聚合物玻璃在应力下的过老化？屈服应力更大但链段动力学更快！
Overaging with stress in polymer glasses? Faster segmental dynamics despite larger yield stress!
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中文总结 AI 辅助
该研究针对PMMA玻璃，发现应力下老化的样品屈服应力更高但链段动力学更快，修正了屈服应力与结构弛豫时间的简单函数关系及过老化的相关理论模型。
中文摘要 AI 辅助
众所周知，聚合物玻璃的物理老化会提高其屈服应力并影响其破坏行为。研究表明，与无应力的静置老化相比，老化过程中施加中等水平的应力会产生更高的屈服应力，这被解释为应力加速了物理老化，被称为过老化。本研究中，我们在应力下对PMMA玻璃进行老化，并利用探针取向技术直接测量老化过程中和老化后的链段动力学。我们观察到，应力下老化的样品尽管屈服应力更高，但应力释放后的链段动力学比静置老化的样品更快。这与此处探索的条件范围内的过老化解释相矛盾。我们的结果表明，屈服应力并非结构弛豫时间的简单函数，基于这一认识的理论模型需要修正。
英文摘要
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 PMMA glasses under stress, and carry out direct measurement of segmental dynamics during and after aging by 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.
