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'-CO2H-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'-CO2H-Im]Br exhibits considerably lower critical micelle concentration (cmc) and surface tension at cmc (gamma(cmc)), higher adsorption efficiency (pC(20)) and effectiveness of surface tension reduction (pi(cmc),), indicating the incorporation of carboxyl group favors micelle formation. The average aggregation number (N-agg) values of [N-C, N'-CO2H-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'-CO2H-Im]Br was also studied. It is found that there exists a minimum cmc at nearly 38 degrees C, which is higher than that of [C(12)mim]Br. (C) 2012 Elsevier B.V. All rights reserved.