Department of Physical Chemistry, Sofia University, Bulgaria.
J Colloid Interface Sci. 2012 Dec 1;387(1):234-43. doi: 10.1016/j.jcis.2012.07.020. Epub 2012 Jul 20.
The surface tension σ of inorganic electrolyte aqueous solutions at a given concentration c follows the Hofmeister series. The explanation of this phenomenon was sought in the increased adsorption of certain ions due to specific ion-surface interactions. However, the ion-specific dependence of the activity coefficient γ(±) on c also influences σ, and its contribution to the ion-specificity of σ prevails. Thus, the surface tension of potassium salts follows the order σ(KOH)>σ(KCl)>σ(KNO3), which turns out to be a direct corollary of the corresponding activity coefficients series: γ(KOH)>γ(KCl)>γ(KNO3). In fact, the adsorption of NO(3)(-) at the water surface is lower than that of OH(-) and Cl(-)! If the bulk ion-specific effects are correctly evaluated, Schmutzer's classical model predicts accurately the surface tension of a large number of inorganic salt solutions in a wide concentration range, without adjustable parameters. This model accounts for image and hydration forces. Comparison with tensiometric data shows that other ion-surface interactions play a role only in the adsorption of ions of bare radius larger than a threshold value of about 1.95 Å (e.g. HCOO(-), I(-), SCN(-)).
在给定浓度 c 下，无机电解质水溶液的表面张力 σ 遵循豪夫迈斯特序列。人们试图从特定的离子-表面相互作用导致某些离子的吸附增加来解释这一现象。然而，离子特性对活度系数 γ(±) 对 c 的依赖性也会影响 σ，其对 σ 的离子特性的贡献占主导地位。因此，钾盐的表面张力遵循 σ(KOH)>σ(KCl)>σ(KNO3)的顺序，这实际上是相应活度系数系列的直接推论：γ(KOH)>γ(KCl)>γ(KNO3)。事实上，NO3(-)在水表面的吸附低于 OH(-)和 Cl(-)！如果正确评估了体相离子特性的影响，施穆策尔的经典模型可以在没有可调参数的情况下，准确地预测大量无机盐溶液在很宽浓度范围内的表面张力。该模型考虑了离子的图像力和水合力。与表面张力数据的比较表明，只有离子半径大于约 1.95 Å 的裸离子（如 HCOO(-)、I(-)、SCN(-)）的吸附才会产生其他离子-表面相互作用。
