Molecular mobility during polymer glass deformation

技术概述：聚合物玻璃的变形特性对应用至关重要，但在基础水平上却知之甚少。聚合物玻璃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力学响应的非线性密切相关；近似地说，聚合物玻璃的流动是由于聚合物段流动性的增加而成为可能的。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片段迁移率。温度在变形引起的迁移率中的作用将被研究。此外，利用反向应变变形，研究变形和老化在调整聚合物玻璃在势能图上的位置时的竞争关系。将评估变形过程中分段流动性的纯力学估计的有效性。提出的研究的总体目标是加强对聚合物玻璃变形的基本理解，并测试当前的理论方法和计算机模拟。对聚合物玻璃变形的更好理解也将影响对包括金属玻璃在内的其他玻璃材料变形的研究。非技术概述：聚合物玻璃由于其低密度、有用的机械性能和低成型所需的能量输入而在社会中发挥着重要作用。它们在日常生活中作为安全玻璃、防弹玻璃、汽车前照灯罩以及现代飞机（例如波音787）的主要结构部件而存在。在所有这些应用中，聚合物玻璃必须是坚硬的，但也不应在大的力响应破裂。威斯康星大学麦迪逊分校的这个项目寻求对这种行为的基本理解，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，特别是在轻质材料很重要的地方（例如，运输）。此外，本提案的资金将通过材料研究和教育活动的整合，推进研究生和高中生的培养。每年夏天，为教育推广而开发的高分子材料课程将作为30小时的课程呈现给15名高中三年级学生，其中大多数人来自工程和科学领域代表性不足的群体。这项拓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.