Anomalous dynamic behavior of ions and water molecules in dilute aqueous solution of 1-butyl-3-methylimidazolium bromide studied by NMR

Dynamic properties of 1-butyl-3-methylimidazolium bromide ([bmim]Br) in D2O were investigated by NMR. The diffusion coefficients of [bmim]+and HDO were determined separately by the pulse field gradient method. The dynamics of Br− was estimated by the half-widths of the signals of 81Br-NMR. The results indicate that an anomalous dynamics, especially for [bmim]+, is evident in the region below ∼0.1 M (0.0019 in the mole fraction of [bmim]Br). For [bmim]+ and HDO, maxima appeared in the curves of the diffusion coefficients plotted against the concentration. The relaxation time, T2, for Br− showed a break in slope at this composition. Probable interpretations on these findings are presented.