Interfacial dilational rheology of fatty acid methyl ester and alkyl benzene sulfonate mixed solutions

The dilational rheological properties of aqueous solutions of anionic surfactant sodium 3,4-diheptylbenzene sulfonate (C7C7phS), nonionic surfactant oxyethylated fatty acid methyl esters (C18=E10) 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 in-film process, such as the orientation change of EO chain, controls the properties of adsorption layers formed by nonionic surfactant C18=E10 molecules. On the other hand, the diffusion-exchange process plays the crucial roles in determining the nature of film containing anionic surfactant C7C7phS molecules. The dilational rheological behaviors of C18=E10/C7C7phS mixtures in the presence of 1 × 10−5 mol·L−1 C7C7phS are close to those of C18=E10. At the same time, mixtures at mole ratio 1:1 show similar behaviors with C7C7phS. The mixed adsorption of C18=E10 and C7C7phS may lead to more compact films and result in higher interfacial elasticity.