Aggregation behavior of ionic liquids in aqueous solutions: Effect of alkyl chain length, cations, and anions
Aggregation behavior of ionic liquids in aqueous solutions: Effect of alkyl chain length, cations, and anions
复制标题
DOI：
10.1021/jp0726889
复制
发表时间：
2007-07-12
影响因子：
3.3
通讯作者：
Kumar, Arvind
中科院分区：
文献类型：
--
作者：
Singh, Tejwant;Kumar, Arvind
用H-1核磁共振（NMR）和稳态荧光光谱研究了离子液体1-丁基-3-甲基咪唑氯[C(4)mim][Cl]、3-甲基-1-辛基咪唑氯[C(8)mim][Cl]、1-丁基-3-甲基咪唑四氟硼酸盐[C(4)mim][BF4]、n -丁基-3-甲基吡啶氯[C(4)mpy][Cl]在水溶液中的自聚集。将质量作用理论应用于H-1核磁共振化学位移的浓度依赖性，确定了聚合性质。聚合性质与先前报道的小角中子散射、电导率和表面张力测量结果相当吻合。通过对水和各种质子的化学位移的详细分析，研究了聚合物的聚集结构。荧光光谱提供了临界聚集浓度（cac）和聚集体微环境的重要信息。从折射率测量的浓度依赖性来看，我们还可以观察到一个与H-1核磁共振和荧光光谱在cac处的断点非常一致。利用折射率/浓度曲线推导出的各种离子表面活性剂的标准自由聚集能δ G(m)度与经典离子表面活性剂相当。
Self aggregation of the ionic liquids, 1-butyl-3-methylimidazolium chloride [C(4)mim][Cl], 3-methyl-1-octylimidazolium chloride [C(8)mim][Cl], 1-butyl-3-methylimidazolium tetrafluoroborate [C(4)mim][BF4], N-butyl-3-methylpyridinium chloride [C(4)mpy][Cl], in aqueous solution has been investigated through H-1 nuclear magnetic resonance (NMR) and steady-state fluorescence spectroscopy. Aggregation properties were determined by application of mass action theory to the concentration dependence of H-1 NMR chemical shifts. Aggregation properties showed fairly good agreement with the previously reported results obtained from small angle neutron scattering, conductivity, and surface tension measurements. A detailed analysis of chemical shifts of water and various protons in ILs has been employed to probe the aggregate structure. Fluorescence spectroscopy provided important information about the critical aggregation concentration (cac) and the microenvironment of the aggregates. We could also observe a break point quite consistent with that of H-1 NMR and fluorescence spectroscopy at cac from the concentration dependence of refractive index measurements. Standard free energies of aggregation Delta G(m)degrees of various ILs derived using the refractive index/concentration profiles were found comparable to those of classical ionic surfactants.