Ávila Jocasta, Lozano-Martín Daniel, Simões Santos Mirella, Zhang Yunxiao, Li Hua, Pádua Agilio, Atkin Rob, Costa Gomes Margarida
Laboratoire de Chimie ENS Lyon, CNRS and Université de Lyon, 46 allée d'Italie, 69364 Lyon, France.
Grupo de Termodinámica y Calibración (TERMOCAL), Research Institute on Bioeconomy, Escuela de Ingenierías Industriales, Universidad de Valladolid, Paseo del Cauce, 59, 47011, Valladolid, Spain.
Phys Chem Chem Phys. 2023 Mar 1;25(9):6808-6816. doi: 10.1039/d2cp05145a.
Surface active ionic liquids (SAILs) combine useful characteristics of both ionic liquids (ILs) and surfactants, hence are promising candidates for a wide range of applications. However, the effect of SAIL ionic structures on their physicochemical properties remains unclear, which limits their uptake. To address this knowledge gap, in this work we investigated the density, viscosity, surface tension, and corresponding critical micelle concentration in water, as well as gas absorption of SAILs with a variety of cation and anion structures. SAILs containing anions with linear alkyl chains have smaller molar volumes than those with branched alkyl chains, because linear alkyl chains are interdigitated to a greater extent, leading to more compact packing. This interdigitation also results in SAILs being about two orders of magnitude more viscous than comparable conventional ILs. SAILs at the liquid-air interface orient alkyl chains towards the air, leading to low surface tensions closer to -alkanes than conventional ILs. Critical temperatures of about 900 K could be estimated for all SAILs from their surface tensions. When dissolved in water, SAILs adsorb at the liquid-air interface and lower the surface tension, like conventional surfactants in water, after which micelles form. Molecular simulations show that the micelles are spherical and that lower critical micelle concentrations correspond to the formation of aggregates with a larger number of ion pairs. CO and N absorption capacities are examined and we conclude that ionic liquids with larger non-polar domains absorb larger quantities of both gases.
表面活性离子液体（SAILs）兼具离子液体（ILs）和表面活性剂的有用特性，因此是众多应用的有望候选物。然而，SAILs的离子结构对其物理化学性质的影响仍不明确，这限制了它们的应用。为填补这一知识空白，在本工作中，我们研究了具有各种阳离子和阴离子结构的SAILs在水中的密度、粘度、表面张力及相应的临界胶束浓度，以及气体吸收情况。含有直链烷基链阴离子的SAILs的摩尔体积比含有支链烷基链阴离子的SAILs小，因为直链烷基链的相互穿插程度更高，导致堆积更紧密。这种相互穿插还使得SAILs的粘度比类似的传统离子液体大两个数量级左右。SAILs在液 - 气界面处使烷基链朝向空气，导致其表面张力比传统离子液体更低，更接近烷烃。根据SAILs的表面张力可估算出其临界温度约为900K。当溶解在水中时，SAILs像水中的传统表面活性剂一样吸附在液 - 气界面并降低表面张力，之后形成胶束。分子模拟表明胶束是球形的，且较低的临界胶束浓度对应于形成具有更多离子对的聚集体。我们研究了CO和N的吸收能力，得出具有较大非极性域的离子液体吸收这两种气体的量更大的结论。
