Indexed on: 25 Jan '17Published on: 25 Jan '17Published in: Langmuir
Asphaltenes are a solubility class of crude oils comprising polyaromatic and heterocyclic molecules with different interfacial activities. Previously neglected effects of compositional mixture on dilatational rheology are discussed in the light of diffusional relaxation models. It is demonstrated that reported deviations from the Lucassen-van den Tempel (LVDT) model for a single component solution could largely originate from a distribution in adsorption coefficients within the asphaltenes class. This particularly applies to the peculiar gel point rheology previously ascribed to asphaltenes cross-linking at the interface. Furthermore, an extensive bibliographical review shows that asphaltenes dilatational rheology data always verify the main features of diffusional relaxation, including a decrease in modulus at high bulk concentration and phase shift values always lower than 45 degrees. Using diffusional relaxation concepts, the reanalysis of the most extensive dataset so far confirms recently published work showing that asphaltenes exhibit a unique equation of state irrespective of adsorption conditions. This equation of state proves very similar for bitumen and petroleum asphaltenes. Finally, a numerical application of a binary diffusional model proves efficient to capture with the same parameters both dynamic interfacial tension and dilatational rheology. It appears that a minority of asphaltenes (less than 10%) have a much stronger interfacial activity than the bulk of them as previously demonstrated by fractionation. These results open up for a re-interpretation of the physical mechanisms of asphaltenes adsorption in terms of classical amphiphilic behavior, with a potential impact on emulsion breaking and Enhanced Oil recovery strategies.