Collaborative: The Polyelectrolyte-Ionomer Transition in Polymers

技术概述主链上带有电荷的聚合物，连同中和小分子反离子，被称为聚电解质或离聚体。这些不同项之间的主要区别因素是电荷的聚集状态：在聚电解质的情况下，相当大一部分反离子从链上解离，并可以在系统中自由移动。相反，在离聚体的情况下，几乎所有的反离子都强烈凝聚到链上，此外，这些中性电荷对可能形成许多离子对的中性聚集体。虽然这些材料的吸引力来自于它们选择性地单独传输阳离子，但由于孤立聚集体的存在会使离子传导成为一个非常缓慢的传输过程，这一点得到了缓解。我们的目标是了解控制离子配对形成孤立偶极子的因素，以及驱动这些偶极子自组装成聚集体的进一步因素。相对非极性聚合物的介电常数可以通过加入高介电常数的溶剂和在很大范围内改变温度来改变。聚合将直接通过STEM以及SAXS和SAN进行研究。也将使用不太直接的技术，如机械流变学和DSC，其中离子对到聚集体的自组装与类似于玻璃化转变的特征相关联，而流变学强烈依赖于反离子是自由的、配对的还是簇生的。最近开发的介电光谱方法将确定离聚体中的自由离子含量和迁移率，直接评估离子对形成的程度。这些研究将得到计算机模拟的补充，使用蒙特卡罗和分子动力学方法。非技术概述这项研究的智力价值将是对离子对和离子对聚集的更好的理解，最终导致开发出一种新的模型，该模型完全详细地描述了从聚电解质到离聚体的转变。由于此类含离子聚合物已被用于致动器、燃料电池膜电极组件和先进电池的阳离子导电介质，因此引起了人们的极大兴趣。因此，这项研究应该有助于执行器、燃料电池和电池的聚合物设计。预计能源领域的材料开发将在美国未来的经济和生活方式中发挥非常重要的作用。在这一‘能源材料’领域接受培训的研究生将在美国工业界和学术界产生巨大的需求。巴黎州立大学和哥伦比亚大学都有优秀的本科生，研究促使他们进入研究生院(在过去的10年里，我们有14/23的本科生进入了科学和工程研究生院)，许多现在的本科生对‘能源材料’感兴趣。

Technical SummaryPolymers with charges on their backbones, along with neutralizing small molecule counterions, are termed polyelectrolytes or ionomers. The chief distinguishing factors between these different terms is the state of aggregation of the charges: in the case of polyelectrolytes, a significant fraction of the counterions are dissociated from the chain and can move freely through the system. In contrast, in the case of ionomers, nearly all counterions are strongly condensed onto the chain, and additionally these neutral charge pairs may form neutral aggregates of many ion pairs. While the attractiveness of these materials comes from the fact that they selectively transport cations alone, this is mitigated by the fact that the presence of isolated aggregates can make ion conduction a very slow transport process. The goal is to understand the factors which control the ion pairing to form isolated dipoles, and the further factors which drive these dipoles to self-assemble into aggregates. The dielectric constant of a relatively nonpolar polymer will be changed by adding a high dielectric constant solvent and vary temperature over a wide range. Aggregation will be studied directly through STEM and both SAXS and SANS. Less direct techniques will also be used, such as mechanical rheology and DSC, where self-assembly of ion pairs into aggregates is associated with a signature that is akin to a glass transition and rheology strongly depends on whether the counterions are free, paired or clustered. Recently developed dielectric spectroscopy methods will determine free ion content and mobility in ionomers, directly assessing the extent of ion pair formation. These studies will be complimented by computer simulations, employing Monte Carlo and Molecular Dynamics methods. Non-Technical SummaryThe intellectual merit of this research will be an improved understanding of ion-pairing and ion-pair clustering, culminating in the development of a new model that fully details the transition from polyelectrolyte to ionomer. Such ion-containing polymers are of considerable interest since they have been proposed for use in actuators, fuel cell membrane electrode assemblies and for the cation conduction medium for advanced batteries. Hence, this research should facilitate polymer design for actuators, fuel cells and batteries. Materials development in the energy field is expected to play a very important role in the future of the United States economy and way of life. Graduate students trained in this 'energy materials' arena will be in enormous demand in both US industry and academia. PSU and Columbia have superb undergraduates and research motivates them to attend graduate school (14/23 of our undergraduate researchers have gone on to graduate school in science and engineering over the past 10 years) with many current undergraduates interested in 'energy materials'