As tailorable solvents, the physiochemical properties of ionic liquids can be tuned by the structure of ions. Herein, we investigate the structural effects of ILs on the self-assembly of surfactants. It has been confirmed that the cationic surfactant 1-hexadecyl-3-methylimidazolium bromide (C₁₆mimBr) can self-assemble into micellar and lamellar lyotropic liquid crystal phases in the aprotic ionic liquid (AIL) 1-ethyl-3-methylimidazolium tetrafluoroborate ([Emim]BF₄). In this work, we explore the aggregation behaviours in AILs with different alkyl chains on the imidazolium group, i.e., 1-propyl-3-methylimidazolium tetrafluoroborate ([Pmim]BF₄), 1-butyl-3-methylimidazolium tetrafluoroborate ([Bmim]BF₄), 1-hexyl-3-methylimidazolium tetrafluoroborate ([Hmim]BF₄) and 1-octyl-3-methylimidazolium tetrafluoroborate ([Omim]BF₄). With the increase of the cation chain length, AILs have better solubility of the solvophobic part of the surfactants and hence a weaker driving force for self-assembly. Therefore, the critical micellization concentration of C₁₆mimBr in AILs increases as confirmed by the surface tension and small angle X-ray scattering characterizations. More interesting things happen to the phase behaviours. Besides the micellar and lamellar lyotropic liquid crystal phases, a hexagonal lyotropic liquid crystal phase is formed in [Pmim]BF₄ while hexagonal and bicontinuous cubic lyotropic liquid crystal phases are formed in [Bmim]BF₄, [Hmim]BF₄ and [Omim]BF₄. It is surprising to observe richer phase behaviours in solvents of lower cohesive energy. The detailed structural information of various aggregates has been obtained by small-angle X-ray scattering. It is demonstrated that AILs work as not only solvents but also co-surfactants.

中文翻译：

---

咪唑鎓表面活性剂在非质子离子液体中的自组装。2.比溶剂更多

作为可调节的溶剂，离子液体的物理化学性质可以通过离子的结构进行调整。在这里，我们研究表面活性剂对表面活性剂自组装的结构影响。已证实阳离子表面活性剂溴化1-十六烷基-3-甲基咪唑鎓（C ₁₆ mimBr）可以在非质子离子液体（AIL）1-乙基-3-甲基咪唑鎓四氟硼酸盐（ [Emim] BF ₄）。在这项工作中，我们探索在咪唑基团上具有不同烷基链的AIL中的聚集行为，即1-丙基-3-甲基咪唑四氟硼酸酯（[Pmim] BF ₄），1-丁基-3-甲基咪唑四氟硼酸酯（[Bmim]高炉₄），1-己基-3-甲基咪唑四氟硼酸酯（[Hmim] BF ₄）和1-辛基-3-甲基咪唑四氟硼酸酯（[Omim] BF ₄）。随着阳离子链长度的增加，AIL在表面活性剂的疏溶剂部分具有更好的溶解性，因此对自组装的驱动力更弱。因此，如表面张力和小角度X射线散射特征所证实的，AIL中C ₁₆ mimBr的临界胶束浓度增加。更有趣的事情发生在阶段行为上。除了胶束和层状溶致液晶相之外，在[Pmim] BF _4中还形成了六方溶致液晶相。在[Bmim] BF ₄，[Hmim] BF ₄和[Omim] BF ₄中形成六方和双连续立方溶致液晶相。令人惊讶的是，在较低内聚能的溶剂中观察到更丰富的相行为。各种聚集体的详细结构信息已通过小角度X射线散射获得。事实证明，AILs不仅可以作为溶剂，而且可以作为辅助表面活性剂。