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，应用范围广泛，包括传感器、可穿戴电子设备和生物医学应用。然而，这些材料经常存在机械强度低的问题，特别是在高温下。在极端条件下具有高强度的软杂化材料已经在小范围内开发出来，但要将这些材料扩大到制造能力，必须了解控制这些材料力学行为的基本机制。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潜在物理和化学因素。这项研究产生的科学知识有可能创造出一类新的高性能材料，而实验和计算相结合的方法建立在为学生提供参与研究的机会的教育范式之上，培训下一代劳动力掌握先进的工程技术。这项研究的一个驱动力是基于纳米复合材料独特的动态行为开发机械适应材料。感兴趣的材料体系由玻璃化转变温度(Tg)相差很大的可混溶聚合物和分散的纳米颗粒组成。球形纳米颗粒吸附在高玻璃化温度的聚合物中并分散在低玻璃化温度的聚合物基质中，已被证明导致了热诱导硬化行为。在这项研究计划中，研究人员考察了化学和动态异质性在此类聚合物纳米复合材料的颗粒-聚合物界面中的作用，以了解适应性的力学特征。为了解释不同聚合物结构和不同颗粒形状(纳米管和纳米球)中的增强现象，研究了界面聚合物层中的化学不均一性。将通过分子动力学计算模拟来探索处于环状、拉伸和塌陷状态的链的构象，以支持实验结果。计算机模拟被设计为与实验并行运行，以指导实验工作并为材料设计空间提供信息。更重要的是，通过这些模拟可以识别各种分子物理参数的影响，如链的刚性。利用聚合物纳米复合材料在大振动剪切下的变形来揭示复合材料中自适应力学的基本机理。现有的网络理论将用于分析非线性流变数据以及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转变目前关于纳米复合材料静态性能的知识，扩展到动态自适应聚合物杂交体。该奖项反映了NSF的法定使命，并通过使用基金会的智力优势和更广泛的影响审查标准进行评估，被认为值得支持。

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.