Thermodynamic and micellization behavior of long chain 1-octyl-2,3-dimethylimidazolium bromide [odmim][Br] in aqueous solution in the absence and in presence of a series of alkali salts

Abstract

The alkali salts (0.1 mol·kg−1 LiCl, LiBr, NaCl, NaBr, and KCl) markedly affect the aggregate formation of trisubstituted imidazolium based ionic liquid (IL), 1-octyl-2,3-dimethylimidazolium bromide [odmim][Br] in aqueous media. Various techniques such as surface tension at 298.15 K and conductivity from 288.15 to 308.15 K has been studied. The surface parameters such as critical aggregation concentration (CAC), adsorption efficiency, interface surface pressure, surface tension at CAC, minimum surface cover by a single molecule, maximum area excess concentration were calculated from surface tension measurements with and without salts. The CAC value of trisubstituted IL has been found lower than the CAC value of disubstituted ionic liquid (IL), 1-octyl-3-methylimidazolium bromide [omim][Br]. It suggests that the H-bonding in [omim][Br] is dominant that results in formation of larger aggregates in comparison to smaller aggregates formed by [odmim][Br]. The presence of alkali salts helped in the formation of still larger aggregates of [odmim][Br] because of electrostatic attractive interactions present between the cationic and anionic counter parts. Formation of aggregates at lower concentration predicts that [odmim][Br] acts as a better cationic surfactant.