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 by interfacial tension relaxation method. The dependence of dilational modulus on dilational frequency was expounded. Our results show that when the dilational frequency is lower, the dilational modulus of the two demulsifiers approaches zero; the dilational modulus of the two demulsifiers increases when the dilational frequency becomes higher in the range of medial frequency; and when the dilational frequency is much higher, the dilational modulus of the two demulsifiers reaches to a limiting dilational viscoelasticity. It is also shown that dilational modulus of the two demulsifiers approaches a maximum value near the critical micelle concentration. Along with the increase of demulsifier concentration, the number of relaxation processes gradually increases and the contribution of them also changes regularly.

Key words: Demulsifier, Dilational modulus, Dilational elasticity, Interfacial tension relaxation, Interfacial dilational viscoelasticity