Ionomer Dynamics in Confinement: Fundamental Insights from Dielectric Spectroscopy

非技术总结：这个项目将创造关于离子在含离子聚合物材料中的动态性质和运动的知识，这将有助于理解和优化下一代电源和电化学设备。特别是，当这些材料的尺寸被限制在几个纳米时，将探索它们的性能。这项研究是关于当离子聚合物被限制在多孔膜中时，与块状材料相比，其性能发生变化的方式。例如，有证据表明，一些聚合物分子将被吸附到孔表面(强烈的客体/主体相互作用)，导致聚合物运动显著减慢，离子传导性降低。当对毛孔进行化学处理以产生弱的客体/宿主相互作用时，这些表面效应可以被抵消，从而提高离子传导性。这项工作的发现将对未来电源和电化学设备的发展产生重大影响，特别是纳米特征尺寸的电源和电化学设备。在人力资源方面，该研究项目将为两名研究生创造学习机会。本科生还将通过宾夕法尼亚州立大学科学与工程女性(WISE)研究计划、高级论文项目以及宾夕法尼亚州立大学NSF-REU软材料计划的一部分，有意义地参与其中。计划参与者将被鼓励参与外展活动，特别是那些与WISE研究所相关的活动。技术摘要：该项目针对一个重要的未探索领域：纳米尺度限制对导电离聚体中离子传输的作用。受限几何构型中离子物种的迁移率是聚合物物理中的一个重要课题，在含离子聚合物纳米结构器件的设计和加工中具有重要的实际意义。研究纳米尺度的限制如何影响离聚体中的离子传输的动机源于对其性质和性能如何随着其尺寸被限制在几纳米尺度内而发生变化的探索。为此，我们对柱状二氧化硅纳米孔中两种导电离聚体体系的分子动力学进行了全面的研究。二氧化硅薄膜对这些实验特别有利，因为可以很容易地获得直径在4到10 nm范围内的孔。主体膜和客体离聚体之间强烈的界面相互作用将导致较慢的动力学过程，而纳米尺度的空间限制可以起到促进离子传输的反作用。介电光谱学是研究纳米多孔介质中聚合物动力学的理想工具，因为它能够在很宽的频率和温度范围内探测分子波动。离聚体中离子偶极子的聚集对离子传导有重要影响，特别是通过它对聚合物链段动力学的影响，而聚合物链段动力学又通常与离子传输相耦合。限制对离子偶极聚集的影响以前还没有被探索过，但在这次研究中这样做是必要的，以提供对限制在分子动力学中的作用的完整理解。

NON-TECHNICAL SUMMARY:This project will create knowledge on the dynamic properties and the motions of ions in ion-containing polymeric materials, which will facilitate understanding and optimization of next-generation power sources and electrochemical devices. In particular, the performance of these materials will be explored when their dimensions are restricted to only a few nanometers. The research deals with the way the properties of ion-containing polymers change when confined inside porous membranes, in comparison to the bulk material. For example, there is evidence that some polymer molecules will be absorbed onto the pore surface (strong guest/host interaction) resulting in significant slowing of polymer motions and reduced ion conductivity. These surface effects can be negated when the pores are chemically treated to create weak guest/host interactions, resulting in enhanced ion conductivity. The findings of this work can have a significant impact on the future development of power sources and electrochemical devices, particularly those with nanometer feature sizes.In terms of human resources, this research project will create learning opportunities for two graduate students. Undergraduate students will also participate meaningfully, through the Penn State Women in Science and Engineering (WISE) Research program, senior thesis projects, and as part of the Penn State NSF-REU program on soft materials. Program participants will be encouraged to engage in outreach activities, particularly those connected with the WISE Institute.TECHNICAL SUMMARY:This project targets an important unexplored area: the role of nanoscale confinement on ion transport in conductive ionomers. The mobility of ionic species in confined geometries is an important topic in polymer physics and has future practical relevance in the design and processing of ion-containing polymer nanostructured devices. The motivation for investigating how nanoscale confinement influences ion transport in ionomers arises from the quest to understand how their properties and performance change as their dimensions are restricted to length scales of a few nanometers. To this end, a comprehensive investigation of the molecular dynamics of two conductive ionomer systems confined in cylindrical silica nanopores is proposed. Silica membranes are particularly advantageous for these experiments, as pores with diameters in the range of 4 to 10 nm can be readily achieved. Strong interfacial interactions between the host membrane and guest ionomer will lead to slower dynamics, while spatial restriction at the nanometer length scale can have the reverse effect of enhancing ion transport. Dielectric spectroscopy is an ideal tool to investigate the dynamics of polymers in nanoporous media owing to its ability to probe molecular fluctuations over a wide frequency and temperature range. Aggregation of ion dipoles in ionomers has important consequences for ion conduction, particularly through its influence on polymer segmental dynamics, which in turn is generally coupled with ion transport. The influence of confinement on ion dipole aggregation has not been explored previously, but it is essential to do so in this investigation to provide a complete understanding of the role of confinement on the molecular dynamics.