Thermodynamic and Dynamic Behaviour in Polymer Melts, Glasses, and Mixtures: Links to Structure Using Theory and Simulation

该奖项支持聚合物系统和相关材料的理论和计算研究和教育。合成材料如聚合物有许多应用，从电子涂料到服装、家具和飞机部件。理想情况下，材料性能将很好地匹配预期用途：例如，硬壳行李箱的韧性和耐磨性，垃圾袋的抗撕裂性。新的合成策略产生了令人印象深刻的能力，可以设计一个大分子，使其原子被结合在一起，以及它们如何在局部连接。在这个项目中，PI和她的团队将使用理论和模拟来开发新的工具来预测分子组成如何控制大块材料的特性。由于许多应用都涉及到薄膜，因此界面的影响也将引起人们的强烈兴趣。贯穿许多拟议研究的重要主题之一涉及在固体或液体中捕获的“未使用”体积；它会随着压强和温度的变化而变化。例如，液体的密度会随着温度的降低而增大；固体玻璃态的“自由”体积比液体小。PI小组先前的研究表明，对自由体积的理论预测与材料特性有关，例如其熔化温度、吸收能量的方式以及混合的倾向。这项工作将集中在连接自由体积和分子结构。其目的是完成连接大分子的微观设计与其体积和薄膜性质的路径。这一过程将为科学界的材料设计引入新的策略。所有参与研究的本科生和博士后的教育和培训将是广泛的，因为PI的研究强调的是让模拟和理论直接对实验结果负责。PI在让女性参与研究方面有着良好的记录，也对公众宣传保持着兴趣。该奖项支持理论研究和教育，旨在发现聚合物熔体、混合物和玻璃中的结构、平衡性质和动态响应之间的联系，以及通过界面的限制。合成专家正在开发能够增加对分子含量控制的方法，在化学成分和行为之间划出清晰界限的能力至关重要。这里感兴趣的材料包括熔体和溶液中的大分子，以及玻璃状固体。分析理论和模拟都将被引入，这两条路线将在一些感兴趣的研究中重叠。这项研究将产生可验证的预测，这些预测将对实验数据负责。结果将是选择分子成分以产生所需物理性质的新策略。研究目标包括：(1)热力学表征与动态响应之间的联系。初步证据表明，在先前的NSF支持下开发的局部相关晶格（LCL）模型产生了一个定义良好的自由体积热力学量化。此外，自由体积预测与玻璃化转变相关，并为聚合物和小分子体系中动态弛豫的温度和体积依赖性提供了解释。PI的目标是利用跨越数十年的弛豫数据以及广泛的温度和压力范围，将这些结果扩展到各种聚合物和其他玻璃体系。使用LCL自由体积的热力学缩放将把每个系统的整个数据集压缩到一条线上，只需要一个优化参数。应用于许多系统将允许局部化学结构之间的关联，可以综合控制，和材料依赖的缩放参数。结果将是预测设计结构如何动态松弛的能力。标度分析也将导致仅给定环境压力实验数据的动态松弛的压力依赖性的预测。体和薄膜系统都将被研究。(2)自由体积和内聚能密度对混相的正交控制。内聚能密度在预测聚合物溶液和共混物的混相方面一直表现不佳。应用LCL模型研究混合行为表明LCL自由体积与内聚能密度是一个正交度量；有证据表明，当内聚能密度失效时，它可以作为一种预测工具。LCL理论可以预测这两个量，这将使这个假设得到验证。应用于许多系统将允许与分子性质的相关性，特别感兴趣的是链刚度。(3)研究界面影响的粗粒度模拟方法。界面的引入和控制在材料设计中起着越来越重要的作用。PI的有限移动模拟方法可以模拟一系列实验观察到的行为。关键特征包括局部密度和局部流动性之间的解耦，以及为局部移动提供最近邻便利。初步结果表明，模拟参数值与实验测量的分子特性密切相关。在这项工作中，有限迁移率模型将被应用于捕捉各种界面的破坏性影响，包括抗/塑化添加剂和多层系统。

NONTECHNICAL SUMMARYThis award supports theoretical and computational research and education on polymeric systems and related materials. There are many applications for synthetic materials such as polymers, ranging from coatings for electronics, to clothing, furniture, and airplane components. Ideally, the material properties will be well matched to the intended use: e.g. tough and abrasion-resistant for hard-shell suitcases, resistant to tear for garbage bags. New synthetic strategies are yielding impressive ability to design a large molecule down to the level of which atoms are incorporated and how they are locally connected. In this project, the PI and her group will use theory and simulation to develop new tools for predicting how molecular composition controls bulk material properties. Because so many applications involve thin films, the effects of interfaces will also be of strong interest. One of the important themes that runs through much of the proposed research involves the "unused" volume captured within a solid or liquid; this will change with pressure and temperature. For example, a liquid will become more dense as temperature is lowered; a solid glassy state has less "free" volume than the liquid. Prior research in the PI's group shows that theoretical predictions for free volume correlate with materials properties, e.g. its melting temperature, how it absorbs energy, and its tendency to mix. This work will focus on linking free volume and molecular structure. The aim is to complete the path connecting the microscopic design of large molecules to their bulk and film properties. The process will introduce new strategies to the scientific community for materials design. Education and training of all undergraduate students and postdocs involved in the research will be broad since a strong emphasis in the PI's research is to hold simulation and theory directly accountable to experimental results. The PI has a strong track record of involving women in research, and also maintains an interest