Electric field-induced deformation and breakup of water droplets in polymer-flooding W/O emulsions: A simulation study

Abstract

Polymers have a significant impact on the electrostatic demulsification efficiency of water-in-oil (W/O) emulsions by altering the motion characteristics of water droplets. To uncover the underlying micro-mechanism behind electric field-induced deformation and breakup of polymer-containing water droplets, we employed the molecular dynamics (MD) method to investigate the effect of different polymer concentrations (cp) on droplet motion under a DC electric field. The simulation results indicated that polyacrylamide (PAM) molecules possess a prominent electrostatic potential (ESP), resulting in a strong electrostatic attraction between PAM and water. The interface film of the droplet was found to exhibits high strength due to the formation of hydrogen bonds with a lifetime of 1 ps between polymers. The addition of polymers increased the polarity of the droplets, thereby promoting their deformation and breakup under an electric field. Both polarized polymers and ions migrated by carrying water molecules, which ultimately led to droplet breakup. At cp = 0.0221 mol·L−1, the critical field strength (Ec) for droplet breakup was the lowest, at only 0.672 V·nm−1. As cp > 0.0221 mol·L−1, the steric hindrance of PAM molecules and the strong interfacial film impeded the breakup of the droplets. These findings provided a theoretical basis for enhancing the electrostatic demulsification efficiency of polymer-flooding crude oil.