Heavy Oil−Water Interfacial Properties and Emulsion Stability: Influence of Dilution

We have performed a study of dynamic interfacial tension and rheology of interfaces between water and either crude oil diluted in toluene or in a model oil consisting of toluene, in which pentane-extracted asphaltenes were redissolved. We show that the break point of the curve interfacial tension versus asphaltene concentration is not related to an eventual critical aggregation concentration but rather to the collapse of the asphaltene surface layer. As for other amphiphilic species that adsorb irreversibly at an oil−water interface, the corresponding emulsion stability increases with the amphiphile concentration, even above the collapse point. The behavior of diluted crude oil and model oil are quite similar. However, the surface layers evolve over longer time scales in the case of diluted crude oil, probably because of the contribution of resins that form less polar aggregates with asphaltenes. This results in less stable emulsions, especially before the collapse point.