Molecular Mobility in Polymer Glasses Under Stress

技术总结：将在主动变形过程中测量聚合物玻璃中的分子迁移率。 最近的研究结果表明，应力可以使玻璃中的链段迁移率增加1000倍以上。 这表明塑性流动应理解为产生足够的节段流动性的应力，使得玻璃有效地转化为非常粘稠的液体。 从这个角度来看，理解应力如何在玻璃中产生流动性是为了更好地预测聚合物玻璃变形而必须解决的关键问题。在这项工作中，将测量的聚甲基丙烯酸甲酯，聚碳酸酯，聚苯乙烯，和一个完全固化的Epon环氧树脂的变形过程中的链段流动性。 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。 先前的机械实验已经显示出聚合物玻璃的热和机械历史对其随后的变形的重要影响;例如，老化玻璃可以将韧性响应转变为脆性失效。 预计这些现象都受到应力诱导迁移率的控制或显著影响，并且将在各种老化时间后的变形过程中通过测量分子迁移率来测试这一观点。 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。非技术摘要：聚合物玻璃是重要的材料，对于某些应用，它们在不断裂的情况下显著变形的能力是一个关键属性。 这项工作将测量变形如何加速聚合物链在玻璃中移动的速率;需要这些信息来准确预测聚合物玻璃在广泛的应用中将如何变形。 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，测量环氧树脂变形过程中的迁移率变化，应与制造更轻、更高效飞机所需的先进复合材料的开发直接相关。 此外，该提案的资金将通过材料研究和教育活动的整合，促进研究生、本科生和高中生的培训。 科学家和学生支持这项赠款将与威斯康星大学麦迪逊分校？的人计划，以准备高中学生从代表性不足的群体上大学。 每年夏天，那些由这笔赠款支持的人员将为15名高中三年级学生提供30小时的聚合物材料课程。 人民计划有一个良好的记录，准备学生在大学取得成功;目前，威斯康星大学麦迪逊分校有超过220名本科生谁是人民计划的毕业生。 在与高中科学教师合作，从聚合物材料夏季课程的模块将被修改用于威斯康星州公立高中。

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.