Molecular mobility during polymer glass deformation

技术概述：聚合物玻璃的变形性能对应用至关重要，但在基础水平上人们对其了解很少。聚合物玻璃的变形几乎总是非线性的，并且由于材料初始状态的非平衡性质而变得复杂。聚合物玻璃变形过程中分子迁移率的变化与机械响应的非线性密切相关；从第一个近似值来看，聚合物玻璃的流动可能是由于聚合物链段流动性的增加。威斯康星大学麦迪逊分校的研究人员将使用光学技术直接测量聚甲基丙烯酸甲酯和聚苯乙烯玻璃变形过程中的链段迁移率。温度在形变诱导迁移率中的作用将被研究。此外，还将利用应变反转形变来研究变形和老化在调整聚合物玻璃在势能景观上的位置方面的竞争。将对变形过程中节段流动性的纯机械估计的有效性进行评估。拟议研究的总体目标是加强对聚合物玻璃变形的基本了解，并测试当前的理论方法和计算机模拟。更好地了解聚合物玻璃的变形也将影响包括金属玻璃在内的其他玻璃材料的变形研究。非技术摘要：聚合物玻璃由于其低密度、有用的机械性能和成型所需的低能量输入，在社会上扮演着重要的角色。它们在日常生活中用作安全玻璃、防弹玻璃、汽车前照灯盖，以及现代飞机(如波音787)的主要结构部件。在所有这些应用中，聚合物玻璃必须是坚硬的，但也不应该在大的力作用下破裂。威斯康星大学麦迪逊分校的这个项目试图从根本上理解这种行为，并可能提高预测聚合物玻璃对各种力的反应的能力。更好的预测有望导致这些材料的新应用，特别是在轻质材料非常重要的领域(例如运输)。此外，这项建议的资金将通过材料研究和教育活动的整合来推进研究生和高中生的培训。每年夏天，为推广教育而开发的聚合物材料课程将以30小时的课程形式提供给15名高三学生，他们中的大多数将来自工程和科学领域代表性不足的群体。这项外展计划的目标是培养学生对科学/工程的兴趣，并培养在大学取得成功所需的技能。

TECHNICAL SUMMARY:The deformation properties of polymer glasses are critical for applications but are poorly understood at a fundamental level. Polymer glass deformation is almost always non-linear and is complicated by the non-equilibrium nature of the initial state of the material. Changes in molecular mobility during the deformation of a polymer glass are intimately connected with the nonlinearity of the mechanical response; to a first approximation, the flow of a polymer glass is made possible by the increased mobility of polymer segments. Researchers from the University of Wisconsin-Madison will use an optical technique to directly measure segmental mobility during the deformation of poly(methyl methacrylate) and polystyrene glasses. The role of temperature in deformation-induced mobility will be investigated. In addition, using reversing strain deformations, the competition between deformation and aging in adjusting the position of the polymer glass on the potential energy landscape will be investigated. The validity of purely mechanical estimates of segmental mobility during deformation will be evaluated. The overall objectives of the proposed research are to enhance the fundamental understanding of polymer glass deformation and to test current theoretical approaches and computer simulations. A better understanding of polymer glass deformation will also influence research on the deformation of other glassy materials including metallic glasses.NON-TECHNICAL SUMMARY:Polymer glasses play an important role in society due to their low density, their useful mechanical properties, and the low energy input required for molding. They are encountered in everyday life as safety glasses, bulletproof glass, automobile headlamp covers, and as major structural components in modern aircraft (e.g., the Boeing 787). In all these applications, the polymer glass must be stiff but also should not break in response to large forces. This project at the University of Wisconsin-Madison seeks a fundamental understanding of this behavior and will likely lead to an improved ability to predict the response of polymer glasses to various forces. Better predictions are expected to lead to new applications for these materials particularly where lightweight materials are important (e.g., transportation). In addition, the funding of this proposal will advance the training of graduate students and high school students, through the integration of materials research and education activities. Each summer a polymer materials curriculum, developed for educational outreach, will be presented as a thirty-hour course for 15 high school juniors, most of whom will be from groups that have been underrepresented in engineering and science. The goal of this outreach program is to develop interest in science/engineering and to develop skills required for success in college.