Aggregation Behavior of Long-Chain N -Aryl Imidazolium Bromide in a Room Temperature Ionic Liquid

The aggregation behavior of long-chain N -aryl imidazolium ionic liquids (ILs), 1-(2,4,6-trimethylphenyl)-3-alkylimidazolium bromide [C n pim]Br ( n = 10, 12, 14), was investigated in a room temperature IL, 1-butyl-3-methylimidazolium tetrafluoroborate ([bmim][BF 4 ]) by surface tension measurements. Freeze-fracture transmission electron microscopy (FF-TEM) and dynamic light scattering (DLS) measurements further verified that micelles are formed. A relatively lower critical micelle concentration (CMC) and smaller micelle size were observed compared with that of N -alkylimidazolium ILs [C n mim]Br. The main reason for this phenomenon is that the electrostatic repulsion between the head groups of [C n pim]Br is weakened due to the incorporation of the 2,4,6-trimethylphenyl group. The thermodynamic parameters of micelle formation of [C n pim]Br in [bmim][BF 4 ] were estimated from the CMC values and their temperature dependence. The micelle formation process is enthalpy-driven in the investigated temperature range, similar to the case in water. The novel N -aryl imidazolium ILs present strong fluorescence properties in [bmim][BF 4 ], indicating their potential application in the field of photochemistry.