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

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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.