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

第一部分：非技术总结：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性质由短长度尺度（约10个分子键，~1纳米）上的分子运动和长长度尺度（数百个分子键，~10纳米）上的分子运动之间的关系决定。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。在这项研究中获得的基本理解将指导材料设计，以揭示非常规的流动特性。此外，新发展的荧光技术将被用于高通量研究聚合物系统的多尺度动力学。这项研究与聚合物纳米复合材料市场相关，2019年全球市场估计为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，以激励下一代规划师，科学家和工程师。推广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学生对聚合物的兴趣和兴趣。为高年级本科生和研究生提出的新课程将通过尖端荧光技术将聚合物/材料科学与生命科学联系起来，重点是有效的科学交流。第二部分：聚合物的链段和链动力学之间的关系决定了玻璃和熔体性质，对设计加工操作至关重要。然而，尽管在过去60年中取得了很大进展，但这种关系在多个时间和长度尺度上的物理基础仍然难以捉摸，尽管动态异质性显然是关键贡献。试图了解异质性链段摩擦的影响是有限的，难以控制空间异质性，并缺乏高通量的实验技术，研究链段和整个链的动态。为此，本项目旨在阐明非均匀链段摩擦对整个链运动与链段动力学解耦的影响，即，与理想均相聚合物的链段和整个链运动之间的预测关系的偏差。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，其中所有链都有效地与分散良好的非常小的纳米颗粒界面，这些纳米颗粒的尺寸与链段相当。目标1和2将揭示多尺度动力学上聚合物-纳米颗粒相互作用和分子量的相互作用。目标3：利用新发展的荧光技术，有效地研究高分子体系的多尺度动力学。实验数据的模型，如非均相劳斯模型的比较，将提供新的见解在非均相聚合物体系中的链段整个链运动的解耦。预计这种解耦将允许通过添加超小纳米颗粒或通过设计具有最佳单体序列的聚合物来简单地改变流变特性。该奖项反映了NSF的法定使命，并被认为是值得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的支持。

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.