Polymer membranes find use in a variety of important applications such as energy storage devices, water purification, and gas separation. Despite the long history of polymer membranes, knowledge about the relationship between their multi-scale structure and macroscopic transport properties is not well developed. This limited knowledge has hindered many practical applications of polymer membranes.<br/>We are investigating lithium-form perfluorosufonic acid (Nafion) membranes by NMR diffusometry and determine the activation energy of diffusion at various hydration levels for two distinctly different moving species, lithium ions and water molecules. Combination of these NMR diffusometry experiments with molecular dynamics (MD) simulations as a function of ion-water mole ratio and nanoconfined model representatives of membranes provides insight into the relationship between diffusion behavior and local molecular environment. The MD model (see figure) simulates water and ion diffusion in the Nafion hydrophilic nanochannels. The model consists of a variable-diameter (1 – 3 nm) single wall carbon nanotube with sulfonate groups on the inner wall filled with water and Li<sup>+</sup> counterions. The synergy between NMR measurements and atomistic simulations affords deeper fundamental understanding of transport processes, and guides the design and optimization of materials for wide-ranging molecular transport and separations applications.

Understanding transport in polymeric separations membranes by combining NMR diffusometry and molecular dynamics simulations

255th National Meeting (2018)

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