Kim Jeongmin, Rotenberg Benjamin
Department of Energy Engineering, Korea Institute of Energy Technology (KENTECH), Naju 58330, Republic of Korea.
Sorbonne Université, CNRS, Physico-chimie des Électrolytes et Nanosystèmes Interfaciaux, PHENIX, F-75005 Paris, France.
J Chem Phys. 2024 Aug 7;161(5). doi: 10.1063/5.0220913.
Ion partitioning between different compartments (e.g., a porous material and a bulk solution reservoir), known as Donnan equilibrium, plays a fundamental role in various contexts such as energy, environment, or water treatment. The linearized Poisson-Boltzmann (PB) equation, capturing the thermal motion of the ions with mean-field electrostatic interactions, is practically useful to understand and predict ion partitioning, despite its limited applicability to conditions of low salt concentrations and surface charge densities. Here, we investigate the Donnan equilibrium of coarse-grained dilute electrolytes confined in charged slit-pores in equilibrium with a reservoir of ions and solvent. We introduce and use an extension to confined systems of a recently developed hybrid nonequilibrium molecular dynamics/grand canonical Monte Carlo simulation method ("H4D"), which enhances the efficiency of solvent and ion-pair exchange via a fourth spatial dimension. We show that the validity range of linearized PB theory to predict the Donnan equilibrium of dilute electrolytes can be extended to highly charged pores by simply considering renormalized surface charge densities. We compare with simulations of implicit solvent models of electrolytes and show that in the low salt concentrations and thin electric double layer limit considered here, an explicit solvent has a limited effect on the Donnan equilibrium and that the main limitations of the analytical predictions are not due to the breakdown of the mean-field description but rather to the charge renormalization approximation, because it only focuses on the behavior far from the surfaces.
离子在不同隔室（例如多孔材料和本体溶液储库）之间的分配，即唐南平衡，在能源、环境或水处理等各种领域中起着基础性作用。线性化的泊松 - 玻尔兹曼（PB）方程，通过平均场静电相互作用捕捉离子的热运动，尽管其在低盐浓度和表面电荷密度条件下适用性有限，但对于理解和预测离子分配实际上很有用。在这里，我们研究了限制在带电狭缝孔中的粗粒稀电解质与离子和溶剂储库处于平衡时的唐南平衡。我们引入并使用了一种对最近开发的混合非平衡分子动力学/巨正则蒙特卡罗模拟方法（“H4D”）的受限系统扩展，该方法通过第四空间维度提高了溶剂和离子对交换的效率。我们表明，通过简单地考虑重整化表面电荷密度，线性化PB理论预测稀电解质唐南平衡的有效范围可以扩展到高电荷孔。我们与电解质隐式溶剂模型的模拟进行了比较，并表明在此处考虑的低盐浓度和薄电双层极限下，显式溶剂对唐南平衡的影响有限，并且分析预测的主要局限性不是由于平均场描述的失效，而是由于电荷重整化近似，因为它只关注远离表面的行为。
