Imanishi Kiyoe, Einaga Yoshiyuki
Department of Chemistry, Nara Women's University, Nara 630-8506, Japan.
J Phys Chem B. 2007 Jan 11;111(1):62-73. doi: 10.1021/jp065317l.
The wormlike micelles formed with the binary mixtures of surfactant polyoxyethylene alkyl ethers (CiEj), C10E5 + C14E5 (Mix1) and C14E5 + C14E7 (Mix2), were characterized by static (SLS) and dynamic light scattering (DLS) experiments. The SLS results have been analyzed with the aid of the light scattering theory for micelle solutions, thereby yielding the molar mass Mw(c) as a function of c along with the cross-sectional diameter d of the micelle. The observed Kc/DeltaR0 as a function of c, the mean-square radius of gyration (S2) and the hydrodynamic radius RH as functions of Mw have been well described by the theories for the wormlike spherocylinder model. It has been found that the micellar length increases with increasing concentration c or with raising temperature T irrespective of the composition of the surfactant mixtures. The length of the Mix1 and Mix2 micelles at fixed c and T steeply increases with increasing weight fraction wt of C14E5 in both of the surfactant mixtures, implying that the micelles greatly grow in length when the surfactant component with longer alkyl group or with shorter oxyethylene group increases in the mixture. The results are in line with the findings for the micelles of the single surfactant systems where the CiEj micelles grow in length to a greater extent for larger i and smaller j. Although the values of d and the spacing s between the adjacent surfactant molecules on the micellar surface do not significantly vary with composition of the surfactant mixture, the stiffness parameter lambda-1 remarkably decreases with wt in both Mix1 and Mix2 micelles, indicating that the stiffness of the micelle is controlled by the relative strength of the repulsive force due to the hydrophilic interactions between oxyethylene groups to the attractive one due to the hydrophobic interactions between alkyl groups among the surfactant molecules.
通过表面活性剂聚氧乙烯烷基醚（CiEj）的二元混合物形成的蠕虫状胶束，即C10E5 + C14E5（混合物1）和C14E5 + C14E7（混合物2），通过静态（SLS）和动态光散射（DLS）实验进行了表征。借助胶束溶液的光散射理论对SLS结果进行了分析，从而得出摩尔质量Mw(c)作为c的函数以及胶束的横截面直径d。对于蠕虫状球圆柱体模型的理论，已经很好地描述了观察到的Kc/DeltaR0作为c的函数、均方回转半径（S2）以及流体力学半径RH作为Mw的函数。已经发现，无论表面活性剂混合物的组成如何，胶束长度都随着浓度c的增加或温度T的升高而增加。在固定的c和T下，混合物1和混合物2胶束的长度随着两种表面活性剂混合物中C14E5重量分数wt的增加而急剧增加，这意味着当混合物中具有较长烷基或较短氧乙烯基团的表面活性剂成分增加时，胶束长度会大幅增长。这些结果与单一表面活性剂体系胶束的研究结果一致，即在单一表面活性剂体系中，对于较大的i和较小的j，CiEj胶束在长度上增长得更多。尽管胶束表面相邻表面活性剂分子之间的d值和间距s不会随表面活性剂混合物的组成而显著变化，但在混合物1和混合物2胶束中，刚度参数lambda-1都随着wt显著降低，这表明胶束的刚度由表面活性剂分子中氧乙烯基团之间的亲水相互作用产生的排斥力与烷基之间的疏水相互作用产生的吸引力的相对强度所控制。
