Comparison of Vesicle Formation in Zwitanionic and Catanionic Mixtures of Hydrocarbon and Fluorocarbon Surfactants: Phase Behavior and Structural Progression
Comparison of Vesicle Formation in Zwitanionic and Catanionic Mixtures of Hydrocarbon and Fluorocarbon Surfactants: Phase Behavior and Structural Progression
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DOI：
10.1021/la901191a
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发表时间：
2009-10-06
期刊：
影响因子：
3.9
通讯作者：
Gradzielski, Michael
中科院分区：
文献类型：
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作者：
Wolf, Christian;Bressel, Katharina;Gradzielski, Michael
研究了全氟表面活性剂与烃类表面活性剂的两性-阴离子和阴阳离子混合物的相行为，其中全氟辛酸锂（LiPFO）为阴离子表面活性剂，十四烷基二甲基氧化胺（TDMAO）为两性离子表面活性剂，十四烷基三甲基溴化铵（TTAB）为阳离子表面活性剂。样品作为混合比的函数，其特征在于通过电导率，光散射，低温TEM，和流变学。尽管两性离子表面活性剂和阳离子表面活性剂的链长相等，但我们观察到在这些系统中存在很大不同的相行为，其中阴阳离子系统在等摩尔混合周围形成沉淀物，而两性阴离子系统没有观察到这种沉淀。这一要求可以根据两性阴离子体系的低得多的相互作用参数β（来自cmc测量）来合理化。因此，在两性阴离子混合物中，观察到更大范围的稳定单层囊泡，而对于阴阳离子系统，存在更大的囊泡，具有更强的形成多层囊泡的趋势。另一个有趣的效果是，仅对于两性阴离子混合物的情况，在形成囊泡之前观察到粘度的显著增加，这意味着此处从球形胶束到囊泡的转变通过强不等轴胶束聚集体发生，这在阴阳离子混合物的情况下没有观察到。从这些结果可以得出结论，在这些混合物中形成的囊泡的结构和稳定性在很大程度上由允许相应地修饰的静电相互作用的程度控制。
The phase behavior of zwitanionic and catanionic mixtures of perfluoro and hydrocarbon surfactants has been Studied for the case of lithium perfluorooctanoate (LiPFO) as anionic surfactant and tetradecyldimethylamine oxide (TDMAO) as zwitterionic or tetradecyltrimethyl ammonium bromide (TTAB) as cationic surfactant. Samples as a function of the mixing ratio were characterized by means of electric conductivity, light scattering, cryo-TEM, and rheology. Despite the equal chain length of the zwitterionic and cationic surfactant we observe largely different phase behavior in these systems with the formation of precipitates around equimolar mixing for the catanionic system, while no such precipitation is observed for the zwitanionic system. This call be rationalized in terms of the much lower interaction parameter beta (from cmc measurements) fort lie case of the zwitanionic system. Accordingly, in the zwitanionic mixture a larger range of stable unilamellar vesicles is observed, while for the catanionic system larger vesicles are present,with a much stronger tendency for formation of multilamellar vesicles, Another interesting effect is that only for the case of the zwitanionic mixture a substantial increase of viscosity is observed prior to the formation of vesicles, which means that here the transition from spherical micelles to vesicles takes place via strongly anisometric micellar aggregates, which are not observed for the case of the catanionic mixtures. From these results it can be concluded that the structure and stability of vesicles formed in these mixtures are largely controlled by the extent of the electrostatic interactions which allows modification accordingly.