Dilatational response of an asphaltene-model molecule stabilizing the oil-water interface near the onset point of precipitation

Defined by their solubility class, asphaltenes represent the most polar, aromatic, and the heaviest fraction of crude oil. They are known to strongly adsorb at oil-water interfaces forming viscoelastic films that confer solid-like mechanical properties that stabilize water-in-oil emulsions. It is suggested that asphaltenes form the most stable water-in-oil emulsions close to the onset point of precipitation, in which soluble and insoluble asphaltene nanoaggregates are present in solution. It is speculated that at this point asphaltenes have the greatest heteroatom content and are highly surface active. The formation of these emulsions leads to undesired flow assurance problems for the oil and gas industry that require demulsification to prevent operational challenges and costs. Given the heterogeneity in chemical composition, structure, and molecular weight of natural asphaltenes, it remains challenging to identify how their aggregation, precipitation, and diffusion behavior at oil-water interfaces promote stability. To address this challenge, we use small-angle X-ray scattering (SAXS) to investigate the structure and aggregation behavior of asphaltenes and asphaltene-model molecule violanthrone-79 (VO-79). In addition, we compare the dilatational rheology response of soluble asphaltenes at the oil-water interface using oscillating pendant drop measurements. The direct connection between structure and the dilatational response of oil-water interfaces stabilized by soluble asphaltenes is important for understanding their interfacial behavior and their role in driving the emulsification process. This work contributes to providing insights for designing energy-efficient demulsification strategies.