This communication represents the chemical alternative to the previous two papers dealing with the influence of positively charged alkali cations on the adsorption properties of the series of the standard surfactant system of alkali-perfluorocarbon octanoates. Now, this contribution describes the adsorption properties of the negatively charged cationic surfactant series of trimethyldodecyl-ammonium halides. In our latest contributions, we have put forward a new model of adsorption of ionic surfactants. It says that the surface excess of the adsorbed anionic surfactant is exclusively determined by the cross-sectional area of the positive counterion. This, however, has been demonstrated by applying relevant, positively charged (alkali) counterions only, i.e., by anionic surfactants. In this article, we extend the new model to negatively charged counterions (halides) applying the cationic standard surfactant series of the trimethyldodecylammonium-halides. A big difference between the hydration behavior of the positively charged alkali and the negatively charged counterions has become striking. Thus, for example, whereas the ratio between the naked ion radius of the cesium and of the lithium cation is almost 2-fold, it is practically equal for the chloride and the iodide anion. Surprisingly, however, the relevant adsorption data are practically identical. This means that the bigger, negatively charged halide counterions interact considerably more strongly with their residual ionic surfactant group than the positively charged alkali cations with theirs. Due to this, the size of the hydrated negative halide ions is considerably greater than that of the relevant positive alkali ions. These specialties can well be explained by the Stern model of charge distribution across a naked ion’s surface. It shows that for the electrostatic interaction between counterion and ionic surfactant headgroup, the peculiarities of the polar solvent of water will play a crucial role, too. By these investigations our new model of adsorption of ionic amphiphiles is further extended and gives finally evidence that it is of general validity.

中文翻译：

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反离子在离子两亲物在流体界面吸附中的作用


该通讯代表了前两篇论文的化学替代品，这些论文涉及带正电荷的碱阳离子对碱全氟化碳辛酸酯标准表面活性剂系列吸附性能的影响。现在，本文描述了带负电荷的阳离子表面活性剂系列三甲基十二烷基-卤化铵的吸附特性。在我们最新的贡献中，我们提出了一种离子表面活性剂吸附的新模型。它说吸附的阴离子表面活性剂的表面过量完全由正反离子的横截面积决定。然而，这已经通过仅应用相关的带正电（碱）的反离子，即阴离子表面活性剂来证明。在本文中，我们将新模型扩展到带负电荷的反离子（卤化物），应用三甲基十二氯铵卤化物的阳离子标准表面活性剂系列。带正电的碱和带负电的反离子之间的水合行为之间的巨大差异已经变得显着。因此，例如，虽然铯和锂阳离子的裸离子半径之比几乎是 2 倍，但氯化物和碘化物阴离子的比值实际上相等。然而，令人惊讶的是，相关的吸附数据几乎相同。这意味着较大的带负电荷的卤化物反离子与其残留的离子表面活性剂基团的相互作用比带正电荷的碱阳离子与其离子表面活性剂基团的相互作用要强得多。因此，水合负卤离子的大小远大于相关正碱离子的大小。 这些特性可以用裸离子表面电荷分布的 Stern 模型来很好地解释。结果表明，对于反离子和离子表面活性剂头基之间的静电相互作用，水的极性溶剂的特性也将起关键作用。通过这些研究，我们进一步扩展了离子两亲物吸附的新模型，并最终证明了它具有普遍的有效性。