渗透胁迫下的离子配对增强：区分离子与水活度的影响
Ion-Pairing Enhancement under Osmotic Stress: Disentangling the Effects of Ion and Water Activities
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中文总结 AI 辅助
该研究通过分子动力学模拟，分析浓KCl、NaCl和LiCl水溶液中离子配对随渗透压的变化，区分离子与水活度的影响，解释不同类型配对的相反趋势，指出离子材料中介电效应对配对的影响强于水释放。
中文摘要 AI 辅助
离子配对对渗透胁迫的依赖性可能会严重影响内部常处于渗透胁迫状态的离子材料和膜的性能，但目前对这种依赖性，特别是水和离子活度的影响的定量理解十分有限。针对这一研究空白，我们利用分子动力学模拟分析了浓KCl、NaCl和LiCl水溶液中离子配对随渗透压的增强情况。基于严格的热力学关系，我们将离子非理想性对配对常数的贡献（随渗透压变化）与其他效应（包括水释放和离子配对类型）分离开来。分析表明，离子非理想性对配对的间接影响比水释放的直接影响更强；但对于水合程度更高的配对，其影响会被大小相近且方向相反的效应所缓和，甚至可能反转，该效应源于离子配对非理想性，与溶液介电特性变化及配对时的水重构相关。这些贡献之间的相互作用，包括配对成本上显著且配对类型特异性的水合效应，解释了观测到的相反趋势：水合程度更高的溶剂分隔配对类型的配对随渗透压降低，而接触配对的配对随渗透压升高；对于水合程度更高的小阳离子，该趋势更明显，且与所用水模型基本无关。结果进一步表明，离子材料中增强的介电效应，以及由此产生的离子配对非理想性的变化比水溶液中更大，其对配对的影响应比水释放更显著。
英文摘要
The dependence of ion pairing on osmotic stress may strongly affect the performance of ionic materials and membranes whose interior is often osmotically stresses, yet quantitative understanding of this dependence and, specifically, the effects of water and ion activities is limited. Motivated by this gap, we analyze the enhancement of ion pairing with osmotic pressure for concentrated aqueous KCl, NaCl, and LiCl solutions using molecular dynamics simulations. Based on rigorous thermodynamic relations, we separate the contributions of ion non-ideality to the pairing constant, varying with osmotic pressure, from other effects including water release and type of ion-pair. Our analysis reveals that ion non-ideality indirectly generates a stronger effect on pairing than the direct one of water release. However, its effect is moderated and may even be reversed for more hydrated pairs by a similarly large and opposite effect of ion-pair non-ideality assigned to varying dielectric properties of the solution and water restructuring upon pairing. The interplay between these contributions, including large and pair type-specific hydration effects on the cost of pairing, explains the observed opposing trends: pairing decreases with osmotic pressure for more hydrated solvent-separated pair types while increasing for contact pairs. The trend becomes more pronounced for more hydrated smaller cations, but was fairly independent of the water model used. The results further suggest that dielectric effects enhanced in ionic materials-and, as a result, larger variations of ion-pair non-ideality, compared with aqueous solutions, should have a more significant impact on pairing than water release.
