Refractive index was determined by using an Automatic Refractometer J357 (Rudolph Research Analytical, Hackettstown, NJ) with electronic temperature control at 20 °C for all ILs and DSILs. In addition, refractive indices at higher temperatures (30-80 °C) for the singleanion ILs, as well as for the DSIL with molar ratios of MCPA and dicamba anions of 5:5. The apparatus was calibrated using deionized water before use, and the accuracy of refractive index measurements was ± 2•10 -4 according to the manufacturer's specifications. Based on the experimental refractive index values obtained at 20 °C for parent ILs A and B, differences between the experimental values recorded for DSILs and the theoretical nD 20 values was calculated according to the equation below: