Influence of Nonionic Surfactants on the Surface and Interfacial Film Properties of Asphaltenes Investigated by Langmuir Balance and Brewster Angle Microscopy

The interfacial Film properties of asphaltenes and their mixtures with nonionic surfactants (polyoxyethylene nonylphenols) have been investigated using a Langmuir trough and a Brewster angle microscope (BAM). The effects of asphaltene concentration, surfactant/asphaltene ratio, and surfactant HLB (hydrophilic lipophilic balance) have been studied at the air water interface. The BAM image for asphaltenes show irregular domains with various structures even before compression, indicating preaggregation of asphaltenes in the spreading solution. The film morphology depends on both concentration and total amount of asphaltenes in the spreading solution. Lower proportions of surfactant (5 wt %) compared to asphaltenes increases the film compressibility and disperses the asphaltene domains; however, the behavior of the surface film is still dominated by asphaltenes. When the proportion of surfactant is increased to 50 wt %, surfactant molecules can occupy the interface top layer with multilayer formation by asphaltenes beneath this layer, and a relatively homogeneous film is observed by BAM. At the oil water interface, surfactant was examined as both an inhibitor and a demulsifier for water-in-oil emulsions. Surfactants with intermediate HLB = 14.2 are most efficient in both cases preventing asphaltene adsorption at the interface by competitive adsorption and breaking the existing asphaltene film by displacement of asphaltenes from the interface.