Cooperative Transport in Ion-Conducting Membranes

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Ion-containing polymer membranes are critical components in many technologies including chemical separations, water purification, fuel cells, and other energy generation and storage devices. In solar-fuel devices, ion-containing polymer membranes are responsible for permitting the selective transport of ions between electrodes to maintain overall charge neutrality yet limit the transport of oxidation and reduction products produced at the electrodes. Improvements in membrane technology for these applications requires new material development that will rely on fundamental understanding of the relationships between polymer membrane structure and the transport of ions, molecules and complex mixtures. This project leverages a tunable membrane design strategy to investigate fundamental relationships between membrane structure, membrane physicochemical properties, and membrane-transport behavior of ion-containing polymer membranes. Results from this study will provide fundamental structure-property relations which will guide the future design of ion-containing polymer membranes. The research will train undergraduate and graduate students in cutting edge research in membrane science and engage students from underrepresented groups in STEM fields. The investigators will also develop and disseminate hands-on educational and outreach activities, including undergraduate independent study experiences and exploratory modules related to STEM and membrane science through summer research experiences and primary education outreach including summer engineering camps for high school students.The goal of this research is to elucidate how co-transporting neutral species impact the transport of charged species in ion containing polymer membranes with membrane-bound anions (cation exchange membranes). The research hypothesis is that the presence of neutral species reduces electrostatic interactions (i.e. Donnan exclusion) that occur between membrane-bound sulfonate anions and permeating anions, leading to increased permeability of the charged solute. PEGDA-based membranes with systematically varied membrane structure, fractional free volume, and ion content will be synthesized and the impact of membrane chemistry on physiochemical properties will be characterized. Fundamental solute-solute and solute-membrane interactions will be systematically elucidated using a tunable synthetic design strategy based on photopolymerization of acrylates and diacrylates to control polymer membrane structure, bound ion content, and water uptake. Transport properties (i.e. permeability, solubility, and diffusivity) will be investigated experimentally for a neutral solute (methanol), an ionic solute (acetate), and their complex mixture. Permeation experiments will be conducted using custom-built diffusion cells outfitted to monitor receiver cell solute concentrations using ATR FTIR spectroscopy enabling simultaneous characterization of multiple simultaneous solute concentrations. This research will have the potential to impact the design of new membrane materials for a variety of applications, such as materials for water purification, and energy devices such as solar fuels 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.