Abstract: The dilational viscoelasticity behavior on oil-water interfaces formed by surface active constituents with different average molecular weights and atom ratios of H to C, which were distilled by supercritical fluid extraction and fractionation(SFEF) method from Iranian heavy oil, were investigated. The interfacial relaxation processes were investigated by interfacial tension relaxation method. The dependencies of dilational elasticities and viscosities on dilational frequency were expounded. It is shown that when the dilational frequency was lower, dilational elasticities of the constituents was about zero; dilational elasticities increased when the dilational frequency became bigger at a medial frequency; and when the dilational frequency was higher, the dilational elasticities was close to its limiting value. It is also shown that the dilational viscosities showed a maximum value with the change of frequency. The dilational elasticities increased along with the increase of number average molecular weights and decrease of atom ratios of Hto Cin the samples. With the increase of average molecular weights and decrease of atom ratios of Hto Cin the samples, slow relaxation processes gradually appeared and the contribution of them increased, the characteristic time of similar processes of different samples also increased. The results illustrate that the constituents containing large condensed ring aromatic compounds that have large conjugated structure played a more important role in film-forming and film rigidity than the constituents of small molecule.

Key words: Active constituents in crude oil, Dilational modulus, Dilational elasticity, Dilational viscosity, Interfacial tension relaxation, Interfacial dilational viscoelasticity