Aggregation behavior of COOH-functionalized imidazolium-based surface active ionic liquids in aqueous solution

A series of novel COOH-functionalized imidazolium-based surface active ionic liquids (SAILs), N-alkyl-N′-carboxymethyl imidazolium bromide ([N-C n , N′-CO 2 H-Im]Br, n   =   10, 12, 14), was synthesized. Their aggregation behavior in aqueous solution was investigated by surface tension and steady-state fluorescence measurements. From surface tension data, a group of micellization parameters was obtained. Compared with 1-alkyl-3-methylimidazolium bromide ([C n mim]Br) bearing the same hydrocarbon chain, [N-C n , N′-CO 2 H-Im]Br exhibits considerably lower critical micelle concentration (cmc) and surface tension at cmc (γ cmc ), higher adsorption efficiency ( pC 20 ) and effectiveness of surface tension reduction ( π cmc ), indicating the incorporation of carboxyl group favors micelle formation. The average aggregation number (N agg ) values of [N-C n , N′-CO 2 H-Im]Br, determined by fluorescence quenching method, are slightly different from those of [C n mim]Br. The effect of temperature on the aggregation behavior of [N-C 12 , N′-CO 2 H-Im]Br was also studied. It is found that there exists a minimum cmc at nearly 38   °C, which is higher than that of [C 12 mim]Br.