in public outreach.TECHNICAL SUMMARYThis award supports theoretical research and education aimed at discovering links between structure, equilibrium properties, and dynamic response in polymer melts, mixtures and glasses, in the bulk and confined through interfaces. Synthesis experts are developing methods that allow for increasing control of molecular content, and the ability to draw bright lines between chemical constituency and behavior is crucial. Materials of interest here include macromolecules in melt and solution, and glassy solids. Both analytic theory as well as simulations will be brought to bear, and the two routes will overlap for some of the studies of interest. The research will generate testable predictions that will be held accountable to experimental data. The result will be new strategies for choosing molecular constituents so as to produce desired physical properties. The goals of research include: (1) Connections between thermodynamic characterization and dynamic response. Preliminary evidence shows that the Locally Correlated Lattice (LCL) model developed under prior NSF support yields a well-defined thermodynamic quantification of free volume. Further, the free volume predictions correlate with the glass transition, and suggest an explanation for the temperature and volume dependence of dynamic relaxation in polymeric and small molecule systems. The PI aims to extend these results to a large variety of polymeric and other glassy systems, using relaxation data that spans many decades, as well as a broad range of temperatures and pressures. Thermodynamic scaling using the LCL free volume will collapse the entire data set for each system to a single line, requiring only a single optimization parameter. Application to many systems will allow correlation between local chemical structure, which can be synthetically controlled, and the material dependent scaling parameter. The result will be an ability to predict how a designed structure will dynamically relax. The scaling analysis will also lead to predictions about the pressure dependence of dynamic relaxation, given only ambient pressure experimental data. Both bulk and thin film systems will be studied.(2) Free Volume and Cohesive Energy Density as Orthogonal Controls on Miscibility. The cohesive energy density has a poor history of predicting miscibility in polymer solutions and blends. Application of the LCL model to study mixing behavior has shown the LCL free volume to be an orthogonal metric to cohesive energy density; there is evidence that it can serve as a predictive tool where the cohesive energy density fails. The LCL theory can predict both quantities, which will allow this hypothesis to be tested. Application to many systems will allow correlations with molecular properties, a particular interest being chain stiffness. (3) A Coarse-grained Simulation Method for Studying the Effects of Interfaces. Introduction and control of interfaces plays an increasingly important role in material design. The PI's Limited Mobility simulation approach can model a range of experimentally observed behavior. Key features include decoupling between local density and local mobility, and incorporating nearest-neighbor facilitation for local moves. Initial results indicate that simulation parameter values connect closely with experimentally measured characteristic molecular properties. In this work, the limited mobility model will be applied to capture the disruptive influences of a wide variety of interfaces, including anti/plasticizing additives and multilayer systems.