The temperature was controlled using a Fisherbrand FBH604 thermostatic bath (Fisher, Germany, accuracy ±0.1 °C). The determination of the contact angle (CA) was based on the sessile drop method. The drops of solution are deposited on a solid hydrophobic surface (paraffin). The images of the drops were taken with a CCD camera, digitized and evaluated using Young-Laplace fitting. The CA was determined as the slope of the tangent line at the contact point between the 3 phases (solution, paraffin surface, and air). The measured error of the CA determination in this method is estimated to be less than 0.1° by the manufacturer. previously developed method . However, on the basis of the FT-IR spectra acquired in situ during synthesis, it was established that the quaternization product formed in satisfactory amounts as early as 5 h after the start of the process, which was 1 hour less than the time reported in previous studies . The resulting bromide was isolated by filtration followed by washing with an apolar solvent, and hexane was substituted with a significantly safer heptane . These changes made it possible to reduce the negative environmental impact of the process. The formation of water during synthesis, combined with the highly hygroscopic properties of ion exchange products, resulted in high water contents in the raw products (approximately 4-6 %, Table ) and difficulties in removing the water. Such high water contents would significantly affect the physicochemical properties of the obtained DSILs (e.g., viscosity, density, and refractive index) and their analysis . Therefore, an effort was made to remove most of the water from the DSILs via a two-step azeotropic distillation process (see a result of the above method, it was possible to significantly reduce the amounts of water in the obtained DSILs by 2.5 times (AB0.2) to 6.5 times (AB0.9). The exact water contents after drying the systems are summarized in Table and ranged from 0.6 % (AB0.9) to 1.7 % (AB0.2). This was likely due to an increase in the strength of the DSIL-water hydrogen bonding as the molar proportion of the MCPA anion increased. The drying process revealed that the remaining water must therefore have been relatively tightly bound to the ionic system. Further dehydration of such highly hygroscopic DSILs would require sophisticated methods, and further analyses would have to take place in a dry inert gas atmosphere to achieve substantially reduced water contents (<2000 ppm), as demonstrated in other studies. However, it should be borne in mind that the obtained ILs are intended for use in aqueous solutions; thus, the increased water content in the raw products does not constitute a significant issue for their industrial application.