Gao HongChang, Zhu RongXian, Yang XiaoYan, Mao ShiZhen, Zhao Sui, Yu JiaYong, Du YouRu
State Key Laboratory of Magnetic Resonance and Atomic and Molecular Physics, Wuhan Institute of Physics and Mathematics, Chinese Academy of Sciences, Wuhan 430071, People's Republic of China.
J Colloid Interface Sci. 2004 May 15;273(2):626-31. doi: 10.1016/j.jcis.2003.12.047.
NMR self-diffusion coefficient measurements have been used to study the properties of polyethylene glycol (23) lauryl ether (Brij-35) with cetyltrimethylammonium bromide (CTAB) in the mixed aqueous solutions with different mole fractions of CTAB. By fitting the self-diffusion coefficients to the two-state exchange model, the critical micelle concentrations of the two solutes in the mixed solutions (cmc1 and cmc2) were obtained. The critical mixed micelle concentrations (cmc*) were then evaluated by the sum of cmc1 and cmc2, which are in good agreement with the results measured by the surface tension method. The cmc* values are lower than those of the ideal case of mixing, which indicates that the behavior of the CTAB/Brij-35 system is nonideal. Moderate interactions between CTAB and Brij-35 in their mixtures can be deduced from the interaction parameters (betaM) based on the cmc* obtained by the NMR self-diffusion method. The compositions (x1) of the mixed micelles at different total surfactant concentrations were also evaluated. By using these results, a possible mechanism of mixed micellar formation and a picture of the formation of nonsimultaneous CTAB/Brij-35 binary mixed micelle were proposed. In contrast to the case of CTAB/TX-100 system, Brij-35 molecules have a tendency to form micelles first at any mole fraction of CTAB. The mixed micellar self-diffusion coefficients (Dm) increase slightly at lower CTAB molar ratios, and then speed up with increasing CTAB mole fraction.
核磁共振自扩散系数测量已被用于研究聚乙二醇（23）月桂醚（Brij - 35）与十六烷基三甲基溴化铵（CTAB）在具有不同摩尔分数CTAB的混合水溶液中的性质。通过将自扩散系数拟合到双态交换模型，得到了混合溶液中两种溶质的临界胶束浓度（cmc1和cmc2）。然后通过cmc1与cmc2之和评估临界混合胶束浓度（cmc*），其与表面张力法测量的结果高度吻合。cmc值低于理想混合情况下的值，这表明CTAB/Brij - 35体系的行为是非理想的。基于通过核磁共振自扩散法获得的cmc，从相互作用参数（βM）可以推断出CTAB和Brij - 35在其混合物中的适度相互作用。还评估了不同总表面活性剂浓度下混合胶束的组成（x1）。利用这些结果，提出了混合胶束形成的可能机制以及非同时形成CTAB/Brij - 35二元混合胶束的图景。与CTAB/TX - 100体系的情况相反，在任何CTAB摩尔分数下，Brij - 35分子都倾向于首先形成胶束。混合胶束自扩散系数（Dm）在较低CTAB摩尔比时略有增加，然后随着CTAB摩尔分数的增加而加快。
