Determining diffusion coefficients of ionic liquids by means of field cycling nuclear magnetic resonance relaxometry
Determining diffusion coefficients of ionic liquids by means of field cycling nuclear magnetic resonance relaxometry
复制标题
DOI：
10.1063/1.4882064
复制
发表时间：
2014-06-28
影响因子：
4.4
通讯作者：
Roessler, E. A.
中科院分区：
文献类型：
--
作者：
Kruk, D.;Meier, R.;Roessler, E. A.
报告了三种离子液体的场循环核磁共振 (FC NMR) 弛豫研究：硫氰酸 1-乙基-3-甲基咪唑鎓 (EMIM-SCN, 220-258 K)、四氟硼酸 1-丁基-3-甲基咪唑鎓 (BMIM-BF4, 243-318 K) 和六氟磷酸盐 1-丁基-3-甲基咪唑鎓（BMIM-PF6，258-323 K）。在10 kHz-20 MHz频率范围内测量了H-1自旋晶格弛豫率R-1(omega)的色散，并通过相应频率范围内BMIM-PF6上的F-19自旋晶格弛豫测量来补充该研究。根据 H-1 弛豫结果，确定 EMIM-SCN、BMIM-BF4 和 BMIM-PF6 中阳离子的自扩散系数。这是通过执行分析来完成的，该分析考虑了所有相关的分子内和分子间弛豫对 H-1 自旋晶格弛豫的贡献，并受益于菲克扩散的通用低频色散定律特征，该特征在低频下产生 R-1 对频率平方根的线性依赖性。根据 F-19 弛豫，确定 BMIM-PF6 的阴离子和阳离子扩散系数。从 FC NMR 弛豫测量获得的扩散系数与脉冲场梯度 NMR 报告的结果非常一致。这表明核磁共振弛豫测量可以被视为确定离子液体中阳离子和阴离子扩散系数的替代途径。 (C) 2014 AIP 出版有限责任公司。
Field Cycling Nuclear Magnetic Resonance (FC NMR) relaxation studies are reported for three ionic liquids: 1-ethyl-3-methylimidazolium thiocyanate (EMIM-SCN, 220-258 K), 1-butyl-3methylimidazolium tetrafluoroborate (BMIM-BF4, 243-318 K), and 1-butyl-3-methylimidazolium hexafluorophosphate (BMIM-PF6, 258-323 K). The dispersion of H-1 spin-lattice relaxation rate R-1(omega) is measured in the frequency range of 10 kHz-20 MHz, and the studies are complemented by F-19 spin-lattice relaxation measurements on BMIM-PF6 in the corresponding frequency range. From the H-1 relaxation results self-diffusion coefficients for the cation in EMIM-SCN, BMIM-BF4, and BMIM-PF6 are determined. This is done by performing an analysis considering all relevant intra-and intermolecular relaxation contributions to the H-1 spin-lattice relaxation as well as by benefiting from the universal low-frequency dispersion law characteristic of Fickian diffusion which yields, at low frequencies, a linear dependence of R-1 on square root of frequency. From the F-19 relaxation both anion and cation diffusion coefficients are determined for BMIM-PF6. The diffusion coefficients obtained from FC NMR relaxometry are in good agreement with results reported from pulsed-field-gradient NMR. This shows that NMR relaxometry can be considered as an alternative route of determining diffusion coefficients of both cations and anions in ionic liquids. (C) 2014 AIP Publishing LLC.