Surface and interfacial tension of nonylphenol polyethylene oxides sulfonate

The equilibrium and dynamic surface tension of nonylphenol polyethylene oxides sulfonate (NPEnS, n = 3, 5 and 7) were investigated; and, the effect of electrolytes (NaCl, MgCl2 and CaCl2) on the interfacial tension between NPEnS solution and dodecane was discussed. It was found that the critical micelle concentration (cmc) of NPEnS is almost the same. The surface tension at cmc and minimum area per molecule increase with increasing the EO number. The time required to attain the equilibrium surface tension decreases with increasing surfactant concentration and the EO number. Adsorption process for NPEnS concentration above cmc is a mixed diffusion-kinetic adsorption mechanism. Interfacial tension between NPEnS solution and dodecane increases with the increase of EO number at studied electrolyte concentrations (NaCl concentration from 10 to 210 g/L, CaCl2 and MgCl2 concentration from 0.1 to 10 g/L). Most of IFT measured keeps in the order of 10− 1 mN/m magnitudes in a wide range of electrolytes concentrations, which indicates that NPEnS is insensitive to electrolyte and suitable for co-surfactant in high salinity reservoirs.