Lakhasly

we measured the refractive index of nine IL-water mixtures over the entire concentration range from pure water to pure IL. These systems showed slightly convex concentration dependence which differs from the ideal mixing law.Furthermore, plots of the IL concentration dependence of the normalized ( = 0 and = 1) completely overlapped for all ILs studied.Importantly, even though the studied ILs have different combinations of cations and anions the results showed almost the same concentration dependence.Thus, the important point is that knowing the refractive index of pure water and pure IL, the refractive index of an IL-water mixture can be estimated easily for an arbitrary IL concentration using Eq. (3).

we measured the refractive index of nine IL-water mixtures over the entire concentration range from pure water to pure IL. These systems showed slightly convex concentration dependence which differs from the ideal mixing law. The experimentally determined maximum deviation of the refractive index from that for an ideal solution exhibited a good linear correlation with the refractive index of the pure IL. In addition, the IL concentration was about 25 mol%, regardless of the IL species. Importantly, even though the studied ILs have different combinations of cations and anions the results showed almost the same concentration dependence. Furthermore, plots of the IL concentration dependence of the normalized ( = 0 and = 1) completely overlapped for all ILs studied. These results suggest that, in terms of refractive index, the specific characteristics of many IL-water mixtures do not appear by normalization④, even though IL-water mixtures have unique structural properties such as a nano heterogeneous structure or water pockets. Thus, the important point is that knowing the refractive index of pure water and pure IL, the refractive index of an IL-water mixture can be estimated easily for an arbitrary IL concentration using Eq. (3). We believe that the information obtained in the present study is useful for future applications in, e.g., industrial processes, though more advanced investigations are required to give a thorough discussion