Impact of imidazolium-based ionic liquid, functionalized with aromatic compounds, on thermophysical and aggregation properties

New imidazolium-based ionic liquids ([But(MIM)Br][Br]) functionalized with aromatic compounds (clioquinol, 1-naphthol, 2,4-dibromophenol, and eugenol) were synthesized at excellent yields (81–94 %). Thermal stability was evaluated, and it was found that the ionic liquids (ILs) were stabler than their aromatic precursors — the least stable decomposed at 152 °C and the most stable at 241 °C. The ILs had greater water solubility than their aromatic precursors and a higher density than water. The self-assembly properties of the ILs in an aqueous medium were determined, and the free energy of aggregation values indicated that the aggregation process was exergonic. The order of the critical aggregation concentrations, which are related to the hydrophobicity of the ILs, were as follows: [DBPB(MIM)][Br] < [CliB(MIM)][Br] = [NaphtB(MIM)][Br] < [EgB(MIM)][Br]. The contact angle of the samples with the PET surface, spreading coefficient, and surface free energy were used to evaluate the ILs’ hydrophobicity. In this IL series, [DBPB(MIM)][Br] had the highest hydrophobicity and the greatest tendency to form aggregates in water (lower critical aggregation concentration). By contrast, [EgB(MIM)][Br] had the lowest hydrophobicity and the least tendency to self-organize in solution. Our results highlight the influence that different aromatic compounds have on the physicochemical properties of ILs in polar solvents.