Prediction of Refractive Indices of Binary Mixtures of Ionic Liquids and Water

In the present work, we have successfully predicted the refractive indices of binary mixtures containing ionic liquids (ILs) and water as a component following the approach of Gladstone–Dale and Newton. These approaches were proposed as adequate to predict the refractive indices of mixtures containing imidazolium-based ILs with water or ethanol. It requires just the knowledge of the density and refractive index of pure components to obtain the value of refractive index of binary mixtures at any composition. We have selected 30 binary systems that contain ILs from imidazolium, ammonium, pyrrolidinium, and pyridinium families for validation. The tested data comprise of more than 400 mixture points. The results are presented in terms of average percentage deviations (APDs) from the experimental values. The Gladstone–Dale method gives better results compared to the Newton approach. The reasons why these approaches give large APDs for some mixtures are discussed in the manuscript.