Studies of synergism between sulfonate and nonionic surfactant

In order to study the synergism between sulfonate and nonionic surfactant for lowering interfacial tension at oil/water interface, three branched alkylbenzene sulfonates and three polyoxyethylenated nonionic surfactants were used. The interfacial tensions of individual surfactants and their mixtures against a series of alkane homologues were measured. And the effects of hydrophilic - lipophilic ability of surfactant, mixing ratio, and salinity of aqueous phase on synergism were discussed. Experiment results showed that the hydrophilic-lipophilic ability of surfactant mixture contained alkylbenzene sulfonate and nonionic surfactant was additive. When the hydrophilic nonionic surfactant was added to the lipophilic sulfonate 8C18ΦS, the hydrophilic-lipophilic ability of surfactant mixture was moderate, the interfacial tension reduced and synergism was achieved. However, when the hydrophilic nonionic surfactant was added to the hydrophilic sulfonate(3G10ΦS or 7C14ΦS), the surfactant mixture was still hydrophilic and the interfacial activity was low. Moreover, the mixing ratio of volume and the dosage of NaCl could effectively influence the synergistic effect between sulfonate and nonionic surfactant. The lowest interfacial tension of 8G18ΦS/LAP-9 was of 4. 0 × 10^-4mN/m with 2:1 mixing ratio and 1% NaCl, and that of 3C10ΦS/LAP-9 and 7C14ΦS/LAP-9 was between 0.4-1.0 mN/m and 0.035-0.13mN/m respectively.