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首页> 外文期刊>Proceedings of the National Academy of Sciences of the United States of America >Elucidating the mechanism of selective ion adsorption to the liquid water surface
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Elucidating the mechanism of selective ion adsorption to the liquid water surface

机译：阐明选择性离子吸附到液态水表面的机理

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摘要

Adsorption of aqueous thiocyanate ions from bulk solution to the liquid/vapor interface was measured as a function of temperature by resonant UV second harmonic generation spectroscopy. The resulting adsorption enthalpy and entropy changes of this prototypical chaotrope were both determined to be negative. This surprising result is supported by molecular simulations, which clarify the microscopic origins of observed thermodynamic changes. Calculations reveal energetic influences of adsorbed ions on their surroundings to be remarkably local. Negative adsorption enthalpies thus reflect a simple repartitioning of solvent density among surface, bulk, and coordination regions. A different and much less spatially local, mechanism underlies the concomitant loss of entropy. Simulations indicate that ions at the interface can significantly bias surface height fluctuations even several molecular diameters away, imposing restrictions consistent with the scale of measured and computed adsorption entropies. Based on these results, we expect an ion's position in the Hofmeister lyotropic series to be determined by a combination of driving forces associated with the pinning of capillary waves and with a competition between ion hydration energy and the neat liquid's surface tension.
机译：通过共振UV二次谐波产生光谱法测量了从本体溶液到液体/蒸气界面的硫氰酸根离子水溶液的吸附随温度的变化。该原型离液剂的吸附焓和熵变均被确定为负。分子模拟支持了这一令人惊讶的结果，分子模拟阐明了观察到的热力学变化的微观起源。计算表明，吸附离子对其周围环境的能量影响非常明显。因此，负吸附焓反映了表面，主体和配位区域之间溶剂密度的简单重新分配。随之而来的熵损失是一种不同且空间上较少的局部机制。仿真表明，即使在几个分子直径之外，界面处的离子也可以显着偏向表面高度波动，从而施加与测量和计算的吸附熵的尺度一致的限制。根据这些结果，我们预计离子在霍夫迈斯特溶致系列中的位置将由与毛细波钉扎相关的驱动力以及离子水化能量与纯净液体表面张力之间的竞争所决定。

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