Functionalized Silica Nanoparticles within Multicomponent Oil/Brine Interfaces: A Study in Molecular Dynamics

Stability control of nanoparticles within polar and nonpolar liquid interfaces can be influenced by surface effects and molecular-level interactions. This study uses fully atomistic molecular dynamics to investigate the behavior of functionalized silica nanoparticles (NPs) at crude oil/brine interfaces as a function of salt, brine concentration, temperature, and NP surface functionalization. The light crude oil model used in this study comprises aromatics, alkanes and cycloalkanes. Silanized (H-passivated), PEGlyated, and sulfonated functionalized NPs are used to account for hydrophilicity variations. The size effect of the functional groups is evaluated for PEGlyated NPs. The highest contact angles (NP moves toward the oil phase) are observed for monovalent (NaCl) solutions, at higher salt concentrations, and for PEGlyated NPs. The findings indicate that the Young-Laplace equation is still valid at nanoscale for spherically symmetric nanoparticles. The mobility of all NPs indicates that the self-diffusion coefficient is ten times faster along than across the interface. The results also show that aromatic molecules adsorb to the NP surface, even on the face located in the brine phase, where they form patchy domains on each nanoparticle evaluated. As this result can greatly affect the stability of NPs at oil/brine interfaces, it has implications for several technological applications.