Surface properties and microemulsion of anionic/nonionic mixtures based on sulfonate Gemini surfactant in the presence of NaCl

Abstract

The mixing properties of anionic/nonionic surfactant mixtures in the presence of inorganic salts are essential to the industrial application. The equilibrium and dynamic surface tension of the sulfonate Gemini surfactant (SGS12) and alkyl glycoside (APG0810) mixtures were examined using the plate method and drop-shape analysis. Moreover, the Winsor phase diagram and solubility properties of the microemulsion were studied using the salinity scan. Results show that the critical micelle concentration (cmc) of the SGS12/APG0810 mixtures was intermediate between those of the two single surfactants in the presence of NaCl. For the SGS12/APG0810 mixtures, the absolute value of interaction parameters increased as the APG0810 content increased at cNaCl = 0.01 or 0.1 mol/L. The formation of the mixed micelles was spontaneous. At cNaCl = 0.01 mol/L, the initial adsorption (t → 0) of surfactant molecules from the bulk phase to the surface was diffusion-controlled. The salinity scan experiments showed that the optimal solubilization parameters of the SGS12/APG0810 microemulsion decrease with the decrease of the molar fraction of SGS12. However, the concentration range of inorganic salt between the formation and disappearance of Winsor III broadened with the decline in SGS12 content. The impact of temperature on the volume fraction of the middle-phase microemulsion (MPM) was ignorable, indicating the high stability of MPM at the temperature range of 30.0 °C ~ 80.0 °C. At 30.0 ± 0.1 °C, the hydrodynamic diameter of the SGS12/APG0810 MPM was about 28.0 nm, and the number of microemulsion droplets decreased with the increase of APG0810 content. When the total mass fraction of surfactant and cosurfactant was 15%, wNaCl = 5% (brine), Km = 1:3 and Vo/Vw = 1, the interfacial tension between crude oil and the SGS12/APG0810 MPM reached the order of 10−3mN/m. At nSGS12:nAPG0810 = 7:3, the lowest interfacial tension was 9 × 10−4 mN/m. For the SGS12/APG0810 (7:3) mixture, the addition of n-butanol induced the formation of MPM. The concentration range of n-butanol between the formation and the disappearance of Winsor III first increased and then decreased with the increase of surfactant concentration.