Fundamental Water and Ion Transport Properties in Polymers for Membrane Applications

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Intellectual Merit: According to the National Academy of Engineering, one of the ?Grand Challenges for Engineering? is providing access to clean water for mankind.1 The development of energy-efficient methods to provide adequate access to clean water for a variety of agricultural, industrial and municipal applications is an urgent and critical problem in many parts of the world. Polymer membranes play a central role in water purification today, and because they are often more energy-efficient than conventional technologies, their role in water purification is increasing. A key challenge in purifying water from brackish or seawater sources is removal of ions (i.e., desalination). While reverse osmosis (RO) membranes are widely used for desalination, there are a plethora of other membrane-based techniques (e.g., forward osmosis, electrodialysis, reverse electrodialysis, and membrane-assisted capacitive deionization) that could contribute significantly to water purification and power generation in the future. However, much remains unknown about even basic relationships between polymer structure and ion and water transport properties, and such information is critical for rationally tailoring new membranes for such applications. Therefore, the experimental research project will investigate fundamental water and salt transport properties in a variety of polymers to develop structure-property relationships to assist in designing and optimizing next generation polymer membranes for water/ion separations. For desalination membrane materials, one objective of the proposed program will be to understand how polymer structures can be optimized to simultaneously increase water permeability while maintaining or decreasing salt permeability. The project will consider a variety of materials to span a wide polymer structure spectrum. The influence of polymer charge, backbone rigidity, cross-linking, and morphology/polymer architecture (e.g., block copolymers) on water and ion transport properties will be studied. The investigators will also characterize the impact of mono-/divalent ion concentration on water and ion transport properties. Results from these studies will provide fundamental structure/property relations to guide the rational tailoring of polymers for desalination or other applications, such as those mentioned above. When possible, experimental results will be compared with existing models. In this regard, available models, such as free volume theory (for water and ion diffusion properties) and Donnan equilibrium (for ion partitioning), will be used in data analysis/interpretation to construct and validate a systematic, fundamental framework for organizing experimental data into structure/property correlations that can be used to guide selection of next-generation structures with more favorable property profiles for a given application. The proposed research program is well suited for developing fundamental knowledge and understanding through systematic hypothesis-driven studies. Broader Impacts: The proposed study will include STEM education programs for pre-K through undergraduate students, and students from underrepresented groups will be encouraged to participate in these opportunities. For example, The investigators will organize separations modules to be presented at Science Sundays at the Austin Children?s Museum, which reaches a broad spectrum of children, including many children of Hispanic origin. They will also partner with the Texas School for the Deaf to bring hearing-impaired high school students to their laboratories for after-school and summer research experiences. All students engaging in the proposed research program or the outreach programs will gain critical research skills while formulating, conducting, and analyzing data from hypothesis-driven experiments. Results will be published in the peer-reviewed and, when appropriate, patent literature so that the knowledge gained during the proposed program will be available to guide and educate future researchers. We would also present the work at scientific conferences. Society-at-large will benefit because improved fundamental understanding of relationships between polymer structure and water/ion transport properties will enable more rapid development of improved polymers for desalination and other membrane-based processes involving water and ion transport. In desalination, such membranes could provide populations in water-stressed regions with critically needed water while reducing the energy and environmental cost of desalination.