Overaging with Stress in Polymer Glasses? Faster Segmental Dynamics despite Larger Yield Stress!
Overaging with Stress in Polymer Glasses? Faster Segmental Dynamics despite Larger Yield Stress!
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DOI：
10.1021/acs.macromol.2c01338
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发表时间：
2022-11
期刊：
影响因子：
5.5
通讯作者：
M. Razavi;Enran Xing;M. Ediger
中科院分区：
文献类型：
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作者：
M. Razavi;Enran Xing;M. Ediger
众所周知，聚合物玻璃的物理老化会增加其屈服应力并影响其失效行为。研究表明，与无应力老化（静态老化）相比，在老化过程中施加中等水平的应力会导致更高的屈服应力。这被解释为表明压力加速了身体老化，并被描述为过度老化。在这项研究中，我们年龄的聚（甲基丙烯酸甲酯）（PMMA）玻璃的应力和进行直接测量的节段动态老化过程中和老化后，使用探针重定向技术。我们观察到，应力下老化的样品，尽管有较高的屈服应力，有更快的节段动力学应力释放后，比静态老化的样品。这与过度老化的解释相矛盾，因为这里探讨的条件范围。我们的研究结果表明，屈服应力是不是一个简单的函数的结构松弛时间和理论模型的基础上，这种理解需要进行修订。
It is well known that physical aging of polymer glasses increases their yield stress and affects their failure behavior. Studies indicate that application of moderate levels of stress during aging results in higher yield stress compared to aging in the absence of stress (quiescent aging). This has been interpreted to indicate that stress accelerates physical aging and has been described as overaging. In this study, we age poly(methyl methacrylate) (PMMA) glasses under stress and carry out direct measurement of segmental dynamics during and after aging using a probe reorientation technique. We observe that samples aged under stress, despite having higher yield stress, have faster segmental dynamics after stress release than quiescently aged samples. This contradicts the overaging interpretation, for the range of conditions explored here. Our results indicate that yield stress is not a simple function of structural relaxation time and theoretical models based on this understanding need to be revised.