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首页> 外文期刊>Langmuir: The ACS Journal of Surfaces and Colloids >Ionic Liquid Films at the Water-Air Interface: Lang muir Isotherms of Tetra-alkylphosphonium-Based Ionic Liquids
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Ionic Liquid Films at the Water-Air Interface: Lang muir Isotherms of Tetra-alkylphosphonium-Based Ionic Liquids

机译：水-空气界面处的离子液体膜：基于四烷基phosph的离子液体的朗缪尔等温线

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摘要

The behavior of ionic liquids trihexyl(tetradecyl)phosphonium bis(trifluoromethylsulfonyl)imide and trihexyl(tetradecyl)phosphonium dicyanamide, [P-66614][Ntf(2)] and [P-66614][N(CN)(2)], respectively, at the water-air interface was investigated using the Langmuir trough technique. The obtained surface pressure versus mean molecular area (MMA) isotherms, pi-A, and surface potential versus MMA isotherms, Delta V-A, show distinct interfacial behavior between the two systems. The results were interpreted at a molecular level using molecular dynamics simulations: the different compression regimes along the P-66614][Ntf(2)] isotherm correspond to the self-organization of the ions at the water surface into compact and planar monolayers that coalesce at an MMA value of ca. 1.85 nm(2)/ion pair to form an expanded liquidlike layer. Upon further compression, the monolayer collapses at around 1.2 nm(2)/ion pair to yield a progressively thicker and less organized layer. These transitions are much more subdued in the P-66614][Ntf(2)] system because of the more hydrophilic nature of the dicyanamide anion. The numerical density profiles obtained from the MD simulation trajectories are also able to emphasize the very unusual packing of the four long alkyl side chains of the cation above and below the ionic layer that forms at the water surface. Such a distribution is also different for the two studied systems during the different compression regimes.
机译：离子液体三己基（十四烷基）phosph双（三氟甲基磺酰基）酰亚胺和三己基（十四烷基）phosph双氰胺，[P-66614] [Ntf（2）]和[P-66614] [N（CN）（2）]的行为，使用朗缪尔槽技术分别研究了水-空气界面。所获得的表面压力与平均分子面积（MMA）等温线pi-A，以及表面电势与MMA等温线Delta V-A，显示了两种系统之间的明显界面行为。使用分子动力学模拟在分子水平上解释了结果：沿着P-66614] [Ntf（2）]等温线的不同压缩方式对应于离子在水表面的自组织为紧密凝聚的平面单层在大约MMA值1.85 nm（2）/离子对形成膨胀的液状层。在进一步压缩后，单层在约1.2 nm（2）/离子对处塌陷，以产生逐渐变厚且组织较少的层。这些过渡在P-66614] [Ntf（2）]系统中更为柔和，因为双氰胺阴离子的亲水性更高。从MD模拟轨迹获得的数值密度分布图还能够强调在水表面形成的离子层之上和之下的阳离子的四个长烷基侧链的非常不寻常的堆积。对于两个研究的系统，在不同的压缩方式下，这种分布也不同。

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