Molecular dynamics simulations of nanoparticle-laden drop–interface electrocoalescence behaviors under direct and alternating current electric fields

Abstract

Electrocoalescence is an energy-efficient and environmentally friendly process for separating water-in-oil emulsions. In this study, nanoparticle-laden drop–interface electrocoalescence behaviors under direct current (DC) and alternating current (AC) electric fields were numerically investigated using molecular dynamics methods. Good qualitative agreement was obtained between numerical results and experimental validation work. In this report, the influences of the electric field strength, nanoparticle concentration, and electric field frequency on the electrocoalescence process are systematically examined, analyzed, and discussed from the perspective of intermolecular interactions. The coupling of the hydration effect of ions and the strong interactions between silicon dioxide (SiO2) nanoparticles and water molecules was found to give rise to partial drop–interface electrocoalescence. The critical cone angle at which a transition from complete to partial electrocoalescence occurs was found to be 34.41°. A larger water intermolecular distance and a greater tendency for partial coalescence was observed in the nanoparticle-laden (NP-laden) droplets than in a pure water drop. Compared to a DC electric field, an AC electric field tended to cause complete drop–interface electrocoalescence, and the efficiency of complete coalescence was found to increase with increasing frequencies ranging from 10 to 200 GHz (GHz). The results of this work will be potentially useful for optimizing the design of compact and efficient oil–water separators.