The adsorption behavior of amphiphilic long-chain imidazoliumionic liquids (ILs), n-alkyl-3-methylimidazolium halides, [Cnmim][X], n=12, 14, 16 and X=Cl−, Br−, I−, at the interface of n-butyl acetate+water system was studied. The ILs bulk concentration range of 1.00·10−5–1.00·10−2 mol·dm−3 and temperature of 293.2–318.2 K were applied. The interfacial tension of the system significantly decline due to the excellent action of ILs like surfactants. Under the same conditions, the interfacial activity appears reasonably in the order of [C16mim][I] N [C16mim][Br] N [C16mim][Cl] ≫[C14mim][Br] N [C14mim][Cl] ≫[C12mim][Cl], consistent with alkyl chain length and the kind of halide anions. Molecules of the used ILs exhibit ideal adsorption within the used concentrations and the data were satisfactorily reproduced by the Szyszkowski adsorption model. Consistently, effectiveness of adsorption increases with the anion polarization and the number of carbon atoms in alkyl chain; however, temperature leads this parameter to decrease. On the other hand, adsorption tendency increases with either of anion polarization, alkyl chain length and temperature. Meanwhile, negative standard free energies were consistent and showed spontaneous adsorptions.
