Aqueous electrolyte solutions are central to many natural phenomena and industrial applications. This leads to the continuous development of increasingly complex analytical models to predict their chemical properties. These are all based on an explicit, atomistic description of ion-ion electrostatic interactions combined with mean-field approaches for the dielectric response of water. Such approaches approximate the complex multi-body ion-ion correlations to pair interactions, introducing the concept of ion-pairs. Despite many achievements, these concepts fail to describe situations where ion-ion correlation and specific solvation become relevant, such as for concentrated electrolyte solutions. Here, we propose a change of perspective, by introducing a statistical, coarse-grained view that bypasses the need to define ion pairs, and does not require any prior knowledge of specific solvation. We base our concept on separating the solution into a spherical observation droplet whose size and average composition are fully determined by the solution parameters and the environment of the remaining solution. This allows us to express the droplet-environment interaction in terms of a generalized multipole expansion, i.e. in a convenient, additive way. We applied this approach to 139 electrolytes including some ionic liquids and notoriously complex electrolytes, such as LiCl or ZnCl2. Our model yields a set of analytical functions sharing the same parameters that simultaneously model the activity coefficient, the osmotic coefficient, and water activity, Those parameters give direct access to the radius-dependent partition function around the observation droplet. The functions predict electrolyte behavior over the whole electrolyte mole fraction range, paving the road toward understanding super-saturated and water-in-salt solutions and electrolyte nucleation.

中文翻译：

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电解质水溶液的新视角


水性电解质溶液是许多自然现象和工业应用的核心。这导致了越来越复杂的分析模型不断开发，以预测其化学性质。这些都是基于对离子-离子静电相互作用的明确原子描述，并结合了水介电响应的平均场方法。这种方法将复杂的多体离子-离子相关性近似为成对相互作用，引入了离子对的概念。尽管取得了许多成就，但这些概念未能描述离子-离子相关性和特异性溶剂化变得相关的情况，例如浓电解质溶液。在这里，我们提出了一种观点的改变，通过引入一种统计的粗粒度视图，该视图绕过了定义离子对的需要，并且不需要任何特定溶剂化的先验知识。我们的概念是将溶液分离成球形观察液滴，其大小和平均成分完全由溶液参数和剩余溶液的环境决定。这使我们能够用广义多极子展开来表示液滴与环境的相互作用，即以一种方便的加法方式。我们将这种方法应用于 139 种电解质，包括一些离子液体和众所周知的复杂电解质，例如 LiCl 或 ZnCl2。我们的模型产生了一组解析函数，这些函数共享相同的参数，同时对活性系数、渗透系数和水活性进行建模，这些参数可以直接访问观测液滴周围的半径依赖性分区函数。 这些函数可预测整个电解质摩尔分数范围内的电解质行为，为理解过饱和和盐包水溶液以及电解质成核铺平了道路。