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首页> 外文期刊>Proceedings of the National Academy of Sciences of the United States of America >On the fluctuations that drive small ions toward, and away from, interfaces between polar liquids and their vapors
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On the fluctuations that drive small ions toward, and away from, interfaces between polar liquids and their vapors

机译：驱使小离子朝向和远离极性液体与其蒸气之间的界面的波动

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Contrary to the expectations from classic theories of ion solvation, spectroscopy and computer simulations of the liquid-vapor interface of aqueous electrolyte solutions suggest that ions little larger than a water molecule can prefer to reside near the liquid's surface. Here we advance the view that such affinity originates in a competition between strong opposing forces, primarily due to volume exclusion and dielectric polarization, that are common to all dense polar liquids. We present evidence for this generic mechanism from computer simulations of (ⅰ) water and (ⅱ) a Stockmayer fluid near its triple point. In both cases, we show that strong surface enhancement of small ions, obtained by tuning solutes' size and charge, can be accentuated or suppressed by modest changes in either of those parameters. Statistics of solvent polarization, when the ion is held at and above the Gibbs dividing surface, highlight a basic deficiency in conventional models of dielectric response, namely, the neglect of interfacial flexibility. By distorting the solution's boundary, an ion experiences fluctuations in electrostatic potential and in electric field whose magnitudes attenuate much more gradually (as the ion is removed from the liquid phase) than for a quiescent planar interface. As one consequence, the collective responses that determine free energies of solvation can resolve very differently in nonuniform environments than in bulk. We show that this persistence of electric-field fluctuations additionally shapes the sensitivity of solute distributions to ion polarizability.
机译：与经典的离子溶剂化理论所期望的相反，电解质水溶液的液-气界面的光谱学和计算机模拟表明，比水分子大一点的离子可能更喜欢留在液体表面附近。在这里，我们提出这样一种观点，即这种亲和力主要来自所有稠密极性液体共有的强相反力之间的竞争，主要是由于体积排斥和介电极化。我们通过（ⅰ）水和（ⅱ）三点附近的Stockmayer流体的计算机模拟提供了这种通用机制的证据。在这两种情况下，我们都表明，通过调整溶质的大小和电荷而获得的小离子的强表面增强作用，可以通过这些参数中的任何一个的适度变化而加重或抑制。当离子保持在吉布斯分割面及其上方时，溶剂极化的统计数据突显了常规电介质响应模型中的一个基本缺陷，即忽略了界面柔性。通过使溶液的边界变形，离子会经历静电势和电场的波动，其幅度的衰减要比静态平面界面的衰减要大得多（随着离子从液相中的去除）。结果，决定溶剂化自由能的集体反应在非均匀环境中的分辨能力与在整体环境中的分辨力非常不同。我们表明，电场波动的这种持久性还会影响溶质分布对离子极化性的敏感性。

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