Study of salt effects on the aggregation behavior of ionic liquid 1-dodecyl-3-methylimidazolium bromide in aqueous solution

Abstract

The effect of organic electrolytes Me4NBr, Et4NBr, Pr4NBr, Bu4NBr, Me4NCl and Me4NI on the aggregation behavior and thermodynamic properties of surface active ionic liquid (SAIL) 1-dodecyl-3-methylimidazolium bromide ([C12mim]Br) in aqueous solution was studied by volumetric, compressibility and conductometric measurements at different temperatures. The results show that all the electrolytes investigated effectively reduce critical micelle concentration and therefore have a salting-out effect on the aggregation of [C12mim]Br in aqueous solutions. It was also found that the salting-out-inducing anions are predominately responsible for the observed effect, while the cations have a very smaller effect on the salting-out strength. The ability of the anions to promote the aggregation of SAIL decreases in the order of I−>Br−>Cl−; however all the investigated cations Me4N+, Et4N+, Pr4N+ and Bu4N+ have a similar salting-out strength. Changes in the apparent molar volumes and isentropic compressibilities upon micellization were derived and the infinite dilution apparent molar properties of the monomer form of [C12mim]Br were determined. Furthermore the effect of electrolyte on the degree of anionic binding and the thermodynamic parameters of aggregation for [C12mim]Br in aqueous solutions were determined.