential energy landscape of an aging . In the second part of the paper, we use the data to examine how much our violation of the Clausius theorem affects the entropy determined from the d ln integral. In addition to calculating this integral for a closed cycle of (irreversible) cooling and heating paths, we suggest an analysis which uses the δ d ln integrals (δ is the difference between the of the aged and the unaged glass) measured on the heating paths. The closed cycle d ln integral value is negligibly small. The δ d ln integral value increases with . It is equal to the enthalpy lost on aging divided by . Clausius theorem violation has no significant effect on determination of the entropy from d ln integral of an aged glass.
一些物理老化聚合物的实验比热容 在加热时，当材料仍处于玻璃态时，会出现吸热峰或肩峰。在本文的第一部分，我们报告了在分子玻璃蔗糖中观察到类似的特征，表明分子运动在固态的动力学冻结中增加了焓和熵。老化会降低玻璃的 。老化时间 或老化温度 的增加会干扰向液态状态值增加的起始温度。当玻璃态的 - 图中不明显时，其存在可以在 d/d 对 的图中识别出来。产生这种特征的分子运动对老化势能景观中的状态点有影响。在本文的第二部分，我们使用 数据来检查我们对克劳修斯定理的违反对从 d ln 积分确定的熵有多大影响。除了为（不可逆）冷却和加热路径的闭合循环计算此积分外，我们还建议了一种分析方法，该方法使用在加热路径上测量的 δ d ln 积分（δ 是老化和未老化玻璃的 之间的差异）。闭合循环 d ln 积分值可以忽略不计。δ d ln 积分值随 增加而增加。它等于老化过程中损失的焓除以 。克劳修斯定理的违反对从老化玻璃的 d ln 积分确定熵没有显著影响。
