Density of DSILs was determined using an Automatic Density Meter DDM2911 (Rudolph Research Analytical, Hackettstown, NJ) equipped with a Peltier module for precise temperature control, with the mechanical oscillator method. The measurement was acquired at 20 °C in 5 repetitions for each of the samples (approximately 1.0 cm 3 ). Moreover, densities were determined at higher temperatures (30-80 °C) for the single-anion ILs, as well as for the DSIL with molar ratios of MCPA and dicamba anions of 5:5. Before the series of measurements, the apparatus was subjected to a two-point calibration using deionized water and air as the references. After each series of measurements, the densimeter was washed with water and organic solvents (methanol and acetone) and dried with airflow. The uncertainty of the density measurement was estimated to be less than 5•10 -4 g cm -3 . Based on the experimental density values obtained at 20 °C (ρ20), and average molecular weights of ILs and DSILs (Mw), molar volume (Vm 20 ), average volume of a single ionic pair (Vip 20 ), and excess molar volume (Vm E20 ) were calculated according to the equations below :