Microemulsion and interfacial properties of anionic/nonionic surfactant mixtures based on sulfonate surfactants: The influence of alcohol

• Microemulsions with n -butanol and n -pentanol as cosurfactants have strong solubilization ability. • Decreased interfacial tension does not necessarily enhance the solubilization capacity of microemulsion. • Dilatational modulus of the oil-water interface film increases with the increased carbon chain of the regular alcohol. • The microemulsion with n -butanol as cosurfactant behaved excellent properties of bi-phasic wetting and oil film removal. The influence of alcohols on the microemulsion and interfacial properties of sulfonate and nonionic surfactant mixtures (LAS-IPA/AEO9 mixture) were explored. Surface properties and interaction parameters were investigated to determine the optimum molar ratio of the LAS-IPA to AEO9, and the subsequent experimental studies in this paper were based on the system of mixtures ( n LAS-IPA : n AEO9 (4:6)). The microemulsion phase behaviors of LAS-IPA / AEO9 / alcohol / n -decane / water were investigated by constructing a pseudo-ternary phase diagram. Results suggest that the microemulsion systems with n -butanol and n -pentanol as cosurfactants behave have optimal solubilization capacity when the corresponding alcohol to mixed surfactant (K m value) mass ratios are 1:1 and 1:1∼1:2, respectively. The solubilization capacity of the two systems reached their maximum in the temperature range of 35 °C–40 °C. The hydrodynamic diameters of microemulsion were determined by employing dynamic light scattering (DLS), and the average hydrodynamic diameters of microemulsion increased with the carbon number of alcohol, which ranges from 12 nm to 21 nm. Moreover, the equilibrium oil-water interfacial tension, the dynamic adsorption mechanism, and the dilational viscoelasticity of the oil-water interfacial film were studied using spinning-drop method and drop shape analysis, respectively. The results shows that equilibrium oil-water interfacial tension decreased with increased carbon number of the regular alcohol in the system. However, the decrease of interfacial tension with decreased K m is not significant when the carbon numbers of regular alcohol are 5 and 6. At the initial stage, diffusion-controlled adsorption processes were followed with n -propanol and n-butanol as cosurfactants when the K m values were 1:2, but systems of the other two cosurfactants yielded mixed kinetics-diffusion control. The dilatational modulus of oil-water interfacial film increased with the carbon number increase in regular alcohol or the decreased K m value. The contact angles of n -butanol based microemulsion system at the hydrophilic interface and the lipophilic interface reached 20° and 18°, which had excellent bi-phasic wettability property. At the same time, the oil film removal efficiency of the n -butanol based microemulsion was the highest, which was close to 100% at 24h.