From Individual to Collective Behaviour of Imidazolium Ionic Liquids - Water Mixtures.

M. MIRENDA; KARIN GUTKOWSKI; BEATRIZ C. BARJA

Congreso; EUCHEM 2012 ? MOLTEN SALTS AND IONIC LIQUIDS; 2012

The existence of local heterogeneous environments in pure, room-temperature ionic liquids is extensively reported in the literature through different experimental and simulations experiments. Generally, experiments rely on the study of pure or high-concentration solutions to obtain information about the system. In this work, we study the behavior of 1-butyl-3-methylimidazolium Chloride (bmimCl) in water solutions for a wide range of concentrations (2 > C bmimCl > 10-5) by different techniques: UV-Vis spectroscopy, steady-state emission, ATR-FTIR and conductimetry). Some of these results are shown in Figures 1 and 2. FIG. 2: Conductivity vs Log C, the change in the slope can be seen at C~0.02M. Inset graph: Log Intensity vs Log C, a change in the slope can be seen at C~0.02M.     FIG. 1: ATR-FTIR spectrum of pure bmimCl in water at different concentrations (in molality).                                                 We find that at concentrations C < 0.01M the system behaves as expected for dilute solutions: the conductivity is linear with the concentration, an absorption peak at 210 nm, characteristic of imidazolium ring, is observed, and no fluorescence is detected. For C > 0.01M, the slope of the conductivity changes. Also, we observe a broad absorption band appearing in the region of 220 to 400 nm together with a characteristic red-edge effect in the emission spectra (not shown in the figures). In the case of the IR measurements (an example shown in Figure 1), the profiles of the IR bands in D2O, associated with the vibrational modes of the butyl chain (2800 ? 3000 cm-1 ), change when the concentration changes. In our work, we discuss the existence of two different regimes- typical dilute and particular concentrated. In the latter, the collective behaviour of the molecules dominates the behaviour of the system and, as a consequence, the change of the properties of the ImILs.