LAUSR

Abstract The dilational rheological properties of aqueous solutions of anionic surfactant petroleum sulfonate (KPS), zwitterionic surfactant alkyl sulfobetaine (ASB) and their mixtures have been investigated at the kerosene-water interface by the oscillating drop method. The influences of time, dilational frequency, bulk concentration and interfacial pressure on the dilational properties have been expounded. The experimental results show that the nature of film containing anionic surfactant KPS molecules is determined by the diffusion-exchange process between the bulk and the interface. On the other hand, the in-film process, such as the orientation change of hydrophilic groups, controls the properties of adsorption layers formed by betaine ASB molecules. The dilational rheological behaviors of KPS-ASB mixtures are close to those of ASB. In addition, the complex system gets the largest dilational modulus at higher bulk concentration, due to a synergistic effect between KPS and ASB caused by electrostatic attraction. The mixed adsorption of KPS and ASB may lead to more compact films and result in higher interfacial dilational modulus at optimum ratio of adsorbed KPS to ASB molecules. The mixed adsorption of KPS and ASB molecules may lead to more compact film and result in larger interfacial dilational elasticity at higher concentration. Graphical Abstract