Institut Européen de Chimie et Biologie, UMR 5248 CBMN, CNRS-Université de Bordeaux-ENITAB, 2 rue Robert Escarpit, F-33607 Pessac, France.
Langmuir. 2010 Jul 6;26(13):10645-56. doi: 10.1021/la1008768.
The effect of counterions was investigated and analyzed to probe the principal ionic effects influencing the micellization behavior of dimeric cationic surfactant ethanediylbis(dimethyltetradecylammonium), referred to as gemini 14-2-14. The 30 counterions were classified to four different families depending on their nature: (1) small and inorganic counterions which are typically taken from the Hofmeister series were studied to focus on the effect of ion type; (2) n-alkyl carboxylate counterions were studied to focus on the effect of the hydrophobicity of counterions; (3) aromatic carboxylate counterions were included to focus on the effect of the position of substitutions; and (4) other counterions were included in order to shed light on other parameters. By investigating the critical micelle concentration (CMC), ionization degree of micelle (alpha), free energy of micellization (DeltaG(M)), and aggregation numbers N of the gemini surfactant with these different types of anions, we demonstrated the effect of different ion properties independently. This approach allowed us to describe the effect of counterions on the micellization behavior of the gemini surfactant in terms of complex interplay between hydrophobicity of anions and other ion properties such as counterion hydration, interfacial packing of ions, and ionic morphology. Indeed, our results clearly demonstrate that a counterion effect on micellization properties cannot be described as a result of one single parameter of ions, as is too often assumed, but rather the balancing effects cooperatively affect the propensity of counterions to form ion pairs with surfactant headgroups and the entropy gain upon micellization. These results provide new insight in understanding the effect of ions on the delicate balance of forces controlling aggregate morphology and solution properties of charged amphiphilic molecules.
反离子的影响被研究和分析，以探讨影响二聚阳离子表面活性剂乙二基双（二甲基十四烷基）铵（称为双子 14-2-14）胶束化行为的主要离子效应。根据性质，将 30 种反离子分为四大类：（1）通常来自 Hofmeister 序列的小无机反离子，以研究离子类型的影响；（2）研究 n-烷基羧酸盐反离子，以研究反离子疏水性的影响；（3）包括芳香族羧酸盐反离子，以研究取代位置的影响；（4）包括其他反离子，以了解其他参数的影响。通过研究不同类型阴离子对双子表面活性剂的临界胶束浓度（CMC）、胶束电离度（α）、胶束化自由能（ΔG（M））和聚集数 N，我们独立研究了不同离子性质的影响。这种方法使我们能够根据阴离子疏水性和其他离子性质（如反离子水化、离子界面排列和离子形态）之间的复杂相互作用，描述反离子对双子表面活性剂胶束化行为的影响。事实上，我们的结果清楚地表明，反离子对胶束化性质的影响不能仅仅归因于离子的单一参数，就像人们经常假设的那样，而是平衡效应共同影响反离子与表面活性剂头基形成离子对的倾向以及胶束化时的熵增益。这些结果为理解离子对控制带电两亲分子聚集形态和溶液性质的微妙平衡的影响提供了新的认识。
