The effects of surfactant/hydrocarbon interaction on enhanced surfactant interfacial activity in the water/hydrocarbon system

The phosphorus-based cationic surfactant dodecyltriphenylphosphonium bromide (C12TPB) was systematically evaluated for its interfacial activity by the interfacial tension (IFT) measurement and emulsification experiments. Interestingly, the C12TPB molecules exhibited the differential interfacial activity in the water/hydrocarbon systems, which was mainly dependent on the hydrocarbon structure. The C12TPB could largely reduce the water/toluene LET to 4.11 x 10(-2) mN/m, whereas the water/n-octane IFT was slightly decreased to 42 mN/m at the same C12TPB concentration (10,000 mg/L). Moreover, the C12TPB stabilized emulsion in the water/toluene system showed the preferable stability and the smaller emulsion droplet than that in the water/n-octane system. The control experiments used another three kinds of hydrocarbons (n-hexane, cyclohexane, benzene) and isobutanol demonstrated that the pi-pi stacking interaction between C12TPB and aromatic hydrocarbon molecules greatly enhanced the C12TPB interfacial activity. The interaction energy calculation and the molecular dynamics simulation were employed to further confirm the proposed mechanism. (C) 2019 Elsevier B.V. All rights reserved.