Collaborative: The Polyelectrolyte-Ionomer Transition in Polymers

技术概述主链上带有电荷，沿着中和小分子抗衡离子的聚合物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，相当大一部分抗衡离子从链中解离出来，可以在系统中自由移动。相反，在离聚物的情况下，几乎所有的抗衡离子都强烈地凝聚在链上，并且另外这些中性电荷对可以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，但这被隔离聚集体的存在可以使离子传导成为非常缓慢的传输过程的事实所缓解。目的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宽范围内改变温度而改变。聚集将直接通过STEM和SAXS和SANS进行研究。 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，并且流变学强烈取决于抗衡离子是游离的、成对的还是成簇的。最近开发的介电谱方法将确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。这些研究将补充计算机模拟，采用蒙特卡罗和分子动力学方法。 非技术性总结这项研究的智力价值将是对离子配对和离子对聚类的更好理解，最终发展出一种新的模型，该模型充分详细描述了从聚乙烯到离聚物的过渡。 此类含离子聚合物具有相当大的兴趣，因为它们已被提议用于致动器、燃料电池膜电极组件和用于先进电池的阳离子导电介质。 因此，这项研究将有助于聚合物的设计，驱动器，燃料电池和电池。 能源领域的材料开发预计将在美国未来的经济和生活方式中发挥非常重要的作用。 在这个"能源材料"竞技场训练的研究生将在美国工业界和学术界的巨大需求。 PSU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（在过去的10年里，我们的本科研究人员中有14/23进入了科学和工程研究生院），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'