Temperature dependence of micellization behavior of N,N′-didodecyl-N,N,N′,N′-tetramethylhexane-1,6-diammonim dibromide and 1-dodecyl-3-methylimidazolium bromide in aqueous solutions

Abstract Micellar behaviors of mixed surfactants N,N′-didodecyl-N,N,N′,N′-tetramethylhexane-1,6-diammonium dibromide (12-6-12)/1-dodecyl-3-methylimidazolium bromide (C12mimBr) in aqueous media have been investigated by electrical conductivity measurement and isothermal titration microcalorimetry (ITC) over the temperature range 298.15–313.15 K. The critical micelle concentration (cmc) and degree of ionization (β) were determined, and the thermodynamic properties of micellization ΔGmico, ΔHmico and ΔSmico were evaluated according to the pseudophase separation model. A one-parameter Margules equation was used to correlate the cmc values to calculate the mole fractions and the activity coefficients of two surfactant components, which were used to obtain the excess properties GE, HE and SE. It was found that addition of small amount of 12-6-12 significantly enhanced the formation of 12-6-12/C12mimBr mixed micelles. Thermodynamic properties of the 12-6-12/C12mimBr mixed micelles and their dependences on the temperature and the composition were analyzed to reveal the interactions in the mixed 12-6-12/C12mimBr aqueous solutions and their close relations to the dissociation of counterion.