Dilational Viscoelastic Properties of Water–FuelInterfaces in Single and Binary Surfactant Systems

The interfacial rheology of a surfactant film surrounding a water-in-oil emulsion influences the stability of the emulsion significantly. In this research, we chose monoolein of molecular weight of 356.54 and pentaerythritol oleate (PETO-B) of molecular weight of 1193.93 as the surfactants and dissolved them in clay-treated ultralow sulfur diesel fuel separately and together to mimic single and binary surfactant systems. The water/fuel interfacial viscoelastic properties were then studied using the oscillation pendant drop method subject to different surfactant concentrations and oscillation frequencies. Surfactant coverage on the interface and the surfactant molecule migration rate were calculated to investigate the viscoelastic phenomenon of the surfactant film. The migration rate of surfactant in the bulk was found to be crucial for the surfactant to effectively compensate the interfacial tension (IFT) gradient caused by interfacial area expansion and compression. Faster moving monoolein molecules coul...