Aggregation behavior of long-chain imidazolium ionic liquids in ethylammonium nitrate

The aggregation behavior of long-chain imidazolium ionic liquids, 1-alkyl-3-methyl-imidazolium bromide (C(n)mimBr, n=12, 14, 16) was studied by surface tension measurements in a room temperature ionic liquid, ethylammonium nitrate (EAN), at various temperatures. A series of parameters including critical micelle concentration (cmc), surface tension at the cmc (gamma cmc), and the effectiveness of surface tension reduction (Pi(cmc)) were obtained. In addition, from the cmc values and their temperature dependence, we estimated the thermodynamic parameters of the micelle formation, Delta G(m)(0), Delta H-m(0), and Delta S-m(0). The contribution of enthalpy term to the micelle formation is superior to that of entropy term. H-1 NMR was performed to study the CnmimBr micelle formation mechanism in EAN.