Ono Yousuke, Kawasaki Hideya, Annaka Masahiko, Maeda Hiroshi
Department of Chemistry, Faculty of Science, Kyushu University, 33 Hakozaki, Higashi-ku, Fukuoka 812-8581, Japan.
J Colloid Interface Sci. 2005 Jul 15;287(2):685-93. doi: 10.1016/j.jcis.2005.02.021.
Effects of micelle-to-vesicle transitions on the degree of counterion binding (beta) were investigated on three systems. For the concentration-dependent micelle-to-vesicle transition in the didodecyldimethylammonium bromide (DDAB)/water system, in the region of coexistent micelles and vesicles, less than 3 mM, the beta values increased significantly with DDAB concentration: beta (0.07 mM)=0.35 and beta (3 mM)=0.93. In the coexistent region, activities of the bromide ion, a(Br), were almost independent of the DDAB concentration, suggesting the pseudo-phase nature of both micelles and vesicles. In the concentration-dependent vesicle-to-lamellar transition region above 5 mM, where multilamellar vesicles were prevailing, on the other hand, the beta values were only little affected by this transition. This suggests that the increase in the layer number of DDAB multilamellar vesicles scarcely affects the beta values. This was also supported by the fact that the destruction of multilamellar vesicles by ultrasonication did not change the beta values. These results strongly suggest that the inner and outer monolayers of DDAB multilamellar vesicles are characterized by similar beta values. The second system, cetyltrimethylammonium bromide (CTAB)/DDAB mixtures, showed composition-dependent transitions depending on the mole fraction of DDAB X(DDAB): spherical micelles (0<X(DDAB)<0.2)-->rodlike micelles (0.2<X(DDAB)<0.4)-->vesicles (0.6<X(DDAB)<1). Values of beta increased with both the sphere-to-rodlike micelle transition and the micelle-to-vesicle transition. The increase in the beta value was larger for the latter than for the former transition. Little effects of ultrasonication on beta was also observed for the multilamellar vesicles of CTAB/DDAB mixtures. In the third system of the mixtures of two single chain surfactants, protonated and non-protonated of oleyldimethylamine oxide, the dependence of beta on the degree of ionization (alpha) can be well described with a theoretical curve, derived on the basis of the linear relation between the surface charge density and the alpha value, despite the occurrence of the micelle-to-vesicle transition.
在三个体系中研究了胶束到囊泡转变对反离子结合程度（β）的影响。对于十二烷基二甲基溴化铵（DDAB）/水体系中浓度依赖性的胶束到囊泡转变，在共存胶束和囊泡的区域，即浓度低于3 mM时，β值随DDAB浓度显著增加：β（0.07 mM） = 0.35，β（3 mM） = 0.93。在共存区域，溴离子的活度a(Br)几乎与DDAB浓度无关，这表明胶束和囊泡都具有假相性质。另一方面，在浓度高于5 mM的浓度依赖性囊泡到层状转变区域，此时多层层状囊泡占主导，β值几乎不受此转变的影响。这表明DDAB多层层状囊泡层数的增加几乎不影响β值。超声处理破坏多层层状囊泡不会改变β值这一事实也支持了这一点。这些结果有力地表明，DDAB多层层状囊泡的内、外单层具有相似的β值。第二个体系，十六烷基三甲基溴化铵（CTAB）/DDAB混合物，根据DDAB的摩尔分数X(DDAB)表现出组成依赖性转变：球形胶束（0 < X(DDAB) < 0.2）→棒状胶束（0.2 < X(DDAB) < 0.4）→囊泡（0.6 < X(DDAB) < 1）。β值随着从球形胶束到棒状胶束的转变以及胶束到囊泡的转变而增加。后者导致的β值增加幅度大于前者。对于CTAB/DDAB混合物的多层层状囊泡，超声处理对β的影响也很小。在第三个体系，油基二甲基氧化胺的质子化和非质子化两种单链表面活性剂的混合物中，尽管发生了胶束到囊泡的转变，但基于表面电荷密度与α值之间的线性关系推导得到的理论曲线能够很好地描述β对电离度（α）的依赖性。
