State Key Laboratory of Magnetic Resonance and Atomic and Molecular Physics, Wuhan Institute of Physics and Mathematics, Chinese Academy of Sciences, Wuhan 430071, P. R. China.
J Phys Chem B. 2010 Jun 17;114(23):7808-16. doi: 10.1021/jp101032z.
This article provides a full description of the mixed micelle formation process at a molecular level. The mechanism of mixed micelle formation in binary surfactant aqueous solution systems, ionic/nonionic mixed systems (12-2-12/TX-100, 14-2-14/TX-100, and SDS/TX-100), and ionic/ionic mixed systems (12-2-12/TTAB, 14-2-14/TTAB, and SDS/CTAB), in heavy water solutions was studied by (1)H NMR spectroscopy. The critical micellization concentrations of each individual component in the mixed surfactant solutions were gained by analyzing changes in chemical shift and intensities of resonance peaks. The chemical shift changes indicated that in the 12-2-12/TX-100 and SDS/TX-100 systems, micelles of TX-100 formed first, and then 12-2-12 or SDS molecules were fused in the micelles, respectively, which has been proved by 2D NOESY experiments. In contrast, 14-2-14 was the first component to form the micelles in the 14-2-14/TX-100 system. Although 12-2-12 and 14-2-14 are analogs and differ only in the length of the hydrophobic chain by two methylene groups, they showed different behaviors in the micellization processes in the mixture with TX-100. The observation suggests that in the binary surfactant system under current study, the component with lower cmc in the mixed solution aggregates first; then, the other one fuses, resulting in the mixed micelles as the total concentration increases. The same results were obtained for the ionic/ionic solutions, 12-2-12/TTAB, 14-2-14/TTAB, and SDS/CTAB. The above results suggest that the two mixed surfactants do not aggregate synchronously. It obviously demonstrates that the so-called "cmc of the mixed surfactant solution" needs reconsideration.
本文从分子水平上全面描述了混合胶束的形成过程。通过（1）H NMR 光谱研究了在重水溶液中双离子表面活性剂水溶液体系（12-2-12/TX-100、14-2-14/TX-100 和 SDS/TX-100）、离子/非离子混合体系（12-2-12/TTAB、14-2-14/TTAB 和 SDS/CTAB）中混合胶束形成的机制。通过分析共振峰的化学位移和强度的变化，得到了混合表面活性剂溶液中各组分的临界胶束浓度。化学位移的变化表明，在 12-2-12/TX-100 和 SDS/TX-100 体系中，TX-100 首先形成胶束，然后分别将 12-2-12 或 SDS 分子融合到胶束中，这一点已通过 2D-NOESY 实验得到证明。相比之下，14-2-14 是 14-2-14/TX-100 体系中第一个形成胶束的组分。尽管 12-2-12 和 14-2-14 是类似物，只是疏水链长相差两个亚甲基，但它们在与 TX-100 的混合物中胶束化过程中表现出不同的行为。这一观察结果表明，在当前研究的二元表面活性剂体系中，混合溶液中 cmc 较低的组分首先聚集；然后，随着总浓度的增加，另一个组分融合，形成混合胶束。对于离子/离子溶液 12-2-12/TTAB、14-2-14/TTAB 和 SDS/CTAB，也得到了相同的结果。上述结果表明，两种混合表面活性剂不会同步聚集。这显然表明所谓的“混合表面活性剂溶液的 cmc”需要重新考虑。
