Max Planck Institute for Polymer Research , Ackermannweg 10, 55128 Mainz, Germany.
Institute of Physics, Johannes Gutenberg University Mainz , 55128 Mainz, Germany.
J Phys Chem B. 2017 Jan 26;121(3):620-629. doi: 10.1021/acs.jpcb.6b11220. Epub 2017 Jan 12.
A common feature of ionic liquids composed of cations with long aliphatic side chains is structural heterogeneities on the nanometer length scale. This so-called microphase separation arises from the clustering of aliphatic moieties. The temperature dependence of the liquid bulk structure was studied by small-angle X-ray and neutron scattering for a set of methylimidazolium ([CCim], [CCim]) based ionic liquids with tris(pentafluoroethyl)trifluorophosphate ([FAP]), bis(trifluoromethylsulfonyl)imide ([NTf]), and bis(nonafluorobutylsulfonyl)imide ([NNf]) anions. The experimental data is quantitatively analyzed using a generalized Teubner-Strey model. Discussion of the resulting periodicity d and correlation length ξ shows that the structural heterogeneities are governed by the interplay between the alkyl chain length, the geometry of the anion, and entropic effects. Connections between the mesoscopic correlation functions, density, and entropy of fusion are discussed in comparison to alcohols. The observed dependencies allow predictions on the mesoscopic correlation functions based on macroscopic bulk quantities.
具有长脂肪侧链阳离子的离子液体的一个共同特征是纳米尺度上的结构不均匀性。这种所谓的微相分离源于脂肪部分的聚类。通过小角度 X 射线和中子散射研究了一系列基于甲基咪唑鎓([CCim]，[CCim])的离子液体的液体体结构的温度依赖性，这些离子液体具有三（五氟乙基）三氟磷酸盐([FAP])、双（三氟甲基磺酰基）亚胺([NTf])和双（全氟丁基磺酰基）亚胺([NNf])阴离子。使用广义 Teubner-Strey 模型对实验数据进行了定量分析。对所得周期性 d 和相关长度 ξ 的讨论表明，结构不均匀性受烷基链长度、阴离子几何形状和熵效应的相互作用控制。与醇相比，讨论了介观相关函数、密度和熔化熵之间的关系。观察到的依赖性允许基于宏观整体量对介观相关函数进行预测。
