Isopiestic measurements have been carried out on the aqueous solutions of both NaH2Cit and NaH2Cit + [C8mim][Br] over a range of temperatures at atmospheric pressure. Vapor-liquid equilibrium data such as water activity, vapor pressure, osmotic coefficient, activity coefficient and Gibbs free energies were obtained through the isopiestic method. The effect of temperature on the constant water activity lines of aqueous [C8mim][Br] + NaH2Cit systems has been studied. An interesting aspect of such ILs is that the [Cnmim]+ cations possess inherent amphiphilic character when their alkyl group is a longer hydrocarbon chain. The results show that [C8mim]Br behaves as a surfactant in water and forms aggregates in water with the critical micelle concentration (cmc) about 0.18 mol.kg-1. Micellization of this ionic liquid in water has also been discused in this work.
