CAREER: Nanoscale Resolution of Interfacial Materials Physics in Dry, Ionic Polymers

非技术概要：聚合物是重要的工业材料，具有柔韧性、重量轻、易于加工等特点。当正电荷或负电荷附着在这些聚合物分子上时，它们就变成了“离子聚合物”，可以应用于从柔性电池到软机器人再到可穿戴传感器的各种技术。在所有这些领域，正负极将与材料接触，聚合物/电极界面的行为将影响整体性能。在电池中，聚合物必须在电极充电/放电时粘附在电极上，以防止设备故障。对于软体机器人来说，离子和聚合物在界面处的运动决定了聚合物如何响应电信号而弯曲。该项目旨在了解聚合物的结构和动力学是如何在10-100纳米的带电表面内受到影响的，以及它与体行为有何不同。带有荧光标记的定制离子聚合物将用于选择性地探测靠近或远离电极的聚合物动力学。x射线实验将提供关于电极如何影响聚合物结构的进一步信息。这项工作的见解将用于设计下一代改进的离子材料。这种聚合物可以通过提供廉价可靠的能量存储、先进的实时可穿戴健康传感器和可用于国防目的的软自主机器人系统来造福社会。该项目将有助于学生在前沿科技领域的教育。拓展活动包括一个日间营地和周末工程博览会，从很小的年龄开始（小学到中学）。一个经常性的校外活动将举办向公众开放的讲座，以突出前沿材料研究。技术概述：本研究旨在促进对干燥、离子聚合物在体和带电界面的基本物理理解。这项工作在两个关键方面是新颖的，这将使新的基本见解成为可能。第一种是使用体积大、离域的离子基团，这削弱了电荷的相互作用，使聚合物即使在高离子含量和没有增塑剂或水（这与许多电池化学物质不相容）的情况下也能加工。二是利用荧光和时间相关x射线实验对亚10nm精度的材料物理进行空间探索。离子相互作用（包括链内和链间）对离子聚合物迁移率以及聚合物薄膜表面和界面张力的影响将被研究。由于电极或自由表面对离子聚合物的扰动将直接使用纳米尺度方法进行研究。首先，多层膜将被构建，在电极或本体上放置约10nm厚的层，以选择性地探测堆栈的区域。在单层薄膜中，相干x射线方法将探测表面波动，并提供表面动力学和表面张力如何依赖于材料中的离子相关性和结构（在单独的散射实验中确定）的信息。新的见解将提供更好地理解聚合物电解质在电极，薄膜涂层和粘合剂，以及自修复材料的物理。这项工作的一个主要贡献是发展了对离子结合和电场如何影响干燥带电聚合物扩散的分子理解。先前对聚电解质扩散的研究仅限于离子含量低（15 mol%）的体系或用水/溶剂塑化的体系，因此本研究处于离子聚合物物理的根本不同的状态。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。

NON-TECHNICAL SUMMARY:Polymers are important industrial materials that are flexible, lightweight, and readily processable. When positive or negative electric charges are attached to these polymer molecules they become "ionic polymers" which can enable applications in technologies ranging from flexible batteries to soft robotics to wearable sensors. In all of these areas, a positive and negative electrode will be in contact with the material and the behavior of the polymer/electrode interface will impact the overall performance. In batteries, polymers must adhere to the electrode as it charges/discharges to prevent device failure. For soft robots, the movement of ions and polymer at the interface determines how a polymer bends in response to an electrical signal. This project is pursuing a fundamental understanding of how the structure and dynamics of a polymer are impacted within 10-100 nanometers of a charged surface and how it is different from bulk behavior. Custom made ionic polymers with fluorescent labels will be used to selectively probe the polymer dynamics either adjacent to or far away from the electrode. X-ray experiments will provide further information on how the polymer structure is impacted by electrodes. Insights from this work will be used to design the next generation of improved ionic materials. Such polymers could benefit society by providing cheap and reliable energy storage, advanced real-time wearable health sensors, and soft autonomous robotic systems which could be deployed for defense purposes. The project will contribute to education of students in forefront scientific and technological areas. Outreach activities include a day camp and weekend engineering fair with underrepresented demographics starting at a young age (elementary to middle school). A recurring, off-campus event will host talks open to the public to highlight cutting edge materials research. TECHNICAL SUMMARY:This research seeks to advance the fundamental physical understanding of dry, ionic polymers in the bulk and at electrified interfaces. This work is novel in two key aspects which will enable new fundamental insights. The first is the use of bulky, delocalized ionic groups which weaken the charge interactions and render the polymer processable even at high ion contents and without plasticizers or water (which is incompatible with many battery chemistries). The second is the use of fluorescence and time-correlated X-ray experiments to spatially explore the material physics with sub 10-nm precision. The role of ionic interactions, both intra- and interchain, on influencing ionic polymer mobility and the surface and interfacial tension of polymer films will be investigated. Perturbations to ionic polymers due to electrodes or free surfaces will be directly investigated using nanoscale approaches. First, multilayer films will be constructed where a ca. 10 nm thick layer is placed either at the electrode or in the bulk to selectively probe regions of the stack. In single layer films, coherent X-ray methods will probe the surface fluctuations and provide information on how both surface dynamics and the surface tension depend on ionic correlations and structure (determined in separate scattering experiments) in the material. New insights will provide a better understanding of the physics of polymer electrolytes at electrodes, thin film coatings and adhesives, and self-healing materials. A major contribution of this work is developing a molecular understanding of how ionic associations and electric fields impact the diffusion of dry, charged polymers. Prior work on polyelectrolyte diffusion has been limited to systems with low ( 15 mol%) ionic content or systems that are plasticized with water/solvent, and thus this research is at a fundamentally different regime of ionic polymer physics.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.