Zhao Man, Wu Boning, Castner Edward W
Department of Chemistry and Chemical Biology, Rutgers, The State University of New Jersey, Piscataway, New Jersey 08854, USA.
J Chem Phys. 2020 Dec 7;153(21):214501. doi: 10.1063/5.0031989.
Ionic liquids (ILs) with long alkyl substituents are amphiphilic, which leads to a bicontinuous liquid structure. The strongly interacting anionic and cationic head groups form a long range charge network, with the hydrocarbon tails forming a nonpolar domain. Such nonpolar domains have been shown to dissolve a variety of neutral organic solvents. In mixtures of ILs with solvents the neutral organic molecules residing in the nonpolar domains experience different environments and friction from the charged cations and anions. Thus, the neutral molecules diffuse much faster than predicted by hydrodynamic scaling using the average viscosity of the mixture. In this work, we report studies on the structure and transport properties of mixtures of 1-octanol with the IL trihexyltetradecylphosphonium bis(trifluoromethylsulfonyl)imide (P /NTf ). The majority of the atom fraction in the P cation comprises four hydrocarbon substituents. The unique amphiphilic nature of ILs with the P cation makes 1-octanol fully miscible with the IL at ambient temperatures. X-ray scattering experiments show that the IL structure persists in the mixtures for 1-octanol mole fractions as large as x = 0.90. The self-diffusion coefficients of the three molecular species in the mixtures were measured by NMR experiments. The self-diffusion of the P cation is well described by the Stokes-Einstein equation, while the diffusivity of the NTf anion is slightly lower than the hydrodynamic prediction. The measured diffusivities of octanol in these mixtures are 1.3-4 times higher than the hydrodynamic predictions.
具有长烷基取代基的离子液体（ILs）具有两亲性，这导致形成双连续液体结构。强相互作用的阴离子和阳离子头基形成长程电荷网络，而烃链尾部形成非极性域。已证明这种非极性域可溶解多种中性有机溶剂。在离子液体与溶剂的混合物中，存在于非极性域中的中性有机分子会经历与带电阳离子和阴离子不同的环境和摩擦力。因此，中性分子的扩散速度比使用混合物平均粘度通过流体动力学标度预测的速度快得多。在这项工作中，我们报告了关于1-辛醇与离子液体三己基十四烷基鏻双（三氟甲基磺酰）亚胺（P/NTf）混合物的结构和传输性质的研究。P阳离子中的大部分原子分数包含四个烃取代基。具有P阳离子的离子液体独特的两亲性使得1-辛醇在环境温度下与离子液体完全互溶。X射线散射实验表明，对于高达x = 0.90的1-辛醇摩尔分数，离子液体结构在混合物中仍然存在。通过核磁共振实验测量了混合物中三种分子物种的自扩散系数。P阳离子的自扩散可以用斯托克斯-爱因斯坦方程很好地描述，而NTf阴离子的扩散率略低于流体动力学预测值。在这些混合物中测得的辛醇扩散率比流体动力学预测值高1.3 - 4倍。
