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

新材料的设计是设计新平台的一个关键方面，这将增强国家的能源安全，影响健康，提高经济竞争力。 推动清洁能源生产和储存以及众多生物医学技术等技术的创新，需要能够同时发挥不同功能的新材料。一类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，通常在高温，溶剂和可能影响其性能的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剪裁成一个大分子来实现的，包括用于传输离子和电子的嵌段以及用于提供机械稳定性的嵌段。 控制这些部分在集成到设备中时的组织和电气性能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加上最先进的中子测量，这些聚合物的结构的影响将与它们暴露在高温和溶剂中的动力学相关。 预计的结果将提供理解，将提高设计良好控制的多功能聚合物的能力，为特定应用定制所需的性能。 该项目与研究生和本科生的跨学科教育和培训以及高中外展活动紧密结合。技术概要：聚合物由可电离的嵌段（离聚物或聚电解质）和具有明确功能的附加段组成，构成了从清洁能源和存储到传感器和药物输送车辆的大量应用的有前途的介质。离子基团的作用是双重的：它们形成物理交联，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相反性质的动力学，因此额外的嵌段影响此类聚合物的整体稳定性。 在这里，使用大规模的分子动力学模拟加上中子散射技术，聚合物动力学与离子协会和它们的凝聚力的相关性将研究一系列的模型共聚物，由苯乙烯磺酸盐作为离子块栓系到不同的非离子段。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相关性。从这些研究中产生的一个关键挑战是需要揭示离子缔合之间的相关性及其对聚合物流动性的影响。 动力学与离子缔合的数量、拓扑结构和稳定性的关系影响聚合物的性质，进而影响大量的技术。本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，将使人们对物理交联约束下的聚合物动力学有一个新的认识。

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.