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

非技术总结：聚合物玻璃（用于汽车前照灯罩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，并且制造时需要很少的能量。聚合物玻璃对外力（拉伸与断裂）的响应决定了哪些材料可以用于特定的应用，但这种响应目前还无法预测。实验将用于测量当一个力施加在聚合物玻璃上时聚合物分子运动的速率；特别是，将利用玻璃周期性受压和非受压的实验。通过与模型和计算机计算的比较，这些实验将导致对聚合物玻璃力学性能的更可靠预测的发展。这可能会通过允许更广泛地利用这些轻质材料而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PEOPLE项目合作，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这项研究，并利用他们的经验指导高中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，针对高中生具有挑战性的概念。技术概述：聚合物玻璃由于其低密度、低成型所需的能量输入和有用的机械性能而在技术上具有重要意义。本研究旨在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；这将导致开发更可靠的模型来预测聚合物玻璃的机械性能。将在机械变形之前、过程中和之后测量聚甲基丙烯酸甲酯和聚乳酸玻璃中的片段迁移率。片段迁移率将通过光学光漂白方法测量，该方法提供了稀释探针分子集合的旋转相关函数。增强的迁移率是聚合物玻璃对变形非线性响应的一个关键特征。这些实验将利用循环拉伸加载/卸载变形和更复杂的变形协议。这些实验将区别于所有定性解释恒定应变速率下变形的理论模型。此外，本工作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。该项目支持的人员将与威斯康星大学麦迪逊分校的PEOPLE项目合作，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这项研究，并利用他们的经验指导高中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，针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.