Surface and Micellar Properties of Ionic Liquid 1-Dodecyl-3-methylimidazolium Bromide in Aqueous Solution in the Absence and Presence of a Series of Organic Electrolytes

Abstract

The surface and micellar properties (including critical micelle concentration (cmc), surface tension at the cmc (γcmc), adsorption efficiency (pC20), effectiveness of surface tension reduction (∏cmc), the maximum surface excess concentration (Γmax), and minimum surface area per molecule (Amin) at the air–liquid interface) of 1-dodecyl-3-methylimidazolium bromide ([C12mim][Br]) ionic liquid in aqueous solutions were studied in the absence and presence of a series of organic electrolytes by surface tensiometry at 298.15 K and 308.15 K. The electrolytes studied include tetraalkylammonium halides, namely, (CH3)4NBr, (C2H5)4NBr, (C3H7)4NBr, (C4H9)4NBr, (CH3)4NCl, and (CH3)4NI. The results show that the surface tensions as well as the cmc values decrease in the presence of the added electrolytes. Therefore, the electrolytes 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 small effect on the salting-out strength. The ability of the anions and cations to promote the aggregation of [C12mim][Br] decreases in the order of I– > Br– > Cl–, and (C4H9)4N+ > (C3H7)4N+ > (C2H5)4N+ > (CH3)4N+, respectively.