Collaborative: The Polyelectrolyte-Ionomer Transition in Polymers

技术摘要主链上带有电荷以及中和小分子抗衡离子的聚合物被称为聚电解质或离聚物。这些不同术语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，很大一部分抗衡离子从链上解离，并且可以在系统中自由移动。相反，在离聚物的情况下，几乎所有抗衡离子都强烈凝聚在链上，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的事实，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，这一事实削弱了这一点。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将通过添加高介电常数溶剂和在较宽范围内改变温度来改变。将通过 STEM 以及 SAXS 和 SANS 直接研究聚合。 还将使用不太直接的技术，例如机械流变学和 DSC，其中离子对自组装成聚集体与类似于玻璃化转变的特征相关，而流变学在很大程度上取决于反离子是游离的、成对的还是成簇的。最近开发的介电光谱方法将测定离聚物中的自由离子含量和迁移率，直接评估离子对形成的程度。这些研究将得到采用蒙特卡罗和分子动力学方法的计算机模拟的补充。 非技术摘要这项研究的智力价值将是提高对离子对和离子对聚类的理解，最终开发出一个新模型，全面详细介绍从聚电解质到离聚物的转变。 这种含离子聚合物引起了相当大的兴趣，因为它们已被提议用于致动器、燃料电池膜电极组件以及先进电池的阳离子传导介质。 因此，这项研究应该有助于执行器、燃料电池和电池组的聚合物设计。 能源领域的材料发展预计将对美国未来的经济和生活方式发挥非常重要的作用。 美国工业界和学术界对“能源材料”领域培训的研究生都有巨大的需求。 匹兹堡州立大学和哥伦比亚大学拥有优秀的本科生，研究激励他们进入研究生院（过去 10 年，我们的本科生研究人员中有 14/23 进入了科学与工程研究生院），许多当前的本科生对“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'