Microscopic mechanism for nanoparticle-laden droplet–droplet electrocoalescence: A molecular dynamics study

[Display omitted] •Droplet-droplet electrocoalescence is studied by molecular dynamic method.•The nanoparticle (NP) concentrations affect both the approach and coalescence process.•The electrostatic repulsion between NPs dominate the total interactions at large NP sizes.•Applying high-frequency AC electric fields is time-saving and high-efficiency. Electrocoalescence is an energy-efficient and environmentally friendly process for separating water-in-oil emulsions. In this study, nanoparticle-laden droplet–droplet electrocoalescence behaviors under external electric fields were numerically investigated using molecular dynamics (MD) methods. Good agreement was obtained between numerical results and experimental validation work. The influences of electric field strength, droplet diameter, nanoparticle (NP) concentration, NP size, and electric frequency were systematically examined, analyzed, and discussed from the perspective of intermolecular interactions. The NPs migrated to the liquid bridge to form nanoparticle shell under electric fields, and the NP brown motion increased the breakup probabilities, leading to partial electrocoalescence, which is undesirable in oil–water separation process. As to unequal droplets (droplet pairs of 6&4 nm, 6&6 nm, and 6&8 nm), the daughter droplets were always ejected from the apex of the small droplet. The NP concentrations influence not only the film coalescence process but also the droplet approach process, and high concentrations (0.15, 0.22 and 0.29 mol L−1) resulted in partial coalescence. The NP size also played significant roles during electrocoalescence. At large NP sizes (0.86 & 1.16 nm), the electrostatic repulsion between NPs played the dominant roles in the overall system, accounting for the PC mode with increasing NP size. In addition, applying high frequency (10 & 40 GHz) AC electric fields was found to be a time-saving and high-efficiency method. The results of this work will be potentially useful for optimizing the design of compact and efficient oil–water separators.