Synthesis and Self-Assembly Properties of New Surface-Active 1-Alkylimidazolium Ionic Liquids in Aqueous Media

Abstract

New cationic surface-active ionic liquids (SAIL)were synthesized using 1-alkylimidazolium cations [CnHim](n = 8, 10, 12, 14, and 16) with trifluoroacetate ([CF3CO2])and methanesulfonate ([CH3SO3]) anions as counterions.Their self-aggregation behavior in water was investigatedusing electrical conductivity and fluorescence measurements.Based on the obtained results, the critical micellar concentration(CMC), the degree of counterion dissociation, α, theGibbs free energy of micelle formation, ΔG0mic, and themean aggregation number (Nagg) were determined. Theanalysis of these parameters indicates that these new SAILexhibit certain improved properties with respect to traditionalcationic surfactants. Furthermore, SAIL with[CF3CO2] counterions exhibit lower CMC values thanalkyltrimethylammonium bromide (CnTAB)-type surfactantsand their dialkylimidazolium counterparts with thesame alkyl chain length. It was demonstrated that, in thestudied SAIL, the hydrophobic probe pyrene resides deeperinside the palisade layer of the micelle and the estimatedET(30) polarity values of micellar pseudophase confirm thisresult. The abovementioned outcomes demonstrate that the1-alkylimidazolium cation is suitable to promote aggregationwhen it is accompanied by the appropriate counterions.Consequently, this contribution becomes a valuable firststep toward the potential application of these compounds asa new class of ?designed cationic surfactants.?