Nanomechanical Characteristics of Trapped Oil Droplets with Nanoparticles: A Molecular Dynamics Simulation

Nanoparticles (NPs) possess great potentials in applications to enhanced oil recovery (EOR), the underlying mechanisms of which however remain to be explored. In this study, the motion of NPs and the local pressure distribution in a trapped oil droplet/nanofluid system in confined nanochannels are scrutinized by molecular dynamic simulations. Depending on the particle wettability, three different motion patterns have been observed: hydrophilic NPs are more likely to be adsorbed on the solid surface of the channel and stay close to the three-phase contact areas, hydrophobic NPs tend to move inside the oil droplet as clusters, and NPs with mixed hydrophobicity are prone to be trapped at the oil-water interface. It is shown that the existence of NPs introduces high local pressure in the nanochannels, especially at locations where NPs aggregate. Significantly, in the three-phase contact area for hydrophilic NPs, the local pressure distribution features the postulated structural disjoining pressure reported in the literature. For the first time, our molecular dynamics simulation results elucidate nanoparticle-induced structural disjoining pressure at the atomistic scale. The results thus provide a better understanding on the fundamentals of nanofluids in confined channels and serve as guidelines for the design of NPs for EOR applications.