Collaborative Research: Spatial and Dynamic Heterogeneity and Nonlinear Viscoelastic Constitutive Behavior of Glasses and Their Nanocomposites as Probed by Nonlinear Spectroscopies

该研究项目将回答与玻璃聚合物及其纳米复合材料性能相关的基本问题。这些材料对于广泛的国防和商业应用非常重要。两种机械光谱技术将用于识别这些材料的独特“指纹”。虽然通常用于软质材料，但本研究将采用这种方法来研究玻璃聚合物及其纳米复合材料的非线性响应。该研究将实验与计算相结合，以推进这些先进材料的科学和工程基础。两所大学的外展项目为K-12学生和教师提供了机会，通过探索工程、材料和回收利用的活动，提高他们对STEM的理解和熟悉程度。来自代表性不足群体的学生将被招募到工作的所有活动中。将通过出版成果和在主要会议上对工作进行技术性介绍以及将研究结果纳入课程来扩大其影响。该研究的具体目标是利用纳米颗粒增强聚合物玻璃来阐明不同长度尺度和非均质性对聚合物玻璃及其纳米复合材料的非线性粘弹性的影响。研究的丰富性源于这样一个事实，即在包括聚合物在内的玻璃形成系统中，人们一致认为非均质性在几纳米尺度上，而在纳米复合材料中，感兴趣的尺寸范围可以从聚合物的非均质尺度变化到多个颗粒的尺寸，即100纳米以上。有重要的证据表明，聚合物基体本身的性质受到界面和约束效应的改变，从而导致这些材料具有丰富的非均质性。本研究利用机械光谱烧孔（MSHB）和大振幅振荡剪切（LAOS）指纹图谱框架，阐明了不同尺度和非均质性对聚合物玻璃及其纳米复合材料非线性粘弹性的影响，这是迄今为止尚未研究的问题。其目的是系统地改变异质性的规模和性质，通过实验来识别它，并将结果与行为的计算模型进行比较。结果将大大提高对玻璃聚合物及其纳米复合材料的非均质性如何影响非线性行为和性能的理解。该奖项反映了美国国家科学基金会的法定使命，并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，被认为值得支持。

This research project will answer fundamental questions related to the performance of glassy polymers and their nanocomposites. These materials are important for a wide range of defense and commercial applications. Two mechanical spectroscopy techniques will be used to identify the unique “fingerprint” of these materials. Although normally used for soft materials, this research will employ this approach to investigate the nonlinear response of glassy polymers and their nanocomposites. The study combines experiment and computation to advance the science and engineering fundamentals of these advanced materials. The outreach programs at both universities provide opportunities for K-12 students and teachers to advance in their understanding and familiarity with STEM through activities exploring engineering, materials, and recycling. Students from underrepresented groups will be recruited to all activities of the work. The impact will be broadened by publication of results as well as technical presentation of the work at major conferences and incorporation of the findings in courses.The specific goals of the research are to use nanoparticle reinforced polymer glasses to elucidate the impact of different length scales and heterogeneity on the nonlinear viscoelasticity of polymer glasses and, simultaneously, their nanocomposites. The richness of the study arises from the facts that, in glass-forming systems including polymers, there is a consensus that the heterogeneities are on the scale of a few nanometers whereas in nanocomposites the size-scale range of interest can vary from that of the heterogeneity-scale of the polymer to the size of multiple particles, i.e., above 100 nm. There is significant evidence that properties of the polymer matrix itself are modified by the interphases and confinement effects, thus leading to a rich range of heterogeneity in these materials. The work uses the mechanical spectral hole burning (MSHB) and large amplitude oscillatory shear (LAOS) fingerprinting framework to elucidate the impact of different scales and heterogeneity on the nonlinear viscoelasticity of polymer glasses and their nanocomposites, something that has heretofore not been investigated. The intent is to systematically vary the scale and nature of the heterogeneity, to fingerprint it experimentally, and compare the results with computational models of behavior. The outcome will be a greatly improved understanding of how heterogeneity in glassy polymers and their nanocomposites impacts nonlinear behavior and, consequently, performance.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.