CAREER: Understanding the Multi-Scale Dynamics of Heterogeneous Polymeric Systems

第1部分：非技术概述：新兴的聚合物加工方法，如3D打印和压印光刻，通常需要具有非常规流变或流动特性的材料。聚合物在液体和固体状态下的这些特性是由短长度尺度（约10个分子键，~1纳米）和长长度尺度（数百个分子键，~10纳米）上的分子运动关系决定的。该项目旨在了解这些多尺度聚合物动力学，利用聚合物和超小（~2纳米）纳米颗粒之间的可调相互作用作为模型系统。本研究获得的基本认识将指导材料设计以揭示非常规流动特性。此外，新发展的荧光技术将用于高通量聚合物体系的多尺度动力学研究。该研究与聚合物纳米复合材料市场相关，预计2019年全球市场规模为41亿美元，预计到2024年将达到85亿美元。教育计划与研究计划相结合，以激励下一代的规划师、科学家和工程师。外展和指导活动将扩大参与，并将通过示范和实验室实习培养来自低收入社区的K-12学生对聚合物的迷恋和兴趣。一门针对大四本科生和研究生的新课程将通过尖端的荧光技术将高分子/材料科学与生命科学联系起来，并强调有效的科学交流。第2部分：技术概述聚合物的段和链动力学之间的关系决定了玻璃和熔体的性能，对设计加工操作至关重要。然而，尽管在过去六十年中取得了很大进展，但这种跨时间和长度尺度关系的物理基础仍然难以捉摸，尽管很明显，动态异质性是关键贡献。由于空间异质性难以控制，以及缺乏高通量实验技术来研究节段和全链动力学，理解非均质节段摩擦影响的尝试受到限制。为此，本项目旨在阐明非均质节段摩擦对全链运动从节段动力学解耦的影响，即偏离理想均质聚合物的节段运动和全链运动之间的预测关系。为了建立一个可控的非均相系统，PI的团队正在开发聚合物纳米复合材料，其中所有的链都有效地与分散良好的、非常小的纳米颗粒相连接，这些纳米颗粒的大小与片段相当。目的1和2将揭示聚合物-纳米颗粒相互作用和分子量在多尺度动力学上的相互作用。在Aim 3中，新发展的荧光技术将被用于高效地研究聚合物体系的多尺度动力学。将实验数据与非均相劳斯模型等模型进行比较，将为非均相聚合物体系中节段全链运动的解耦提供新的见解。预计这种解耦将允许通过添加超小纳米颗粒或设计具有最佳单体序列的聚合物来改变流变特性。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。

PART 1: NON-TECHNICAL SUMMARY:Emerging polymer processing methods, such as 3D printing and imprint lithography, often require materials with unconventional rheological, or flow, properties. Such properties in liquid and solid states of polymers are dictated by the relationship between molecular motion on short length scales (about ten molecular bonds, ~1 nanometer) and molecular motion on long length scales (hundreds of molecular bonds, ~10 nanometers). This project aims to understand these multi-scale polymer dynamics, leveraging tunable interactions between polymers and ultrasmall (~2 nanometers) nanoparticles as a model system. The fundamental understanding obtained in this study will guide materials designs to reveal unconventional flow properties. Moreover, newly developing fluorescence technologies will be employed to study multi-scale dynamics of polymer systems with high throughput. This research is relevant in the polymer nanocomposites market, estimated to be $4.1 billion worldwide in 2019, and predicted to reach $8.5 billion by 2024. The educational plan is integrated with the research plan to inspire the next generation of planners, scientists, and engineers. The outreach and mentoring activities will broaden participation and will cultivate fascination and interest in polymers among K-12 students from low-income communities through demonstrations and laboratory internships. A proposed new course for senior undergraduates and graduate students will bridge polymer/materials science to life sciences through cutting-edge fluorescence technologies with an emphasis on effective science communication. PART 2: TECHNICAL SUMMARYThe relationship between segmental and chain dynamics of polymers dictates both glass and melt properties and is crucial to designing processing operations. However, the physical foundations of this relationship across multiple time and length scales remain elusive despite much progress over the past sixty years, although it is clear that dynamic heterogeneities are the key contribution. Attempts to understand the influence of heterogeneous segmental friction are limited by the difficulty to control spatial heterogeneity, and a lack of high-throughput experimental techniques for studying segmental and entire chain dynamics. To this end, this project aims to elucidate the influence of heterogeneous segmental friction on the decoupling of entire chain motion from segmental dynamics, i.e., deviations from the predicted relationships between segmental and entire chain motion for ideal homogenous polymers. To establish a controlled heterogeneous system, the PI's group is developing polymer nanocomposites in which all chains are effectively interfacial with well dispersed, very small nanoparticles that are comparable in size to segments. Aims 1 and 2 will uncover the interplay of polymer-nanoparticle interactions and molecular weight on multi-scale dynamics. In Aim 3, newly developing fluorescence technologies will be employed to study multi-scale dynamics of polymer systems efficiently. A comparison of experimental data to models such as the Heterogeneous Rouse Model will provide new insight into the decoupling of segmental entire chain motion in heterogeneous polymeric systems. It is anticipated that such decoupling will allow rheological properties to be altered simply by adding ultra-small nanoparticles or by designing polymers with optimal monomer sequences..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.