Surface Tensions, Surface Potentials, and the Hofmeister Series of Electrolyte Solutions

Abstract

A theory is presented which allows us to accurately calculate the surface tensions and the surface potentials of electrolyte solutions. Both the ionic hydration and the polarizability are taken into account. We find a good correlation between the Jones-Dole viscosity B coefficient and the ionic hydration near the air-water interface. The kosmotropic anions such as fluoride, iodate, sulfate, and carbonate are found to be strongly hydrated and are repelled from the interface. The chaotropic anions such as perchlorate, iodide, chlorate, and bromide are found to be significantly adsorbed to the interface. Chloride and bromate anions become weakly hydrated in the interfacial region. The sequence of surface tensions and surface potentials is found to follow the Hofmeister ordering. The theory quantitatively accounts for the surface tensions of 10 sodium salts for which there is experimental data.

Long-range specific ion-ion interactions in hydrogen-bonded liquid films

“…However, since the interfacial I − and Br − profiles evaluated on these premises (Figure 4) qualitatively match those obtained by molecular dynamics calculations, 10 do not discriminate among different explanations of the mechanism of anion enrichment at air-liquid interfaces. 9,10,12,44 Since the average ion-ion separation r i − r j = 87 nm at 5 μM ( r i − r j /nm = 150 (c/μM) −1/3 ) exceeds the Bjerrum length (the interionic separation between two monovalent ions at which their mutual electrostatic energy equals the average thermal energy, k B T) 45 λ B = e 2 /(4πε 0 εk B T) = 0.7 or 56 nm in H 2 O (ε = 78) or vacuum (ε = 1), respectively, the expectation is that anions should behave independently of each other in < 5 μM solutions. However, this is clearly not the case.…”

Adsorption of cationic polyions onto a hydrophobic surface in the presence of Hofmeister salts

“…Unfortunately, the state of the art force fields for atomistic simulations lead to too much adsorption of chaotropic ions, resulting in surface tensions which deviate strongly from the experimental measurements [17,35]. On the other hand, the effective potentials used in the present work result in a smaller adsorption and produce surface and interfacial tensions in excellent agreement with the experimental measurements [13,14,16]. This makes it difficult for us to compare our methodology with the classical atomistic simulations.…”

“…This is different from a conductor which leads to an ionelectrode attraction [42]. The approximate charge-image potential at a distance z from the interface was calculated to be [14] …”

Ion fluxes through nanopores and transmembrane channels

“…Such artifacts of classical water and ion models have been recently observed in the studies of ionic solvation near interfaces, when compared to the full ab initio simulations [23]. It has been shown that for ionic solvation in an interfacial geometry properly constructed dielectric continuum models agree better with results of full ab initio simulations than the classical explicit water models [23][24][25].…”