Molecular Mobility in Polycarbonate Glasses During Active Deformation

技术概述：当聚合物玻璃变形时，即使样品温度没有明显变化，玻璃中的分子迁移率也可以提高许多数量级。威斯康星大学麦迪逊分校的研究人员将使用最近开发的光学光漂白技术来量化聚碳酸酯玻璃变形过程中分子迁移率的变化。在现有模型的框架内，迁移率的变化是导致聚合物玻璃非线性力学响应的原因。在变形过程中，系统在势能景观上的位置可以改变。了解这些变化是这项工作的中心目标，因为它对提高对聚合物玻璃变形的理解至关重要。恒定应变速率和恒定应力变形都将被利用。恒定应变速率实验提供了对产率的控制，从而允许在系统被拉到能量景观时观察分子迁移率的变化。应力老化实验被解释为系统被拉下了能源景观；应力老化过程中的流动性测量将验证这一解释。将实验结果与模拟结果和模型预测结果进行比较，可以提高对玻璃变形的基本理解，提高预测能力。非技术概述：聚合物玻璃在我们的社会中应用广泛。这些材料可以在日常生活中看到，如防弹玻璃、光盘、安全眼镜和汽车前灯罩。在波音787等下一代商用飞机上，机翼和机身将由聚合物玻璃（与其他材料复合）制成。对于这些应用，聚合物玻璃被使用，因为它们在压力下变形而不破裂的能力。通过增加我们对聚合物玻璃变形的基本理解，威斯康星大学麦迪逊分校的这项研究项目可能会提高预测聚合物玻璃机械性能的能力。更好的预测，反过来，将导致这些材料在运输部门等领域的进一步应用，轻质材料节省能源，从而有助于减少温室气体排放。每年，这些研究人员将为15名高中生进行为期三周的暑期充实课程，其中大多数学生将来自科学和工程领域代表性不足的群体。每天两个小时，这些研究人员将提供旨在提高学生对科学/工程的兴趣，并培养在大学取得成功所需的关键技能的活动。

TECHNICAL SUMMARY:When a polymer glass is deformed, molecular mobility in the glass can be enhanced by many orders of magnitude even when the sample temperature does not change appreciably. Researchers from the University of Wisconsin-Madison will use a recently developed optical photobleaching technique to quantify changes in molecular mobility during the deformation of polycarbonate glasses. Within the framework of current models, changes in mobility are responsible for the non-linear mechanical response of polymer glasses. During deformation, the position of the system on the potential energy landscape can be altered. Understanding these changes is the central objective of this work because it is critical for an improved understanding of polymer glass deformation. Both constant strain-rate and constant stress deformations will be utilized. Constant strain-rate experiments provide controlled access to yield and thus allow changes in molecular mobility to be observed as the system is pulled up the energy landscape. Stress-aging experiments have been interpreted as the system being pulled down the energy landscape; mobility measurements during stress-aging will test this interpretation. The comparison of experimental results with simulations and model predictions should result in an increased fundamental understanding of glass deformation and better prediction capabilities. NON-TECHNICAL SUMMARY:Polymer glasses are widely used in our society. These materials can be seen everyday as bulletproof glass, compact disks, safety glasses, and automobile headlamp covers. In next generation commercial aircraft such as the Boeing 787, the wings and fuselage will be made of polymer glass (in a composite with other materials). For such applications, polymer glasses are used because of their ability to deform under stress without breaking. By increasing our fundamental understanding of polymer glass deformation, this research project at the University of Wisconsin-Madison will likely lead to an improved ability to predict the mechanical properties of polymer glasses. Better predictions, in turn, will lead to further applications for these materials in areas like the transportation sector, where lightweight materials save energy and thus contribute to a decrease in greenhouse gas emissions. Each year, these researchers will conduct a three-week summer enrichment course for 15 high school students, most of whom will be from groups underrepresented in science and engineering. For two hours each day, these researchers will provide activities designed to increase interest in science/engineering and to develop critical skills required for success in college.