Bryant Saffron J, Atkin Rob, Gradzielski Michael, Warr Gregory G
School of Chemistry and Sydney Nano Institute, The University of Sydney, Sydney, NSW 2006, Australia.
School of Molecular Sciences, University of Western Australia, Crawley, WA 6009, Australia.
J Phys Chem Lett. 2020 Aug 6;11(15):5926-5931. doi: 10.1021/acs.jpclett.0c01608. Epub 2020 Jul 13.
Mixing of cationic and anionic surfactants in water can result in pseudo-double-tailed catanionic surfactant ion pairs that form lamellar phases or vesicles that are unstable toward electrolyte addition. Here we show that despite the very high ionic strengths, catanionic surfactants counterintuitively form a wider variety of self-assembled aggregates in pure ionic liquids (ILs, pure salts in a liquid phase) than in water, including micelles, vesicles, and lyotropic phases. Self-assembled structures only form when the IL is sufficiently polar to drive self-assembly through electrostatic interactions and/or H-bond networks, but the catanionic effect is manifested only when the IL does not itself exhibit pronounced amphiphilic nanostructure. This enables the type of catanionic aggregate formed to be designed by changing the hydrogen bonds between the ions through variation of the structures of the cation and anion. These results reveal an entirely new way of controlling catanionic surfactant self-assembly under nonaqueous and high-salt conditions.
阳离子表面活性剂和阴离子表面活性剂在水中混合可形成假双尾阴阳离子表面活性剂离子对，进而形成层状相或囊泡，但这些结构对添加电解质不稳定。我们在此表明，尽管离子强度极高，但与在水中相比，阴阳离子表面活性剂在纯离子液体（离子液体，处于液相的纯盐）中反而能形成种类更多的自组装聚集体，包括胶束、囊泡和溶致相。只有当离子液体具有足够的极性，能够通过静电相互作用和/或氢键网络驱动自组装时，自组装结构才会形成，但阴阳离子效应仅在离子液体本身不呈现明显两亲性纳米结构时才会显现。这使得通过改变阳离子和阴离子的结构来改变离子之间的氢键，从而设计出所形成的阴阳离子聚集体的类型成为可能。这些结果揭示了一种在非水和高盐条件下控制阴阳离子表面活性剂自组装的全新方法。
