Molecular Mobility in Polycarbonate Glasses During Active Deformation

技术摘要：当聚合物玻璃变形时，即使在样品温度没有明显变化的情况下，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，迁移率的变化是聚合物玻璃的非线性机械响应的原因。在变形过程中，系统在势能地貌上的位置可以改变。了解这些变化是这项工作的中心目标，因为这对于提高对聚合物玻璃变形的理解至关重要。将同时使用恒应变率和恒应力变形。恒定应变率实验提供了受控的屈服通道，从而允许在系统拉起能量图景时观察分子流动性的变化。压力老化实验被解释为系统被拉下了能量版图；压力老化期间的迁移率测量将检验这一解释。实验结果与模拟和模型预测的比较应该会增加对玻璃变形的基本理解和更好的预测能力。非技术综述：聚合物玻璃在我们的社会中被广泛使用。这些材料每天都可以看到防弹玻璃、光盘、安全玻璃和汽车前灯盖。在波音787等下一代商用飞机中，机翼和机身将由聚合物玻璃(与其他材料复合)制成。在这种应用中，聚合物玻璃之所以被使用，是因为它们能够在压力下变形而不破裂。通过增加我们对聚合物玻璃变形的基本了解，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。更准确的预测反过来将导致这些材料在交通等领域的进一步应用，在这些领域，轻质材料可以节省能源，从而有助于减少温室气体排放。每年，这些研究人员将为15名高中生举办为期三周的暑期丰富课程，他们中的大多数将来自科学和工程领域代表性较低的群体。这些研究人员每天花两个小时提供活动，旨在提高人们对科学/工程的兴趣，并培养在大学取得成功所需的关键技能。

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.