Surfactant behavior of ionic liquids (ILs) has recently attracted much attention. Here, adsorption of amphiphilic long chain imidazolium ionic liquids, 1-hexadecyl-3-methylimidazolium halide ([C16mim][X] with X = Cl, Br and I) on the interfacial tension of n-butyl acetate + water system, as recommended system for investigations, was studied. The used ILs act as excellent surfactants and significantly reduce the interfacial tension of this system. The corresponding interface activity is rationally appeared in the order of [C16mim][I] > [C16mim][Br] > [C16mim][Cl]. An almost linear interfacial tension decrease by temperature was also relevant in all cases. The Szyszkowski adsorption equation was revealed as a satisfactory model to fit the experimental data; therefore, IL molecules behaved ideal with no interaction at the interface. In this regard, the Langmuir maximum interface excess, minimum area occupied by adsorbed molecule, equilibrium adsorption constant and standard free energy of adsorption were obtained at different temperatures for each IL.
