Yalcin Dilek, Drummond Calum J, Greaves Tamar L
School of Science, College of Science, Engineering and Health, RMIT University, GPO Box 2476, Melbourne, Victoria 3001, Australia.
Soft Matter. 2020 Oct 28;16(41):9456-9470. doi: 10.1039/d0sm01298j.
Protic ionic liquids (PILs) are the largest and most tailorable known class of non-aqueous solvents which possess the ability to support amphiphile self-assembly. However, little is known about the effect of solvent additives on this ability. In this study, the lyotropic liquid crystal phase (LLCP) behavior of the cationic surfactant cetyltrimethylammonium bromide (CTAB) was investigated in the model PILs of ethylammonium nitrate (EAN) and ethanolammonium nitrate (EtAN), and derived multi-component solvent systems containing them to determine phase formation and diversity with changing solvent composition. The solvent systems were composed of water, nitric acid and ethylamine (or ethanolamine), with 26 unique compositions for each PIL covering the apparent pH and ionicity ranges of 0-13.5 and 0-11 M, respectively. The LLCPs were studied using cross polarized optical microscopy (CPOM) and small and wide-angle X-ray scattering (SAXS/WAXS). Partial phase diagrams were constructed for CTAB concentrations of 50 wt% and 70 wt% in the temperature range of 25 °C to 75 °C to characterise the effect of surfactant concentration and temperature on the LLCPs in each solvent environment. Normal micellar (L1), hexagonal (H1) and bicontinuous cubic (V1) phases were identified at both surfactant concentrations, and from temperatures as low as 35 °C, with large variations dependent on the solvent composition. The thermal stability and diversity of phases were greater and broader in solvent compositions with excess precursor amines present compared to those in the neat PILs. In acid-rich solvent combinations, the same phase diversity was found, though with reduced onset temperatures of phase formation; however, some structural changes were observed which were attributed to oxidation/decomposition of CTAB in a nitric acid environment. This study showed that the ability of PIL solutions to support amphiphile self-assembly can readily be tuned, and that the ability of PILs to promote amphiphile self-assembly is robust, even with other solvent species present.
质子离子液体（PILs）是已知的最大且最具可定制性的非水溶剂类别，具有支持两亲分子自组装的能力。然而，关于溶剂添加剂对这种能力的影响却知之甚少。在本研究中，研究了阳离子表面活性剂十六烷基三甲基溴化铵（CTAB）在硝酸乙铵（EAN）和硝酸乙醇铵（EtAN）的模型质子离子液体以及包含它们的衍生多组分溶剂体系中的溶致液晶相（LLCP）行为，以确定随着溶剂组成变化的相形成和多样性。溶剂体系由水、硝酸和乙胺（或乙醇胺）组成，每种质子离子液体有26种独特的组成，分别覆盖0 - 13.5的表观pH范围和0 - 11 M的离子强度范围。使用交叉偏振光学显微镜（CPOM）以及小角和广角X射线散射（SAXS/WAXS）研究了溶致液晶相。构建了在25℃至75℃温度范围内CTAB浓度为50 wt%和70 wt%时的部分相图，以表征表面活性剂浓度和温度对每种溶剂环境中溶致液晶相的影响。在两种表面活性剂浓度下，均识别出了正常胶束（L1）、六方（H1）和双连续立方（V1）相，且从低至35℃的温度开始就有这些相，其变化很大程度上取决于溶剂组成。与纯质子离子液体相比，存在过量前体胺的溶剂组成中相的热稳定性和多样性更高且更广泛。在富酸溶剂组合中，发现了相同的相多样性，尽管相形成的起始温度有所降低；然而，观察到了一些结构变化，这归因于CTAB在硝酸环境中的氧化/分解。这项研究表明，质子离子液体溶液支持两亲分子自组装的能力可以很容易地调节，并且即使存在其他溶剂种类，质子离子液体促进两亲分子自组装的能力仍然很强。
