Abstract: The interaction between ionic liquid surfactant, 1-dodecyl-3-methylimidazolium bromine(C12mimBr) and anionic dye, methyl orange(MO) was studied using conductometric and surface tension methods in aqueous solutions. The equilibrium constants of the interaction between C12mimBr and MO were derived from the molar conductivities of C12mimBr, MO and mixtures of C12mimBr and MO. At the temperatures of 288.1, 298.1 and 308.1 K, the equilibrium constants are 4.89×105, 4.88×104 and 5.76×103 L/mol, respectively. Thus, the binding process is an enthalpy driving and spontaneous exothermic reaction. Furthermore, the critical micelle concentrations(cmc) of the solutions of C12mimBr and the mixtures of C12mimBr and MO were measured to be 9.1×10-3 and 7.3×10-5 mol/L, respectively. Thus the surface activity of C12mimBr in aqueous solution can be greatly enhanced by MO.

Key words: ionic liquid, methyl orange, interaction, CMC