NMR study for self-aggregation of 1-butyl-3-methylimidazolium bromide in aqueous solution.

Self-aggregation of 1-butyl-3-methylimidazolium bromide ([bmim]Br) in D(2)O has been investigated using NMR spectroscopy. The (1)H spin-lattice relaxation times (T(1)) of the [bmim](+) increased with the decrease of concentration in the range of 0.1-3.0 mol dm(-3) as expected, however, in contrast, the (1)H-T(1) decreased below 0.1 mol dm(-3). The estimated (13)C-activation energies indicated that the rotational mobility of the butyl-chain was more restricted than that of the imidazole ring at 0.1 mol dm(-3), whereas such a significant difference was not observed at 3.0 mol dm(-3). These results suggest that [bmim](+) forms micelle-like aggregations below 0.1 mol dm(-3) in D(2)O.