Partial molar volume and compressibility of alkali-halide ions in aqueous solution: Hydration shell analysis with an integral equation theory of molecular liquids
Partial molar volume and compressibility of alkali-halide ions in aqueous solution: Hydration shell analysis with an integral equation theory of molecular liquids
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DOI：
10.1021/jp014504a
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发表时间：
2002-07-25
影响因子：
3.3
通讯作者：
Hirata, F
中科院分区：
文献类型：
--
作者：
Imai, T;Nomura, H;Hirata, F
基于RISM-Kirkwood-Buff理论计算了无限稀释水溶液中碱卤离子的偏摩尔体积和偏摩尔压缩系数。理论结果与相应的实验数据定性一致。体积和压缩性值被分解成体积排斥和电致伸缩的贡献。体积排阻效应定性地决定了偏摩尔体积对离子尺寸的依赖性，而电致伸缩效应在偏摩尔压缩性的尺寸依赖性中占主导地位。偏摩尔体积和压缩性进一步分析，通过使用水化壳模型，使我们能够区分每个水化壳的贡献。对于初级水化壳层，我们可以联系到Frank-Wen和Samoilov提出的离子水化的经典模型。紧邻离子的水分子总是对离子的偏摩尔体积有负贡献。第一水化壳层对Samoilov模型中“正水化”离子的偏摩尔压缩系数有负贡献，对“负水化”离子的偏摩尔压缩系数有相反贡献。从热力学响应函数的朗道涨落公式的观点出发，用离子周围的密度涨落来解释负水合离子周围的水结构更具可压缩性的原因。
The partial molar volume and partial molar compressibility of alkali-halide ions in aqueous solution at infinite dilution are calculated based on the RISM-Kirkwood-Buff theory. The theoretical results are in qualitative agreement with the corresponding experimental data. The volume and compressibility values are decomposed into the volume-exclusion and electrostriction contributions. The volume-exclusion effect qualitatively determines the dependence of the partial molar volume on the ion size, whereas the electrostriction effect dominates in the size dependence of the partial molar compressibility. The partial molar volume and compressibility are further analyzed by using the hydration shell model which enables us to distinguish a contribution from each hydration shell. For the primary hydration shell, we can make contact with the classical models of ion hydration proposed by Frank-Wen and Samoilov. Water molecules in the immediate vicinity of an ion always give a negative contribution to its partial molar volume. The first hydration shell makes a negative contribution to the partial molar compressibility for the ions classified with the "positive hydration" in terms of Samoilov's model and does the opposite contribution for those with the "negative hydration". The reason the water structure around a negatively hydrated ion is more compressible is explained in terms of density fluctuations around the ions from a viewpoint of the Landau fluctuation formula for the thermodynamic response functions.