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Orientational ordering of water in extended hydration shells of cations is ion-specific and correlates directly with viscosity and hydration free energy

Abstract

Specific ion effects in aqueous solutions are investigated on the molecular, nanoscopic and macroscopic level. Femtosecond elastic second harmonic scattering (fs-ESHS) is used here to assess chemical effects on molecular and nanoscopic length scales, probing changes in the charge distribution around ions as well as structural orientational order of water molecules in the extended hydration shells. We measured > 0.05 M electrolyte solutions with a series of chloride salts (LiCl, NaCl, KCl, CsCl, RbCl, NH4Cl, MgCl2, CaCl2, and SrCl2). Ion specificity is observed in both the local electronic anisotropy and the nanoscopic orientational ordering of water. Both observables are influenced more by cations with larger valencies and smaller sizes and follow a direct Hofmeister trend. These ion-induced structural changes in the hydrogen-bond network of water are strongly correlated with the viscosity B-coefficient and the Gibbs free energy of hydration of ions. Such a connection between the nanoscopic and macroscopic changes provides a possibility to construct a molecular model for specific ion effects in aqueous solutions.

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Publication details

The article was received on 20 May 2017, accepted on 07 Aug 2017 and first published on 07 Aug 2017


Article type: Paper
DOI: 10.1039/C7CP03395H
Citation: Phys. Chem. Chem. Phys., 2017, Accepted Manuscript
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    Orientational ordering of water in extended hydration shells of cations is ion-specific and correlates directly with viscosity and hydration free energy

    Y. Chen, H. I. I. Okur, C. Liang and S. Roke, Phys. Chem. Chem. Phys., 2017, Accepted Manuscript , DOI: 10.1039/C7CP03395H

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