Droplet coalescence in coupled shear and electric fields: A molecular dynamics study.

• Study of droplet coalescence under coupled shear and electric fields. • Increasing shear rate enhances droplet coalescence, yet surpassing the critical shear rate (γ = 7.5 × 109 s−1) results in elongation, impeding full coalescence. • Optimal droplet coalescence occurs at a θ = 25° angle, balancing shear force impact and horizontal electric field influence. • Droplet coalescence is primarily driven by shear forces, electrostatic attraction among water molecules, and directed charge migration. Water droplet coalescence in coupled flow and electric fields is a phenomenon extensively observed in petrochemical, microfluidic, and chemical synthesis processes; however, the existing research in this domain lacks the necessary depth. This paper employs a molecular dynamics approach to elucidate the microscopic mechanisms governing droplet aggregation in water-in-oil emulsions. The investigation spans various shear rates and droplet angles, considering droplet morphology and molecular interactions. The study reveals an interrelation between shear rate and droplet angle effects on droplet coalescence, both seeking to understand the impact of the flow field's shear effect on the electrocoalescence of water droplets. Increasing the shear rate proves advantageous to droplet aggregation up to a certain threshold; however, complete coalescence is hindered beyond the critical shear rate, γ = 7.5 × 109 s−1. Augmenting the droplet angle amplifies the shear force exerted by the flow field on the droplets, while diminishing the radial electric field force. Consequently, an optimal droplet angle of θ = 25° facilitates comprehensive droplet merging. The analysis of the coalescence process, interaction energy, charge density and radial distribution function shows that the approximate process of droplet motion is as follows: the shear effect drives the droplets to approach, and then the directional migration of charge and electrostatic attraction between water molecules drive the coalescence. The existence of a moderate shear effect enables complete droplet coalescence. This study offers theoretical guidance for the exploration of dynamic electrocoalescence technology. [ABSTRACT FROM AUTHOR]