Combined interfacial shear rheology and microstructure visualization of asphaltenes at air-water and oil-water interfaces

Asphaltenes are surface-active polyaromatic molecules in crude oil that are known to deposit in pipelines or stabilize water droplets by flocculating at interfaces resulting highly viscous emulsions, leading to significant flow assurance problems. Commercial dispersants have been developed to disturb asphaltene aggregation to mitigate deposition, but their role on the interfacial properties of asphaltene films is unclear. In this study, we elucidate asphaltene interfacial rheology at air-water and oil-water interfaces at high and low asphaltene surface coverage and in the presence of dispersants. A modified Langmuir trough with double-wall ring rheometer is used to simultaneously visualize the microstructure of asphaltene interface and measure the rheological responses. Two surface coverages, 0.5 and 4 μg cm^-2, show widely different rheological responses at air-water interfaces. Strong yielding behavior was observed for higher coverage while a less yielding behavior and wider linear viscoelastic regime were observed for the lower coverage. Additionally, asphaltenes at decane-water interfaces were less shear-thinning than at air-water interfaces. Surface pressure-area compression-expansion curves show that the interface is more compressible in the presence of commercial chemical dispersants. This combined imaging and interfacial rheology platform provide an effective method to correlate asphaltene microstructure to interfacial rheological properties.