Relevance of brine-oil interfaces in understanding interfacial behavior of asphaltenes

Langmuir pressure-area (π-A) isotherms have been used to investigate the behavior of asphaltene interfacial films, specially at simple water-air interfaces. However, to understand their behavior in complex interfaces, such as those find in crude oil emulsions, more realistic interfaces are essential. Here, asphaltenes were characterized via SEM microscopy, EDS, CHN elemental analysis, and FTIR, and the behavior of their films was investigated at water-air, water-oil, and brine-oil interfaces using π-A isotherms and rheological measurements. Results reveal that the nature of the interface and asphaltene concentration dictate film rigidity and molecular organization. At the water-air, increasing the initial-spread concentration of asphaltenes leads to aggregation, reducing the molecular area and enhancing film rigidity up to a critical threshold of approximately 0.30 m²/mg, beyond which multilayer formation occurs without further increasing rigidity. The presence of oil top-phase induces asphaltene hydrocarbon side-chains to organize towards the oil, resulting in less compact, more flexible films. Conversely, salts in the aqueous phase increases interfacial rigidity due to electrostatic interactions that anchor asphaltene molecules, revealing a compensatory effect between oil-induced hydrocarbon chains organization and salt-induced anchoring. These findings underscore the limitations of using simplified water-air interfaces and highlight that brine-oil interfaces provide a more realistic model for studying asphaltene behavior. Also, novel insights into the molecular-level interactions governing asphaltene film are provided, which helps understanding the interfacial phenomena in complex hydrocarbon-water systems where both salinity and interface type are critical variables.