Abstract: The dilational viscoelasticity properties of decane-water interface containing two demulsifiers with straight chain SP169 (octadecanol polyoxypropylene-polyoxyethylene ether) and branch chain AE121 (tetraethylenehexamine polyoxypropylene-polyoxyethylene ether)respectively were investigated. The dependence of dilational modulus on dilational frequency and demulsifier concentration was expounded. The influences of two demulsifiers on dilational properties of oil-water interface containing surface-active fraction from crude oil were also studied. The dynamic interfacial tensions between solutions of two demulsifiers and decane were measured and were related to the interfacial dilational rheology properties. The results showed that the two demulsifiers could decrease remarkably the dilational modulus of oil-water interface containing surface-active fraction from crude oil. At low concentration, because of stronger adsorption ability, the effect of decreasing dilational modulus of SP169 was better. But above a certain concentration, AE121 was preferential because of its higher substitution ability. Since the interface film containing demulsifier had a certain dilational modulus itself, the dosage of demulsifier could not be much higher.

Key words: Demulsifier, Dilational modulus, Dilational elasticity, Interfacial tension