Molecular Insights into the Modified Silica Nanoparticle-Induced Emulsification of Crude Oil-in-Water Emulsions: Experimental and Simulation Study

Numerous experimental results have demonstrated that Pickering emulsions stabilized by modified silica nanoparticles exhibit excellent performance in enhanced oil recovery. This study investigates the microcosmic mechanism of emulsion stability formed by three typical silica nanoparticles (hydrophilic SiO2 (HSO), hydrophobic SiO2 (LSO), and Janus SiO2 (JSO)) by using experiments and molecular dynamics simulations. Based on the results of the interfacial tension and emulsification index (EI) measurements, JSO exhibits the greatest interfacial activity, whereas LSO possesses a similar ability to stabilize emulsions as JSO. Then, the number density distribution and solvent-accessible surface area (SASA) are calculated to explore in detail the interfacial distribution of nanoparticles affected by oil components in the aqueous phase. The mechanism of nanoparticle stabilization emulsion is further investigated via the radial distribution function (RDF), interaction energy, and independent gradient mode based on Hirshfeld partition (IGMH), which is verified via steered molecular dynamics (SMD) simulations. It is found that the more intensive hydrophobic effect among nanoparticles in comparison to the weaker interaction between asphaltenes and nanoparticles should be responsible for the special "nanoparticles channel" formed by LSO, which is beneficial to emulsion stability. The interfacial membrane barrier of JSO, caused by van der Waals interactions and weak hydrogen bonds with asphaltenes, significantly improves the stability of the emulsion. This work is of great significance to the in-depth understanding of the mechanism by which modified nanoparticles stabilize emulsions.