Effect of Nanoparticles and Surfactants on the Interfacial Behavior and Viscous Fingering of Immiscible Fluids under Nonequilibrium Conditions

Fingering is crucial when a low-viscosity fluid (e.g., water) displaces a high-viscosity fluid (e.g., oil). While this phenomenon has been investigated for bare oil-water systems, the impact of nanoparticle and surfactant presence at the interface on the fingering behavior, has not been studied in detail. The hypothesis is that the presence of interfacially active molecules in synergy with nanoparticles affects the development of fingering instabilities and that the wettability of the particles is important in the resulting behavior. To test this hypothesis, the effects of different types of nanoparticles in the presence of nonionic surfactants on the oil-water interface and in channel flow were probed via coarse-grained computations. Finger-like instabilities were characterized by the driving force for the flow, the three-phase contact angle, and the deformation of the interface. In the presence of surfactants, the instability developed at lower pressure drops compared with the bare oil-water case. In the presence of both surfactants and nanoparticles, a larger driving force was required for the instabilities to occur compared to either the bare oil-water system or the surfactant-only case. A critical contact angle dictated the detachment of the oil droplet from the channel wall. Our findings and discussion can be used for predicting displacement efficiency and interfacial instabilities that are common in industrial processes involving immiscible flows, such as in enhanced oil recovery, separation processes, and environmental remediation of the subsurface.