老化加速 vs 过老化：循环加载/卸载对PMMA玻璃链段动力学的影响
Rejuvenation versus overaging: The effect of cyclic loading/unloading on the segmental dynamics of PMMA glasses
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中文总结 AI 辅助
该研究探究循环加载/卸载对PMMA玻璃链段动力学和力学性能的影响，采用探针再取向技术等方法，发现未出现过老化，探针再取向技术可灵敏检测变形非线性效应。
中文摘要 AI 辅助
在聚合物和胶体玻璃的实验与模拟中，已报道了变形加速结构弛豫或物理老化的现象，即过老化，正确考虑过老化对预测聚合物玻璃在工程应用中的长期行为至关重要。本研究分别采用探针再取向技术和力学响应的老化时间叠加法，探究循环加载/卸载对PMMA玻璃链段动力学和力学性能的影响。在Tg - 10 K至Tg - 25 K的温度范围内，开展了5000次拉伸加载/卸载循环，循环伸长应变范围为0.003至0.007。循环后，采用探针再取向技术测得的链段动力学与未变形样品相比，要么保持不变，要么更快。循环后玻璃的弛豫时间在约其老化时间的共同时间尺度上恢复，表明它们保留了原始老化状态的记忆，而非完全消除了热和力学历史。令人惊讶的是，循环导致的变化在探针再取向测量中比在力学性能中更明显，这说明探针再取向技术能够灵敏地检测变形的非线性效应。在这些循环加载/卸载实验的光学或力学测量中，未观察到过老化的证据。
英文摘要
The acceleration of structural relaxation or physical aging by deformation, known as overaging, has been reported in experiments and simulations of polymer and colloid glasses, and correctly accounting for overaging is important for the prediction of the long-term behavior of polymer glasses in engineering applications. Here the effects of cyclic loading/unloading on the segmental dynamics and mechanical properties of PMMA glasses are investigated using a probe reorientation technique and time-aging time superposition of the mechanical response, respectively. Sets of 5000 tensile loading/unloading cycles were performed at temperatures between Tg - 10 K and Tg - 25 K with cycle extension strains ranging from 0.003 to 0.007. After cycling, the segmental dynamics measured with the probe reorientation technique either remained unchanged or were faster relative to an undeformed sample. The relaxation times of cycled glasses recovered with a common time scale on the order of their aging time, indicating that they retain a memory of their original age, as opposed to a full erasure of their thermal and mechanical history. Surprisingly, changes as a result of cycling were more obvious in probe reorientation measurements than in the mechanical properties, suggesting that the probe reorientation technique can sensitively detect nonlinear effects of deformation. No evidence of overaging was observed in the optical or mechanical measurements as a result of these cyclic loading/unloading experiments.
