LAUSR

Abstract The dynamic interfacial dilational properties of catanionic surfactant mixtures and the relationship with foam stability in the presence of oil are studied in the present work. The dynamic interfacial dilational properties of catanionic mixtures at aqueous-oil interface have been studied by means of oscillating the drop profile method. The mixing ratio of anionic/cationic surfactants and the hydrophobic chain length of the surfactants influence the foam stability in the presence of oil through the interfacial dilational properties. Over a wide range of mixing ratio of SDS/C12TAB, interfacial tension and dilational modulus of the catanionic mixtures reaches similar equilibrium values. But as the mixing ratio approaches 1:1, comparable anionic and cationic surfactants are adsorbed at interface. This significantly speeds up the dynamic adsorption progress, which benefits the fast foaming progress. In addition, the increase of the alkyl chain length of CnTAB in SDS-CnTAB (n = 8, 10, 12, 14, 16) mixtures enhances the equilibrium modulus, but slows down the dynamic adsorption progress. Thus the foamability and stability decreases when surfactants have overlong hydrophobic chains. Overall, the fast generation of a tightly packed interfacial layer is in favor of the foamability and foam stability in the presence of oil.