NIRT: Influence of Nanoscale Structure and Dynamics on the Deformation of Polymer Glass Nanocomposites

尽管聚合物玻璃是令人印象深刻的工程材料，但仍有相当大的机会来提高其强度和破坏性能。最近的证据表明，用纳米级颗粒（即纳米复合材料）增强聚合物玻璃可以生产出强度和破坏性能大大提高的材料，并且根据目前的理解，无法以任何其他方式生产。新型玻璃纳米复合材料的系统开发将需要对纳米尺度上的变形过程有一个复杂的理解。我们建议综合运用实验、模拟和理论来发展所需的理解。实验将用于表征模型PMMA/二氧化硅纳米复合材料的宏观和微观变形行为。变形引起的聚合物迁移率将首次在这些材料中被量化。实验结果将与连续体、中尺度和微观理论方法进行比较。计算机模拟将指导和检查理论发展。要解决的关键问题包括：聚合物玻璃的内在纳米尺度非均质性与纳米颗粒的存在之间的相互作用是什么？对于多大尺寸的纳米颗粒，聚合物玻璃的连续模型不能描述实验行为？变形引起的流动性的微观起源是什么？纤维内部的动力是什么？聚合物玻璃的力学非均质性和动力学非均质性之间的关系是什么？拟议工作的计算需求是巨大的，我们将充分利用新兴的国家网络基础设施，包括美国国家科学基金会支持的威斯康星州网格实验室（GLOW）。我们预计这项工作将至少在两个方面产生广泛的影响。新型聚合物玻璃纳米复合材料迫切需要解决令人烦恼的制造问题，如先进光刻技术造成的纳米级光刻胶特性的弱点。我们的主要技术目标是开发工具，使用最小的实验输入，可以预测玻璃纳米复合材料的变形特性，作为温度，热历史，应变速率和变形几何的函数。此外，pi将与威斯康辛大学麦迪逊分校的一个名为PEOPLE的项目合作，以增加少数民族和低收入高中学生进入学院和大学的可能性。pi和我们的同事将提供经验，帮助这些学生成为具有科学素养的公民，并鼓励他们考虑从事科学和工程方面的职业；我们将与这些学生的老师在我们的实验室和教学材料的开发工作。PEOPLE项目在将90%以上的参与者送入大学方面有着良好的记录。

ABSTRACT - 0506840U of Wisconsin MadisonEven though polymeric glasses are impressive engineering materials, there are considerable opportunities to improve their strength and failure properties. Recent evidence indicates that reinforcement of polymer glasses with nanoscale particles (i.e. nanocomposites) can produce materials with strength and failure properties that are substantially improved and, given current understanding, cannot be produced in any other manner. The systematic development of new glassy nanocomposites will require an intricate understanding of deformation processes on the nanoscale. We propose an integrated effort that utilizes experiments, simulations, and theory to develop the needed understanding. Experiments will be used to characterize both the macroscopic and microscopic deformation behavior of model PMMA/silica nanocomposites. Deformation-induced polymer mobility will be quantified for the first time in these materials. Experimental results will be compared with continuum, mesoscale, and microscopic theoretical approaches. Computer simulations will guide and check the theoretical developments. Key questions to be addressed include: What is the interaction between the intrinsic nanoscale heterogeneity of a polymer glass and the presence of a nanoparticle? For what size nanoparticles do continuum models of the polymer glass fail to describe the experimental behavior? What is the microscopic origin of deformation-induced mobility? What are the dynamics inside a fibril created by crazing? What is the relationship between mechanical and dynamic heterogeneity in polymer glasses? The computational demands of the proposed work are substantial and we will take full advantage of the emerging national cyber infrastructure, including the NSF supported Grid Laboratory of Wisconsin (GLOW). We anticipate that this work will have broad impact in at least two dimensions. New polymer glass nanocomposites are urgently needed to solve vexing manufacturing problems such as the weakness of nanoscale photoresist features created by advanced lithography. Our primary technical goal is to develop tools that, using a minimum of experimental input, can predict the deformation properties of glassy nanocomposites as a function of temperature, thermal history, strain rate, and deformation geometry. Additionally, the PIs will work with a University of Wisconsin-Madison program known as PEOPLE (Pre-college Enrichment Opportunity Program for Learning Excellence) to increase the likelihood that minority and low-income high school students matriculate to colleges and universities. The PIs and our coworkers will provide experiences that will help these students to become scientifically literate citizens and encourage them to consider careers in science and engineering; we will work with teachers of these students in our laboratories and in the development of instructional materials. The PEOPLE program has a proven track record of sending more than 90% of its participants to college.