Influence of Cyclic Loading/Unloading on Segmental Dynamics of Polymer Glasses

非技术总结：聚合物玻璃（用于汽车前照灯盖和现代复合材料飞机等应用的材料）在技术上很重要，因为它们坚硬，重量轻，制造所需的能源很少。聚合物玻璃对外力的响应（拉伸与断裂）决定了哪些材料可用于特定应用，但目前无法预测这种响应。实验将被用来测量聚合物分子运动发生的速率时，力施加到聚合物玻璃;特别是，实验中，玻璃周期性地强调和无应力将被利用。通过与模型和计算机计算的比较，这些实验将导致更可靠的预测聚合物玻璃的机械性能的发展。通过允许更广泛地利用这些轻质材料，这可能会产生重大的经济影响。该项目支持的人员将与威斯康星大学麦迪逊分校的人民计划合作，为来自代表性不足群体的高中生上大学做准备。两名高中科学教师将参与研究，并利用他们的经验指导高中学生进行独立的研究项目。这些教师还将开发用于威斯康星州公立高中的模块，这些模块针对高中生具有挑战性的概念。技术总结：聚合物玻璃由于其低密度，成型所需的低能量输入以及其有用的机械性能而在技术上很重要。 这项研究的目的是提高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，这将导致更可靠的模型的发展，用于预测聚合物玻璃的机械性能。将在机械变形之前、期间和之后测量聚（甲基丙烯酸甲酯）和聚（乳酸）玻璃中的节段流动性。分段流动性将测量与光学光漂白方法，提供访问的旋转相关函数的一个系综的稀释探针分子。 增强的迁移率是聚合物玻璃对变形的非线性响应的关键特征。这些实验将利用循环拉伸加载/卸载变形和更复杂的变形方案。这些实验将区分所有定性解释恒定应变速率下变形的理论模型。此外，这项工作将通过材料研究和教育活动的结合，促进研究生和高中生的培训。 该项目支持的人员将与威斯康星大学麦迪逊分校的人民计划合作，为来自代表性不足群体的高中生上大学做准备。两名高中科学教师将参与研究，并利用他们的经验指导高中学生进行独立的研究项目。这些教师还将开发用于威斯康星州公立高中的模块，这些模块的目标是对高中生具有挑战性的概念。

Non-Technical Summary: Polymer glasses (materials used in applications like automobile headlamp covers and modern composite aircraft) are important in technology because they are stiff, lightweight, and require little energy for manufacture. The response of polymer glasses to external forces (stretching vs. breaking) determines what materials can be used for particular applications but this response currently cannot be predicted. Experiments will be used to measure the rate at which polymer molecular motions occur when a force is applied to the polymer glass; in particular, experiments in which the glass is periodically stressed and unstressed will be utilized. Through comparison with models and computer calculations, these experiments will lead to the development of more reliable predictions of the mechanical properties of polymer glasses. Potentially this will have a significant economic impact by allowing broader utilization of these lightweight materials. Personnel supported by this project will work with the University of Wisconsin-Madison's PEOPLE program to prepare high-school students from under-represented groups for college. Two high-school science teachers will participate in the research and use their experience to guide high-school students in independent research projects. These teachers will also develop modules for use in Wisconsin public high schools that target concepts which are challenging for high-school students.Technical Summary: Polymer glasses are important in technology due to their low density, the low energy input required for molding, and their useful mechanical properties. This research aims to enhance the fundamental understanding of polymer glass deformation and to test current theoretical approaches and computer simulations; this should lead to the development of more reliable models for the prediction of the mechanical properties of polymer glasses. Segmental mobility in poly(methyl methacrylate) and poly(lactic acid) glasses will be measured before, during, and after mechanical deformation. Segmental mobility will be measured with an optical photobleaching method that provides access to the rotational correlation function of an ensemble of dilute probe molecules. Enhanced mobility is a key feature of the nonlinear response of polymer glasses to deformation. These experiments will utilize cyclic tensile loading/unloading deformations and more complex deformation protocols. These experiments will discriminate among theoretical models that all qualitatively explain deformation at constant strain rate. In addition, this work will advance the training of graduate students and high-school students, through the integration of materials research and education activities. Personnel supported by this project will work with the University of Wisconsin-Madison's PEOPLE program to prepare high-school students from under-represented groups for college. Two high-school science teachers will participate in the research and use their experience to guide high-school students in independent research projects. These teachers will also develop modules for use in Wisconsin public high schools that target concepts which are challenging for high-school students.