Segmental Dynamics in the Strain-Hardening Regime for Poly(methyl methacrylate) Glasses with and without Melt Stretching
Segmental Dynamics in the Strain-Hardening Regime for Poly(methyl methacrylate) Glasses with and without Melt Stretching
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DOI：
10.1021/acs.macromol.2c01442
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发表时间：
2022-09
期刊：
影响因子：
5.5
通讯作者：
Enran Xing;Trevor Bennin;M. Razavi;M. Ediger
中科院分区：
文献类型：
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作者：
Enran Xing;Trevor Bennin;M. Razavi;M. Ediger
应变硬化是聚合物玻璃在大变形过程中的一个特征，这有助于稳定玻璃以防止破裂。在实验上，人们对应变硬化过程中的分段动力学知之甚少，这些数据对于建立在此状态下变形的聚合物玻璃的分子水平理论非常重要。在这里，我们使用光漂白技术，测量了有和没有熔融拉伸的轻度交联聚甲基丙烯酸甲酯（PMMA）玻璃的链段动力学，这些玻璃变形为应变硬化状态，局部工程应变率为10-4.6至10-4s-1atTg-23 K和Tg-33 K。我们发现，熔融拉伸PMMA玻璃表现出更突出的应变硬化特征和更快的链段动力学，大约是与未进行熔融拉伸的 PMMA 相比，减少 15%。在给定的真实应变率下，在深度应变硬化状态下，没有熔融拉伸的 PMMA 的分段动力学从刚刚超过屈服值的值加速，在 0.8 真实应变时加速高达 40%。我们的观察结果与之前发布的模拟结果一致。
Strain hardening is a feature of polymer glasses during large deformation, which helps to stabilize the glasses against breakage. Experimentally, little is known about the segmental dynamics during strain hardening, and such data are important for building a molecular-level theory of polymer glasses deformed in this regime. Here, using a photobleaching technique, we measured the segmental dynamics of lightly crosslinked poly(methyl methacrylate) (PMMA) glasses with and without melt stretching, which were deformed into the strain-hardening regime with local engineering strain rates from 10–4.6to 10–4s–1atTg-23 K andTg-33 K. We find that melt-stretched PMMA glasses show a more prominent strain-hardening feature and faster segmental dynamics by a factor of about 15% compared to PMMA without melt stretching. At a given true strain rate, the segmental dynamics of PMMA without melt stretching are accelerated in the deep strain-hardening regime from the value just beyond yield, by up to 40% at 0.8 true strain. Our observations are in agreement with previously published simulation results.