In this study, the critical micelle concentration (CMC) and surface tension at CMC for ILs A and B and DSILs at various molar ratios (AB0.1-AB0.9) were determined. The obtained data is depicted in Fig. , and the exact values are provided in Table .11 (Supplementary Data). to the Clint's equation (Fig. ; the deviation is visualized as a blue area). The most notable discrepancy was observed for the DSIL AB0.4, where the experimental CMC value was as much as 45% lower compared to the theoretical one. Similar deviations from the "ideal" binary mixture behaviour were also observed previously for mixtures of anionic/cationic and ionic/non-ionic surfactants. These non-additive effects in surfactant mixtures predominantly stem from the entropy of the diffuse counter-ion layer outside the micelle interfacial boundaries, as well as the length of the tails and the charges in the cation and anion. The occurrence of the above-described synergistic effect in DSILs makes it a legitimate strategy to combine two active surfactants in well-defined ratios to reduce the amount of surfactants introduced into the environment. Synthetic auxins show higher efficiency when applied in the form of aqueous solutions with the addition of a surface-active adjuvant, therefore, such DSILs with a surface-active cation and pesticidal anions can guarantee excellent efficacy without necessity of use any other additives. Furthermore, the analysis of the surface tension of the aqueous solution for the DSILs AB0.1-AB0.9 and ILs A and B at their respective CMCs indicated a linear dependence on the xdic value, as illustrated in Fig. . No significant deviation from the linear relationship (R > 0.98) indicates lack on any unexpected interactions in the analyzed systems with water and air.