Aggregation of ionic liquids [C(n)mim]Br (n = 4, 6, 8, 10, 12) in D2O: a NMR study.
Aggregation of ionic liquids [C(n)mim]Br (n = 4, 6, 8, 10, 12) in D2O: a NMR study.
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DOI：
10.1021/jp076467e
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发表时间：
2008-01
期刊：
影响因子：
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通讯作者：
Yang Zhao;Shan Gao;Jianji Wang;Junming Tang
中科院分区：
文献类型：
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作者：
Yang Zhao;Shan Gao;Jianji Wang;Junming Tang
用核磁共振方法研究了溴化1-n-烷基-3-甲基咪唑系列离子液体[C（n）mim]Br（n = 4，6，8，10，12）在298.2K下的水溶液中离子浓度的变化。除[C4 mim]Br在D_2O中的临界聚集浓度和聚集数外，其它离子液体的临界聚集浓度和聚集数均由~ 1H NMR测定。考察了阳离子链长对离子液体聚集行为的影响。利用D_2O溶剂的~ 1H NMR数据研究了离子液体在D_2O中的水合作用，发现离子水合作用与离子液体的阳-阴离子缔合或聚集相互抵消。通过测定自旋-晶格弛豫速率（1/T1），探讨了离子液体中不同质子或阳离子在聚集体中的微环境。有人建议，在聚集体中的咪唑环暴露于水，聚集体的分子运动比离子液体的单体的更受限制。此外，二维1H-1H NOESY测量结果表明，[C（n）mim]Br/D2 O（n = 6，8，10）体系具有阶梯状的微观聚集结构.
Aqueous solutions of five ionic liquids (ILs) of the 1-n-alkyl-3-methylimidazolium bromide family, [C(n)mim]Br (n = 4, 6, 8, 10, 12), were investigated by NMR measurements at 298.2 K as a function of IL concentrations. Critical aggregation concentrations and aggregation numbers of these ILs were determined by 1H NMR except for [C4mim]Br in D2O. The effects of the alkyl chain length of the cations were examined on the aggregation behavior of the ILs. 1H NMR data of the solvent D2O were used to investigate the hydration of the ILs in D2O, and it was found that the ionic hydration and the cation-anion association or aggregation of the ILs offset each other. The microenvironment of different protons of cations of the ILs in the aggregates was probed by determining the spin-lattice relaxation rate (1/T1). It is suggested that the imidazolium rings in the aggregates are exposed to water and that the molecular motion of the aggregates is more restricted than that of the monomers of the ILs. Furthermore, a stair-like microscopic aggregation structure is suggested for the [C(n)mim]Br/D2O (n = 6, 8, 10) systems from 2-D 1H-1H NOESY measurements.