Quantitative Analysis of Water Activity Related to Hydration Structure in Highly Concentrated Aqueous Electrolyte Solutions

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The measurements on the activity and solvation of H₂O in hydrate melts and aqueous electrolyte solutions containing various metal chlorides were carried out by a vapor pressure measurement using a transpiration method and ¹H quantitative NMR (¹H qNMR). The electrolyte concentration dependence of the detection rate of H₂O by ¹H qNMR reflected the change of the hydration structure of the first hydration shell, and the activity of H₂O by the vapor pressure measurement clearly showed the change of the network structure of water including the first and second hydration spheres. The correlation between the enthalpy and entropy of vaporization showed the existence of different kinds of water-cation interactions.