Aggregation of 1-dodecyl-3-methylimidazolium nitrate in water and benzene studied by SANS and 1H NMR

Abstract

Aggregation of imidazolium-based ionic liquid, C₁₂mim⁺NO₃⁻, in both polar solvent of water and nonpolar solvent of benzene was elucidated by electrical conductivity, small-angle neutron scattering (SANS), and ¹H NMR measurements. The electrical conductivities of C₁₂mim⁺NO₃⁻–water solutions at 298 K as a function of ionic liquid concentration showed a break point at 8.4 mmol dm⁻³ as a cmc. However, those of C₁₂mim⁺NO₃⁻–benzene solutions drastically increase in accordance with a cubic function of concentration, but without a break point. The SANS profiles of both aqueous and benzene solutions obviously differ from each other. The profiles of the aqueous solutions indicated the formation of polydisperse spherical micelles. Those of the benzene solutions revealed Ornstein–Zernike behavior. Thus, C₁₂mim⁺NO₃⁻ forms clusters in the benzene solutions, but the shape of clusters is indefinite. On the basis of the ¹H NMR chemical shifts of the aqueous solutions, the effect of nitrate on the formation of micelles was discussed on a microscopic scale. Furthermore, the interactions among C₁₂mim⁺, NO₃⁻, and benzene molecules in the benzene solutions were considered according to the ¹H NMR data.