Deformation-induced changes in segmental dynamics of polymer glasses prepared by melt stretching and stress aging

熔融拉伸和应力老化制备的聚合物玻璃的变形引起的链段动力学变化

• 批准号: 2002959
• 负责人: Mark Ediger
• 金额: $ 47.05万
• 依托单位: University of Wisconsin-Madison
• 依托单位国家: 美国
• 项目类别: Standard Grant
• 财政年份: 2020
• 资助国家: 美国
• 起止时间: 2020-07-01 至 2024-06-30
• 项目状态: 已结题
• 来源: https://www.nsf.gov/awardsearch/showAward?AWD_ID=2002959&HistoricalAwards=false
• 关键词: Deformation; induced; changes; segmental; dynamics

NON-TECHNICAL SUMMARY:Polymer glasses are important materials due to their high transparency, the low energy input required for molding them into particular shapes, their stiffness, and their resistance to breakage. Polymer glasses are used in applications as diverse as advanced aircraft composites and eyeglass lenses. The planned research will investigate how polymer glasses respond when they are subjected to large forces. In particular, the experiments will use lasers and microscopes to measure how the polymer molecules rearrange when a polymer glass is deformed. Current theories and computer simulations have identified this molecular motion as a key quantity that must be understood to determine if a polymer glass will stretch, deform, or break. The polymer glasses to be used will be processed in special ways (stretched at high temperature or deformed at low temperature) to critically test these simulations and theories. The proposed experiments should lead to more reliable models for the prediction of the mechanical properties of polymer glasses. This in turn may have a significant economic impact because of the broad potential of these lightweight materials. The students involved in this project will learn how to characterize polymer glasses and improve the properties of materials. All personnel supported by this grant will participate in a program to increase the number of highly qualified students from underrepresented groups that enter Ph.D. programs in the U.S.TECHNICAL SUMMARY:The deformation properties of polymer glasses are extremely challenging to predict as a result of the nonlinear nature of the deformation and the nonequilibrium nature of the glass. Here it is proposed to measure segmental mobility in polymer glasses during deformation using an optical photobleaching method that provides access to the rotational correlation function of an ensemble of dilute probe molecules. Deformation can increase segmental mobility in polymer glasses by more than a factor of 1000, and an understanding of this enhanced mobility is a key requirement for accurate modeling of the mechanical properties of polymer glasses. For the proposed work, polymer glasses will be prepared by melt quenching so that subsequent mobility measurements during deformation can disentangle the influences of yield and strain hardening on segmental mobility. The proposed work will also test whether deformed polymer glasses can show indications of overaging, i.e., physical aging that occurs at an accelerated rate as a result of applied stress. Finally, the generality of the results obtained in tensile deformation will be tested by performing optical measurements of segmental mobility during shear deformation. The proposed experiments can provide a molecular-level test of theoretical descriptions of polymer glass deformation. The experimental results obtained, in comparison with theory and simulation, should lead to an enhanced fundamental understanding of the deformation of polymer glasses. All personnel supported by this grant will participate in a program to increase the number of highly qualified students from underrepresented groups that enter Ph.D. programs in the U.S..This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.

非技术概述：聚合物玻璃是重要的材料，因为它们具有高透明度，将它们模塑成特定形状所需的低能量输入，它们的刚度和抗破碎性。聚合物玻璃广泛应用于先进的飞机复合材料和光学镜片等领域。计划中的研究将研究聚合物玻璃在受到巨大作用力时的反应。特别是，实验将使用激光和显微镜来测量聚合物玻璃变形时聚合物分子的重排方式。目前的理论和计算机模拟已经将这种分子运动确定为一个关键量，必须理解它才能确定聚合物玻璃是否会拉伸、变形或破裂。将使用的聚合物玻璃将以特殊的方式进行处理（在高温下拉伸或在低温下变形），以严格测试这些模拟和理论。拟议的实验应导致更可靠的模型预测的聚合物玻璃的机械性能。 由于这些轻质材料的广泛潜力，这反过来可能会产生重大的经济影响。 参与该项目的学生将学习如何表征聚合物玻璃和改善材料的性能。所有由该补助金支持的人员将参加一项计划，以增加进入博士学位的代表性不足的群体的高素质学生的数量。技术概述：由于变形的非线性性质和玻璃的非平衡性质，预测聚合物玻璃的变形性质极具挑战性。在这里，它建议使用光学光漂白方法，提供访问的稀释探针分子的合奏的旋转相关函数的变形过程中测量聚合物玻璃中的链段迁移率。 变形可以增加聚合物玻璃中的链段流动性超过1000倍，并且对这种增强的流动性的理解是精确建模聚合物玻璃的机械性能的关键要求。对于所提出的工作，聚合物玻璃将通过熔融淬火制备，以便在变形过程中随后的流动性测量可以解开屈服和应变硬化对分段流动性的影响。拟议的工作还将测试变形的聚合物玻璃是否可以显示出过度老化的迹象，即，由于施加应力而加速发生的物理老化。 最后，在拉伸变形中获得的结果的一般性将通过在剪切变形过程中进行节段流动性的光学测量进行测试。实验结果为聚合物玻璃变形的理论描述提供了分子水平的检验。所获得的实验结果，与理论和模拟相比，应导致增强的聚合物玻璃的变形的基本理解。所有由该补助金支持的人员将参加一项计划，以增加进入博士学位的代表性不足的群体的高素质学生的数量。在美国的节目。该奖项反映了NSF的法定使命，并被认为是值得通过使用基金会的知识价值和更广泛的影响审查标准进行评估的支持。

项目成果

Segmental Dynamics in the Strain-Hardening Regime for Poly(methyl methacrylate) Glasses with and without Melt Stretching

• DOI: 10.1021/acs.macromol.2c01442
• 发表时间: 2022-09
• 期刊: Macromolecules
• 影响因子: 5.5
• 作者: Enran Xing;Trevor Bennin;M. Razavi;M. Ediger

Overaging with Stress in Polymer Glasses? Faster Segmental Dynamics despite Larger Yield Stress!

• DOI: 10.1021/acs.macromol.2c01338
• 发表时间: 2022-11
• 期刊: Macromolecules
• 影响因子: 5.5
• 作者: M. Razavi;Enran Xing;M. Ediger

Rejuvenation Versus Overaging: The Effect of Cyclic Loading/Unloading on the Segmental Dynamics of Poly(methyl methacrylate) Glasses

• DOI: 10.1021/acs.macromol.0c01489
• 发表时间: 2020-09
• 期刊: Macromolecules
• 影响因子: 5.5
• 作者: Trevor Bennin;Enran Xing;J. Ricci;M. Ediger

Multistep Deformation Experiment and Development of a Model for the Mechanical Behavior of Polymeric Glasses

• DOI: 10.1021/acs.macromol.2c00711
• 发表时间: 2022-07
• 期刊: Macromolecules
• 影响因子: 5.5
• 作者: G. Medvedev;Enran Xing;M. Ediger;J. Caruthers