Asphaltene-stabilized emulsions: an interfacial rheology study

In the current study, we consider the rheological properties of an asphaltene-stabilized water-oil planar interface. Using rheological techniques we are able to measure time-dependent changes of the interfacial film mechanical properties. To elucidate the critical role of interfacial rheology we have directly compared rheology measurements to single droplet-droplet coalescence times measured using our in-house built Integrated Thin Film Drainage Apparatus (ITFDA). In all interfacial aging experiments, step-change behaviour in the droplet coalescence time is measured with the coalescence time increasing from a few seconds to no coalescence. Correlating the rheology and droplet coalescence data we identify that the condition for no coalescence corresponds to a shear rheological property G’ > G”. We extend the study to consider the disruption of asphaltene-stabilized films following the introduction of an emulsion breaker, ethyl-cellulose (EC). At low demulsifier concentration (0.2 ppm), the asphaltene-stabilized emulsion is very stable with less than 20% water drop out. The prolonged stability corresponds well to the interconnected network of asphaltenes as visualized by Brewster Angle Microscopy and the strongly elastic film. In contrast, at a slightly higher demulsifier concentration (1 ppm), the emulsion is considerably less stable (~50% water drop out), forming an island-like film of asphaltenes which exhibits viscous dominant properties and no measurable elastic contribution, G’ = 0 mN/m