CAREER: Charge Delocalization: A New Tool for Controlling Ionic Selectivity and Conductivity of Ion-Exchange Membranes

高度受损水域（即含有高浓度盐和其他溶解溶质的水域）的管理对于海水淡化和水力压裂等应用至关重要。盐水管理的困难阻碍了这类应用的发展，最终影响到我国的水和能源安全。电渗析是一种基于膜的技术，它利用带电的聚合物膜和电来分离离子，将它们从水中去除，已被提议用于处理高度受损的水。然而，这种技术是能源密集型和低效的，因为当接触高度受损的水时，膜的性能会显著恶化。在本研究中，将系统地研究聚合物主链上带电基团的化学性质与膜性能之间的关系。这种结构/性能关系的发展将指导膜的设计，当与高度受损的水接触时，膜的传输性能得到改善。为了加强低社会经济地位学生对STEM的参与，将为高中生制定一个全面的暑期研究计划。该计划将包括动手实验室工作，膜科学的短期课程，并通过与密歇根大学自然历史博物馆合作开发的外展项目将结果传播给广泛而多样化的受众。离子交换膜（IEMs）用于通过电渗析处理高度受损的水，其中含有少量的水。在这些材料中有离子配对的证据，这最终降低了膜的电荷密度，恶化了离子的电导率和选择性。假设增加固定电荷基团的电荷离域可以通过减弱固定电荷和移动离子之间的静电相互作用来增强离子电导率和低含水量IEMs的选择性。这一假设将通过结合实验和模型研究来系统地测试电荷离域对IEMs输运性质的影响。大多数用于水离子分离的IEMs都是利用磺酸阴离子或三甲基铵阳离子作为附着在聚合物主链上的带电基团，因此本项目将为用于水离子分离的IEMs开辟新的研究方向。由于拟议研究的基本性质，所产生的知识将对在低介电环境中使用IEMs的其他技术（例如，能量转换和存储设备）具有广泛的影响。该奖项反映了美国国家科学基金会的法定使命，并通过使用基金会的知识价值和更广泛的影响审查标准进行评估，被认为值得支持。

Management of highly impaired waters (i.e., waters that contain high concentrations of salts and other dissolved solutes) is critical for applications such as water desalination and hydraulic fracturing. The difficulty of brine management hinders the growth of such applications, which ultimately affects the water and energy security of our Nation. Electrodialysis, a membrane-based technology that uses charged polymer membranes and electricity to separate ions, removing them from water, has been proposed for treating highly impaired waters. However, this technology is energy intensive and inefficient because the membrane performance significantly deteriorates when contacted by highly impaired waters. In this study, the connection between the chemical identity of the charged groups on the polymer backbone and the membrane performance will be systematically investigated. The development of such structure/property relationships will guide the design of membranes with improved transport properties when contacted by highly impaired waters. To enhance the involvement of low socioeconomic status students in STEM, a comprehensive summer research program for high school students will be developed. The program will involve hands-on laboratory work, a short course on membrane science, and dissemination of the results to a broad and diverse audience via outreach programs developed via a collaboration with the University of Michigan Museum of Natural History.Ion-exchange membranes (IEMs) that are used for treating highly impaired waters via electrodialysis contain low amounts of water. There is evidence of ion pairing in such materials, which ultimately decreases the charge density of the membrane and worsens both the ionic conductivity and selectivity. Increasing the charge delocalization of the fixed charge groups is hypothesized to enhance both the ionic conductivity and selectivity of low water content IEMs by weakening electrostatic interactions between the fixed charges and mobile ions. This hypothesis will be systematically tested via a combined experimental and modeling study on the influence of charge delocalization on transport properties of IEMs. The majority of IEMs for aqueous ion separations utilize sulfonate anions or trimethylammonium cations as the charged groups attached to the polymer backbone, so the proposed project will open up a new direction of study on IEMs for aqueous ion separations. Due to the fundamental nature of the proposed study, the knowledge generated will have broad implications for other technologies that use IEMs in low dielectric environments (e.g., energy conversion and storage devices).This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.