Electrostatic potential of mean force between two curved surfaces in the presence of counterion connectivity.
Electrostatic potential of mean force between two curved surfaces in the presence of counterion connectivity.
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DOI：
10.1103/physreve.92.052317
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发表时间：
2015-11
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影响因子：
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通讯作者：
Shiqi Zhou
中科院分区：
文献类型：
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作者：
Shiqi Zhou
本文通过求解经典的密度泛函理论，研究了在原始模型电解质溶液中，反离子连接性(即反离子与链分子的缔合)对两个带电圆柱杆之间的平均静电势(EPMF)的影响。主要发现如下：(I)即使在单价反离子溶液中，反离子连接性有助于诱导类电荷吸引(LCA-like)现象，其中如果没有反离子连接性，类LCA观察通常不会发生。(Ii)对于二价反离子溶液，反离子连接性可以增强或减弱LCA式的观察，取决于链长N，并简单地将与最小EPMF对应的棒的平衡最近表面间距增加到反离子中心直径的近3倍，无论N是大是小。(3)如果N足够大，则在所考虑的整个棒表面电荷量|σ*|范围内，类LCA强度趋于与电解质浓度c负相关；而如果N减小，则随着|σ*|值的减小，相关趋于正，特别是对于中等的|σ*|值，相关关系呈现极值现象。(4)在1：1电解液的情况下，在有和没有反离子连接性的两种情况下，反离子和共离子中心直径的EPMF效应是相似的。所有这些发现都可以用最近提出的氢键风格机制来自我解释，这个机制被一个额外的概念强化了：反离子链的灵活性和影响它的因素，如N和反离子位价态。
In this paper, we investigate effects of counterion connectivity (i.e., association of the counterions into a chain molecule) on the electrostatic potential of mean force (EPMF) between two similarly charged cylinder rods in a primitive model electrolyte solution by solving a classical density functional theory. The main findings include the following: (i) The counterion connectivity helps in inducing a like-charge-attractionlike (LCA-like) phenomenology even in a monovalent counterion solution wherein the LCA-like observation generally does not occur without the counterion connectivity. (ii) For divalent counterion solutions, the counterion connectivity can reinforce or weaken the LCA-like observation depending on the chain length N, and simply increases the equilibrium nearest surface separation of the rods corresponding to the minimum EPMF to nearly three times the counterion site diameter, whether N is large or small. (iii) If N is large enough, the LCA-like strength tends to be negatively correlated with the electrolyte concentration c over the entire range of the rod surface charge magnitude |σ*| considered; whereas if N drops, the correlation tends to become positive with decrease of the |σ*| value, and particularly for modest |σ*| values, the correlation relationship exhibits an extreme value phenomenon. (iv) In the case of a 1:1 electrolyte, the EPMF effects of the diameters of counterion and coion sites are similar in both situations with and without the counterion connectivity. All of these findings can be explained self-consistently by a recently proposed hydrogen-bonding style mechanism reinforced by one additional concept: flexibility of the counterion chain and the factors affecting it, like N and counterion site valence.