Many water-in-oil emulsions are stabilized by an interfacial film consisting primarily of asphaltenes. It is of interest to determine the interfacial structure or configuration of the asphaltenes on the interface so as to design more effective emulsion treatments. The configuration of asphaltenes on the water-oil interface was evaluated from a combination of molar mass, interfacial tension, drop size distribution, and gravimetric measurements of model emulsions consisting of asphaltenes, toluene, heptane and water. Molar mass measurements were required because asphaltenes self-associate. The level of self-association depends on asphaltene concentration, the asphaltene/resin ratio, solvent type, and temperature. It is critical to determine the asphaltene molar mass at emulsion conditions in order to correctly convert measured masses to a molar basis. Plots of interfacial tension versus the log of asphaltene molar concentration were employed to determine the average interfacial area of asphaltene molecules on the interface. The mass and moles of asphaltenes per area of emulsion interface were determined from the molar mass data as well as drop size distributions and gravimetric measurements of the model emulsions. The results indicate that asphaltenes form monolayers on the interface even at concentrations as high as 40 kg/m~3. The area occupied by the asphaltenes on the interface was constant indicating that the asphaltenes simply extend further into the continuous phase as they self-associate. The thickness of the monolayer ranged from 4 to 10 nm, depending on the asphaltene concentration.
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