Collaborative Research: Chemical and Dynamic Heterogeneities in Interfaces for Adaptive Polymer Nanocomposites

聚合物复合材料被广泛用作轻质功能材料，用于广泛的应用，包括传感器，可穿戴电子产品和生物医学应用。然而，这些材料通常具有低的机械强度，特别是在高温下。在极端条件下具有高强度的软混合材料已经在小规模上开发出来，但是为了将这些材料扩大到制造能力，必须理解控制这些材料的机械行为的基本机制。该奖项支持基础研究，以揭示控制自适应聚合物纳米复合材料的高机械和功能性能的基础物理和化学。从这项研究中获得的科学知识有可能使一类新的高性能材料成为可能，实验和计算相结合的方法建立在一种教育范式的基础上，为参与研究的学生提供机会，培养下一代先进工程技术的劳动力。这项研究的一个驱动动机是开发基于独特动力学的机械自适应材料，纳米复合材料的性能。感兴趣的材料系统由玻璃化转变温度（Tg）差异较大的可混溶聚合物组成，再加上纳米颗粒的分散体。吸附在高Tg聚合物内并分散在低Tg聚合物基质中的球形纳米颗粒已被证明导致热诱导硬化行为。在这项研究计划中，研究人员研究了化学和动态不均匀性在这种聚合物纳米复合材料的颗粒-聚合物界面中的作用，以了解适应性的机械特性。研究了界面聚合物层中的化学非均匀性，以解释不同聚合物结构和不同颗粒形状（纳米管和纳米球）的增强现象。构象的链，在循环，拉伸和塌陷状态，将探讨通过分子动力学计算模拟，以支持实验结果。计算机模拟设计与实验并行运行，以指导实验工作并告知材料设计空间。更重要的是，各种分子的物理参数，如链刚度的影响，可以确定这些模拟。 高分子纳米复合材料在大振动剪切下的变形将被用来揭示复合材料自适应力学的基本机制。现有的网络理论将用于分析非线性流变数据和不同聚合物结构对颗粒行为的影响。从这个项目中获得的知识将改变目前的纳米复合材料的静态性能的知识，扩展到动态自适应聚合物hybrids.This奖项反映了NSF的法定使命，并已被认为是值得通过使用基金会的智力价值和更广泛的影响审查标准进行评估的支持。

Polymer composites are widely used as lightweight functional materials for a breadth of applications, including sensors, wearable electronics, and biomedical applications. These materials, however, often suffer from low mechanical strength, particularly at elevated temperatures. Soft hybrid materials with high strength under extreme conditions have been developed at small scales, but to scale these materials up to manufacturing capacities, the fundamental mechanisms of controlling the mechanical behavior of these materials must be understood. This award supports fundamental research to uncover the underlying physics and chemistry that control the high mechanical and functional performance of adaptive polymer nanocomposites. The scientific knowledge resulting from this research has the potential to enable a new class of high-performance materials, and the combined experimental and computational approaches build on an educational paradigm that provides opportunities for students participating in the research, training the next generation workforce in advanced engineering techniques.A driving motivation of this research is to develop mechanically adaptive materials based on the unique dynamic behavior of nanocomposites. The material system of interest consists of miscible polymers with large differences in glass transition temperature (Tg), coupled with a dispersion of nanoparticles. Spherical nanoparticles adsorbed within a high-Tg polymer and dispersed in a low-Tg polymer matrix have been shown to result in a thermally-induced stiffening behavior. In this research program, the investigators examine the role of chemical and dynamic heterogeneities in particle-polymer interfaces of such polymer nanocomposites to understand the mechanical characteristics of adaptivity. Chemical heterogeneities in interfacial polymer layer are studied to explain the reinforcement phenomena in different polymer architectures and with different particle shapes (nanotubes and nanospheres). Conformation of chains, in looped, stretched, and collapsed states, will be explored via molecular dynamic computational simulations to support the experimental results. Computer simulations are designed to run in parallel with experiments to guide experimental work and to inform material design space. More importantly, the influence of various molecular physical parameters such as chain stiffness can be identified by these simulations. Deformation of polymer nanocomposites under large oscillatory shear will be utilized to reveal the fundamental mechanism of adaptive mechanics in composites. Existing network theories will be used to analyze the non-linear rheological data and the effects of different polymer architectures on particle behavior. The knowledge gained from this project will transform the current knowledge of static properties of nanocomposites to extend to dynamically adaptive polymer hybrids.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.