Nanoparticle-laden droplet-liquid film electrocoalescence behaviors: A molecular dynamics simulation

Abstract

Electrocoalescence is an efficient and environmentally friendly process for separating water-in-oil (W/O) emulsions. In this paper, molecular dynamics (MD) simulation method was used to study the electrocoalescence behaviors of nanoparticle-laden (NP-laden) droplet-liquid film. The results showed that the coalescence behaviors successively exhibited three modes, i.e., complete coalescence (CC) mode, critical state, and partial coalescence (PC) mode, with increasing direct current (DC) electric field strengths. The alternating current (AC) electric fields tended to promote the CC mode, and the coalescence efficiencies increased with increasing frequencies. Compared with the pure water droplet, the NP-laden droplets had greater tendencies to exhibit PC mode. In addition, the droplet with large We numbers produced strong impact force, and thus promoted rapid coalescence process. In the two-droplets system, due to the large number of water (H2O) molecules, droplet polarization phenomena were much significant under electric fields, hence resulting in PC mode at small field strengths. It is noteworthy that, at the absence of electric fields, the huge initial kinetic energy (EK) carried by the two droplets could overcome the surface energy (ES) at small We, and thus the droplet was detached from the liquid film. This work can provide theoretical guidance for designing compact and efficient oil–water separators.