Mucha Martin, Frigato Tomaso, Levering Lori M, Allen Heather C, Tobias Douglas J, Dang Liem X, Jungwirth Pavel
Institute of Organic Chemistry and Biochemistry, Academy of Sciences of the Czech Republic, and Center for Biomolecules and Complex Molecular Systems, Flemingovo nam. 2, 16610 Prague 6, Czech Republic.
J Phys Chem B. 2005 Apr 28;109(16):7617-23. doi: 10.1021/jp0445730.
The molecular structure of the interfacial regions of aqueous electrolytes is poorly understood, despite its crucial importance in many biological, technological, and atmospheric processes. A long-term controversy pertains between the standard picture of an ion-free surface layer and the strongly ion specific behavior indicating in many cases significant propensities of simple inorganic ions for the interface. Here, we present a unified and consistent view of the structure of the air/solution interface of aqueous electrolytes containing monovalent inorganic ions. Molecular dynamics calculations show that in salt solutions and bases the positively charged ions, such as alkali cations, are repelled from the interface, whereas the anions, such as halides or hydroxide, exhibit a varying surface propensity, correlated primarily with the ion polarizability and size. The behavior of acids is different due to a significant propensity of hydronium cations for the air/solution interface. Therefore, both cations and anions exhibit enhanced concentrations at the surface and, consequently, these acids (unlike bases and salts) reduce the surface tension of water. The results of the simulations are supported by surface selective nonlinear vibrational spectroscopy, which reveals among other things that the hydronium cations are present at the air/solution interface. The ion specific propensities for the air/solution interface have important implications for a whole range of heterogeneous physical and chemical processes, including atmospheric chemistry of aerosols, corrosion processes, and bubble coalescence.
尽管水性电解质界面区域的分子结构在许多生物、技术和大气过程中至关重要，但人们对其了解甚少。关于无离子表面层的标准图景与强离子特异性行为之间长期存在争议，后者在许多情况下表明简单无机离子对界面有显著倾向。在此，我们提出了一个关于含单价无机离子的水性电解质气/液界面结构的统一且一致的观点。分子动力学计算表明，在盐溶液和碱中，带正电荷的离子，如碱金属阳离子，会被界面排斥，而阴离子，如卤化物或氢氧根离子，表现出不同的表面倾向，主要与离子极化率和大小相关。由于水合氢离子对气/液界面有显著倾向，酸的行为有所不同。因此，阳离子和阴离子在表面都表现出浓度增加，结果这些酸（与碱和盐不同）降低了水的表面张力。模拟结果得到了表面选择性非线性振动光谱的支持，该光谱揭示了除其他外水合氢离子存在于气/液界面。离子对气/液界面的特异性倾向对一系列非均相物理和化学过程具有重要意义，包括气溶胶的大气化学、腐蚀过程和气泡聚并。
