NMR Study for Self-aggregation of 1-Butyl-3-methylimidazolium Bromide in Aqueous Solution

Abstract

Self-aggregation of 1-butyl-3-methylimidazolium bromide ([bmim]Br) in D₂O has been investigated using NMR spectroscopy. The ¹H spin-lattice relaxation times (T₁) 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 ¹H-T₁ decreased below 0.1 mol dm^-3. The estimated ¹³C-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 D₂O.