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Ion Correlation X-ray Spectroscopy (John Fulton, PNNL)

Title: Ion Correlation X-ray Spectroscopy Speaker: John Fulton (PNNL) Abstract: Obtaining a molecular-level understanding of aqueous ion solvation is important to a wide range of areas including biochemistry, geochemistry, battery chemistry and separations. The overwhelming majority of x-ray studies (XAFS, XES, WAXS, XRD) have only probed the local structure of ion-ion and ion-water ordering up to approximately 0.5 nm. However, electrostatic forces order ions to much longer distances. Using a combination of small x-ray scatterings (SAXS) and x-ray absorption (XAS) we have resolved the structure of ordered nanodomains (1 to 5 nm) in aqueous solutions. We have also experimentally identified the Kirkwood Transition (KT), which demarcates a concentration above which long-range ion ordering occurs. Size domains with length scales up to 5 nm are directly related to important thermodynamic properties such as ion activity coefficients and osmotic coefficients. These domains also play an important role in the formation of nucleation clusters above the saturation concentration and in long-range ion ordering that affects mesoscale processes.