Temperature-induced micelle to vesicle transition in the sodium dodecylsulfate/dodecyltriethylammonium bromide system.
Temperature-induced micelle to vesicle transition in the sodium dodecylsulfate/dodecyltriethylammonium bromide system.
复制标题
DOI：
10.1002/anie.200350913
复制
发表时间：
2003-05
影响因子：
--
通讯作者：
Haiqing Yin;Zukang Zhou;Jianbin Huang;Rong Zheng;Yongyi Zhang
中科院分区：
文献类型：
--
作者：
Haiqing Yin;Zukang Zhou;Jianbin Huang;Rong Zheng;Yongyi Zhang
2188 2003 Wiley-VCH Verlag GmbH & Co. KGaA，魏因海姆DOI：10.1002/anie. 200350913 Angew. Chem.Int.Ed.2003，42，2188-2191中所述的温度升高时从有序态到无序态的转变[3]或从更高有序态到更低有序态的转变（例如从囊泡到胶束的转变[4]）通常发生在有序的组装体中。然而，到目前为止，对温度诱导的反向转变，如胶束到囊泡转变（MVT）的研究还很少见。本文首次报道了温度诱导的阳离子-阴离子表面活性剂体系的MVT。以2：1的摩尔比制备十二烷基硫酸钠（SDS）/十二烷基三乙基溴化铵（DEAB）体系，总浓度（Ctotal）为10 mM。浊度测量结果显示在图1a中。随着温度从30 ℃升高到508 ℃，观察到浊度明显增加，这表明系统中聚集体的生长。在转变过程中没有观察到相分离或沉淀，这与在一些离子表面活性剂体系中观察到的“浊点”现象不同。[5]动态光散射（DLS）研究，冷冻断裂技术与电子显微镜（FF-EM）观察，和流变学测量被用来研究系统中的温度诱导转变。208 C下，聚集体的平均流体动力学半径（hRhi）为25 nm（图2a）。稳态流动曲线（图3）揭示了系统的非牛顿性质，因此表明存在不对称聚集体。在流动曲线上也表现出明显的剪切增稠特征。已经有充分的文献证明[6]，圆柱形胶束的生长或流动排列是稀表面活性剂溶液中剪切增稠行为的原因。然而，通过FF-EM也观察到一些小的球形囊泡（图4a）。因此，我们可以得出结论，圆柱形胶束是主要的聚集体，共存的一些小的球形囊泡在系统中。在258 ℃下从DLS（图2b）和流变曲线获得了类似的结果，这表明在20 ℃和258 ℃之间没有明显的变化。然而，当温度上升到308 ℃时，情况就不同了。DLS图（图2 c）显示，与小聚集体（Rh <25 nm）对应的峰相对于258 ℃时的峰收缩，而另一个峰出现（Rh <100 nm）。多分散性指数（PI，通过累积量方法计算）从0.282（258 ℃）增长到0.339（308 ℃），这表明系统中囊泡/胶束比率的增加。[7]通过FF-TEM观察到直径为150-200 nm的囊泡（图4 b），这与DLS图中新出现的峰一致。而且
2188 2003 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim DOI: 10.1002/anie. 200350913 Angew. Chem. Int. Ed. 2003, 42, 2188–2191 transition from an ordered state to a disordered one [3] or from a higher ordered state to a lower ordered one (such as the transition from a vesicle to a micelle [4]) on increasing the temperature usually occurs among organized assemblies. However, studies of the reverse temperature-induced transitions, such as micelle to vesicle transition (MVT), are so far rare. Herein, we report for the first time a temperatureinduced MVT in a cationic–anionic surfactant system. The sodium dodecylsulfate (SDS)/dodecyltriethylammonium bromide (DEAB) system was prepared in a molar ratio of 2: 1 and a total concentration (Ctotal) of 10 mm. The results of the turbidity measurements are shown in Figure 1 a. A clear increase in turbidity was observed as the temperature increased from 30 to 508C, which suggests the growth of aggregates in the system. No phase separation or precipitate was observed during the transition, which is different from the “cloud point” phenomena seen in some ionic surfactant systems.[5]Dynamic light scattering (DLS) studies, a freeze fracture technique with observation by electron microscopy (FF-EM), and rheology measurements were used to investigate the temperature-induced transition in the system. The aggregate has an average hydrodynamic radius (hRhi) of 25 nm at 208C (Figure 2 a). A steady flow curve (Figure 3) revealed the non-Newtonian nature of the system and thus indicated the existence of asymmetric aggregates. A remarkable shearthickening feature was also evident in the flow curve. It has been well documented [6] that the growth or flow alignment of cylindrical micelles was responsible for the shear-thickening behavior in dilute surfactant solutions. However, a few small spherical vesicles were also observed by FF-EM (Figure 4a). Thus, we can conclude that cylindrical micelles are the major aggregates which coexist with a few small spherical vesicles in the system. Similar results were obtained at 258C from DLS (Figure 2b) and rheology curves, which indicate there was no apparent change between 20 and 258C. However, the situation became different as the temperature increased to 308C. A DLS plot (Figure 2 c) showed that the peak corresponding to the small aggregates (Rh∼ 25 nm) shrank relative to that at 258C, while another peak appeared (Rh∼ 100 nm). The polydispersity index (PI, calculated by the Cumulant method) grew from 0.282 (258C) to 0.339 (308C), which was indicative of the increase in the vesicle/micelle ratio in the system.[7] Vesicles with a diameter of 150–200 nm were observed by FF-TEM (Figure 4b), which coincides with the newly appeared peak in the DLS plot. Moreover, there