The structural organization in aqueous solutions of ionic liquids

The ¹H NMR combined with the local composition (LC) model has been employed to investigate the structural organization of two aqueous solutions of ionic liquids (ILs), namely 1‐ethyl‐3‐methylimidazolium tetrafluoroborate (EmimBF₄) and n‐butylammonium nitrate (N4NO₃). The correlation of chemical shifts using the LC model shows that the self‐association of IL plays the leading role, and water prefers to interact with IL rather than self‐association in IL‐rich region. Instead the network of water molecules is established in water‐rich region, because the self‐association of water predominates. Furthermore, the difference between the local and the bulk composition presents the turnover at x_(IL) (mole fraction of IL) close to 0.6 for EmimBF₄/water, which is in accordance with the change of excess function. Accordingly, it could be presumed that the excess properties for N4NO₃/water system should behave turnover at x_(IL) ≈ 0.55 since the local and the bulk exhibit maximal difference at this composition. © 2008 American Institute of Chemical Engineers AIChE J, 2009