Assessing long-range contributions to the charge asymmetry of ion adsorption at the air–water interface,Chemical Science

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Assessing long-range contributions to the charge asymmetry of ion adsorption at the air–water interface
Chemical Science ( IF 7.6 ) Pub Date : 2020-10-05 , DOI: 10.1039/d0sc01947j
Stephen J. Cox _{1,

2,

3,

4} , Dayton G. Thorpe _{5,

6,

7,

8,

9} , Patrick R. Shaffer _{1,

7,

8,

10} , Phillip L. Geissler _{1,

5,

6,

7,

8}

Affiliation

Anions generally associate more favorably with the air–water interface than cations. In addition to solute size and polarizability, the intrinsic structure of the unperturbed interface has been discussed as an important contributor to this bias. Here we assess quantitatively the role that intrinsic charge asymmetry of water's surface plays in ion adsorption, using computer simulations to compare model solutes of various size and charge. In doing so, we also evaluate the degree to which linear response theory for solvent polarization is a reasonable approach for comparing the thermodynamics of bulk and interfacial ion solvation. Consistent with previous works on bulk ion solvation, we find that the average electrostatic potential at the center of a neutral, sub-nanometer solute at the air–water interface depends sensitively on its radius, and that this potential changes quite nonlinearly as the solute's charge is introduced. The nonlinear response closely resembles that of the bulk. As a result, the net nonlinearity of ion adsorption is weaker than in bulk, but still substantial, comparable to the apparent magnitude of macroscopically nonlocal contributions from the undisturbed interface. For the simple-point-charge model of water we study, these results argue distinctly against rationalizing ion adsorption in terms of surface potentials inherent to molecular structure of the liquid's boundary.

中文翻译：

评估对空气-水界面处离子吸附的电荷不对称性的长期贡献

与阳离子相比，阴离子通常更有利于与空气-水界面结合。除了溶质的大小和极化性之外，还讨论了不受干扰的界面的固有结构，这是造成这种偏差的重要原因。在这里，我们使用计算机仿真来比较各种大小和电荷的模型溶质，从而定量评估水表面固有电荷不对称性在离子吸附中的作用。在此过程中，我们还评估了溶剂极化线性响应理论是比较本体和界面离子溶剂化热力学的合理方法的程度。与先前关于体离子溶剂化的工作一致，我们发现在空气-水界面处的中性，亚纳米级溶质中心的平均静电势敏感地取决于其半径，当引入溶质的电荷时，该电势会非线性地变化。非线性响应与本体响应非常相似。结果，离子吸附的净非线性比整体的弱，但仍然相当可观，与不受干扰的界面在宏观上的非局部贡献的表观幅度相当。对于我们研究的水的单点电荷模型，这些结果明显反对使离子吸附合理化，这是液体边界分子结构固有的表面电势所致。可与不受干扰的界面对宏观非局部贡献的表观大小进行比较。对于我们研究的水的单点电荷模型，这些结果明显反对使离子吸附合理化，这是液体边界分子结构固有的表面电势所致。可与不受干扰的界面对宏观非局部贡献的表观大小进行比较。对于我们研究的水的单点电荷模型，这些结果明显反对使离子吸附合理化，这是液体边界分子结构固有的表面电势所致。

更新日期：2020-10-12

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