Molecular Mobility in Polymer Glasses Under Stress

技术概述：将进行主动变形过程中聚合物玻璃分子迁移率的测量。最近的研究结果表明，应力可以使玻璃中的节段流动性增加1000倍以上。这表明，塑性流动应被理解为应力产生足够的部分流动性，玻璃有效地转化为非常粘稠的液体。从这个角度来看，了解应力如何在玻璃中产生流动性是必须解决的关键问题，以便更好地预测聚合物玻璃的变形。在这项工作中，将测量聚甲基丙烯酸甲酯、聚碳酸酯、聚苯乙烯和完全固化的Epon环氧树脂在变形过程中的片段迁移率。除了单步拉伸蠕变测量外，还将进行多步蠕变和恒定应变率测量。先前的力学实验表明，聚合物玻璃的热力学历史对其后续变形有重要影响；例如，老化玻璃可以将延性反应转变为脆性破坏。预计这些现象都受到应力诱导迁移率的控制或显著影响，这一观点将通过测量不同时效时间后变形过程中的分子迁移率来验证。总的来说，这些实验将为聚合物玻璃的动力学提供新的见解，并提供更好地预测聚合物玻璃变形所需的数据。非技术总结：聚合物玻璃是一种重要的材料，在某些应用中，它们具有显著变形而不破裂的能力是一项关键属性。这项工作将测量变形如何加速聚合物链在玻璃中的移动速度；在广泛的应用中，需要这些信息来准确预测聚合物玻璃将如何变形。由于聚合物材料的广泛使用，这项工作可能会产生重大的经济和环境影响。例如，测量环氧树脂在变形过程中的迁移率变化，应该与制造更轻、更高效的飞机所需的先进复合材料的开发直接相关。此外，本提案的资金将通过整合材料研究和教育活动来推进研究生，本科生和高中生的培训。该基金资助的科学家和学生将与威斯康星大学麦迪逊分校合作。该项目旨在帮助来自弱势群体的高中生进入大学。每年夏天，这些受资助的人将为15名高中三年级学生提供30小时的高分子材料课程。PEOPLE项目在帮助学生在大学取得成功方面有着良好的记录；目前，威斯康星大学麦迪逊分校有220多名本科毕业生是PEOPLE项目的毕业生。在与一名高中科学老师的合作下，高分子材料暑期课程中的模块将被修改，以供威斯康星州公立高中使用。

TECHNICAL SUMMARY:Measurements of molecular mobility in polymer glasses during active deformation will be performed. Recent results show that stress can increase segmental mobility in a glass by more than a factor of 1000. This suggests that plastic flow should be understood as stress creating sufficient segmental mobility that the glass effectively is transformed into a very viscous liquid. From this perspective, understanding how stress creates mobility in a glass is the key issue that must be addressed in order to develop better predictions of polymer glass deformation. In this work, segmental mobility will be measured during the deformation of polymethylmethacrylate, polycarbonate, polystyrene, and a fully cured Epon epoxy resin. In addition to single step tensile creep measurements, multistep creep and constant strain-rate measurements will be performed. Previous mechanical experiments have shown an important influence of the thermal and mechanical history of polymer glasses on their subsequent deformation; aging a glass, for example, can transform a ductile response to brittle failure. It is anticipated that these phenomena are all controlled or significantly influenced by stress-induced mobility and this view will be tested with measurements of molecular mobility during deformation after various aging times. Collectively these experiments will provide new insights into the dynamics of polymer glasses and provide data needed to develop better predictions of polymer glass deformation.NON-TECHNICAL SUMMARY:Polymer glasses are important materials and, for some applications, their ability to deform significantly without breaking is a critical attribute. This work will measure how deformation accelerates the rate at which polymer chains can move in glass; this information is needed to make accurate predictions about how polymer glasses will deform in a wide range of applications. This work may have a significant economic and environmental impact because of the broad use of polymeric materials. As an example, measurements of mobility changes during the deformation of an epoxy resin should be directly relevant to the development of advanced composites needed to manufacture lighter, more efficient aircraft. In addition, the funding of this proposal will advance the training of graduate, undergraduate, and high school students through the integration of materials research and education activities. The scientists and students supported by this grant will work with the University of Wisconsin-Madison?s PEOPLE program to prepare high school students from under-represented groups for college. Each summer, those supported by this grant will staff a thirty-hour polymer materials course for 15 high school juniors. The PEOPLE program has a proven track record of preparing students to succeed in college; currently, the University of Wisconsin-Madison has more than 220 undergraduates who are graduates of the PEOPLE program. In collaboration with a high school science teacher, modules from the polymer materials summer course will be modified for use in Wisconsin public high schools.