Computational-Experimental Insight across Time and Length Scales of Dynamics in Ionic Polymers

非技术概述：新材料的设计是设计新平台的一个关键方面，这些平台将增强国家的能源安全，影响健康，并提高经济竞争力。推动清洁能源生产和储存等技术以及众多生物医学技术的创新需要能够同时具有不同能力的新材料。一类很有前途的材料由非常大的分子(聚合物)组成，能够传输离子和电子，同时保持其机械完整性，通常在可能影响其性能的高温、溶剂和外部应力的极端条件下。这些材料发挥多种作用的能力是通过将具有不同化学功能的分子片段定制成一个大分子来实现的，包括用于传输离子和电子的块和提供机械稳定性的块。在这些细分市场集成到设备中时，控制它们的组织和执行方式是设计新的有效平台的关键。在这个项目中，使用大规模的计算研究结合最先进的中子测量，这些聚合物的结构的影响将与它们在高温和溶剂中暴露时的动力学相关联。预计的结果将提供理解，提高设计控制良好的多功能聚合物的能力，为特定应用量身定做所需的性能。该项目与研究生和本科生的跨学科教育和培训以及高中出游紧密结合在一起。技术摘要：由可电离嵌段(离聚体或聚电解质)与具有明确定义的功能的更多链段连接组成的聚合物，是从清洁能源和存储到传感器和药物输送工具等大量应用的有前景的介质。离子基团的作用是双重的：它们形成物理交联键，同时促进离子和极性客体分子的运输。由于这两种功能通常需要性质相反的动力学，额外的嵌段会影响此类聚合物的整体稳定性。在这里，使用大规模分子动力学模拟结合中子散射技术，将研究聚合物动力学与离子缔合及其内聚性之间的相关性，这些聚合物由一系列模型共聚物组成，这些共聚物以苯乙烯磺酸盐为离子嵌段，与不同的非离子链段相连。许多研究已经探索了含离子聚合物和聚电解质的结构，揭示了丰富多样的形态，并在结构和传输之间建立了明确的关联。这些研究提出的一个关键挑战是需要揭示离子缔合及其对聚合物流动性的影响之间的相关性。动力学与离子缔合的数目、拓扑和稳定性的关系影响聚合物的性质，进而影响大量技术。这项研究旨在解决离子缔合形成的约束对聚合物动力学的影响。计算技术的进步，加上中子散射的新发展，将使人们能够对物理交联链限制下的聚合物的动力学有一个新的见解。

NON-TECHNICAL SUMMARY:The design of new materials is one critical aspect of engineering new platforms that will augment the energy security of the nation, impact health, and enhance economic competitiveness. Driving innovation in technologies such as clean energy generation and storage and numerous biomedical technologies requires new materials that can serve in different capacities simultaneously. One promising class of materials consists of very large molecules (polymers) able to transport ions and electrons while retaining their mechanical integrity, often under extreme conditions of high temperatures, solvents, and external stresses that may affect their performance. The ability of these materials to play multiple roles is attained by tailoring molecular segments with different chemical functionalities into one large molecule, including blocks for transporting ions and electrons and blocks to provide mechanical stability. Controlling the way these segments organize and perform electrically as they are integrated into devices is key to the design of new effective platforms. In this project, using large-scale computational studies coupled with state-of-the-art neutron measurements, the effects of the structure of these polymers will be correlated with their dynamics as they are exposed to high temperatures and solvents. The projected results will provide the understanding that will enhance the ability to design well-controlled multi-functional polymers, tailored with desired properties for specific applications. The project is closely integrated with interdisciplinary education and training of graduate and undergraduate students and high-school outreach.TECHNICAL SUMMARY:Polymers that consist of ionizable blocks (ionomers, or polyelectrolytes) tethered to additional segments with well defined functionalities, constitute promising media for a large number of applications from clean energy and storage to sensors and drug delivery vehicles. The role of the ionic groups is two-fold: they form physical crosslinks while facilitating transport of ions and polar guest molecules. As these two functions often require dynamics of opposing nature, the additional blocks affect the overall stability of such polymers. Here, using large-scale molecular dynamics simulations coupled with neutron scattering techniques, the correlation of polymer dynamics with ionic associations and their cohesiveness will be investigated on a series of model copolymers that consist of styrene sulfonate as the ionic block tethered to different non-ionic segments. Numerous studies have probed the structure of ion-containing polymers and polyelectrolytes, revealing a rich variety of morphologies and establishing a clear correlation between structure and transport. One key challenge that arises from these studies is the need to unfold the correlation between ionic associations and their impact on the mobility of the polymers. The relationship of the dynamics with the number, topology, and stability of the ionic associations impacts the polymer properties and in turn affects a large number of technologies. This research is set to resolve the effects of constraints formed by ionic associations on polymer dynamics. Advances in computational techniques coupled with new developments in neutron scattering will enable a new insight into the dynamics of polymers under the confinement of physical crosslinks.