Lam Minh T, Adamson William D, Miao Shurui, Atkin Rob, Warr Gregory G
School of Chemistry and University of Sydney Nano Institute, The University of Sydney, NSW 2006, Australia.
School of Molecular Sciences, The University of Western Australia, WA 6009, Australia.
J Colloid Interface Sci. 2019 Sep 15;552:597-603. doi: 10.1016/j.jcis.2019.05.082. Epub 2019 May 25.
The high CMCs and low aggregation numbers of ionic micelles in the extreme electrolyte environment of ionic liquids (ILs) seem to be at odds with the effect of dilute aqueous electrolytes, which lower CMCs and promote elongated micelles. We hypothesise that the driving force for micellisation in ILs is determined by their underlying amphiphilic nanostructure, and that this can be controlled by mixing with water.
CMCs and micelle sizes of dodecyltrimethylammonium bromide (DTAB) are determined in mixed solvents comprising water and the ionic liquids ethylammonium nitrate (EAN), ethanolammonium nitrate (EtAN), and propylammonium nitrate (PAN) over a wide composition range. Their behaviour is compared with aqueous electrolytes up to their solubility limit. CMCs are determined by a variety of techniques, and their relative strengths critically evaluated. Micelle morphology is determined by small-angle neutron scattering.
In water-rich mixtures, ILs do behave like simple electrolytes. Counterion binding dominates, both lowering the aqueous CMC and favouring a sphere-rod transition. However, even at modest concentrations, IL cations become incorporated into the micelle, causing the CMC to pass through a minimum, and arresting the sphere-rod transition. The efficiency of the cation depends on its amphiphilicity. As the IL content increases further, its role as a component of the bulk solvent becomes dominant: Only here does IL nanostructure influence micellization, as it increases alkyl chain solubility (EAN, PAN) and hence raises the CMC.
在离子液体（ILs）的极端电解质环境中，离子胶束的临界胶束浓度（CMCs）高且聚集数低，这似乎与稀水电解质的作用相悖，稀水电解质会降低CMC并促进胶束伸长。我们假设在离子液体中胶束形成的驱动力由其潜在的两亲纳米结构决定，并且这可以通过与水混合来控制。
在包含水和离子液体硝酸乙铵（EAN）、硝酸乙醇铵（EtAN）和硝酸丙铵（PAN）的混合溶剂中，在很宽的组成范围内测定了十二烷基三甲基溴化铵（DTAB）的CMC和胶束大小。将它们的行为与达到其溶解度极限的水电解质进行比较。通过多种技术测定CMC，并对它们的相对强度进行严格评估。通过小角中子散射确定胶束形态。
在富水混合物中，离子液体的行为确实类似于简单电解质。反离子结合起主导作用，既降低了水相中的CMC，又有利于球形 - 棒状转变。然而，即使在适度浓度下，离子液体阳离子也会掺入胶束中，导致CMC经过一个最小值，并阻止球形 - 棒状转变。阳离子的效率取决于其两亲性。随着离子液体含量进一步增加，其作为本体溶剂组分的作用变得占主导：只有在这里离子液体纳米结构才会影响胶束化，因为它增加了烷基链的溶解度（EAN，PAN），从而提高了CMC。
