Effect of electric field strength on deformation and breakup behaviors of droplet in oil phase: A molecular dynamics study

Electrostatic demulsification process is frequently accompanied by the occurrence of droplet breakup, which will cause a fall in the efficiency of droplet electro-coalescence. To uncover mechanisms of droplet deformation and breakup in the water-in-oil (W/O) emulsion, molecular dynamics simulations were used here to investigate the influence of electric field strength on the motion behavior of a single droplet. The results showed that with increasing field strengths, the droplet underwent deformation, breakup at one end, breakup at both ends, and breakup in the middle part, respectively, which is consistent with the experimental findings at mesoscopic scales. Quantum chemical calculations and noncovalent interaction analysis found that non-bonded potential energies between water molecules played a dominant role in droplet morphology transformation, supporting the reasonableness for gas-phase molecules instead of oil-phase molecules. Besides deformation ratio (Dr), solvent accessible surface area (SASA) is also an important parameter for characterizing the degree of droplet deformation at the molecular level. Electrostatic attraction among water molecules and external electric field force were found to be the key factors affecting droplet deformation. At field strength of 1.4 V nm−1, the majority of the hydrogen bonds between H2O had a very brief lifetime, 0.79 ps. Hydrated ions and ion migration perform critical roles during droplet breakup. This study fills an important gap in the molecular dynamics study of electrostatic coalescence by introducing real oil molecules.