Coulomb split evolution behavior in different growth stages of droplets

ABSTRACT The dynamic behavior of droplets under the electric field has attracted extensive research interests due to its widespread industrial applications, such as emulsification, transesterification and drug delivery. In this study, we investigated experimentally the novel Coulomb splitting behavior of charged droplets at different growth stages in the surrounding fluid when exposed to an electric field. Besides, we accurately captured the microscopic features of charged droplets and the evolutionary details of the Coulomb splitting process under different aelectric field strengths. The force analysis of the droplets attached to the nozzle under the electric field was carried out. The new phenomena of expansion-contraction deformation, bifurcation breakup, and annular membrane oscillation behavior of droplets were obtained successfully by manipulating the electric field. It is noted that in the initial growth stage, the droplet deformation and breakup degree are relatively large. Under high electric field strength, the surface area of the formed liquid film is about nine times the surface area before droplet crushing. It is found that the pressure difference formed inside and outside the liquid film could promote the backflow phenomenon of shattered small droplets. Furthermore, three regimes of Coulomb splitting were distinguished with the change of electric bond number B o E in the overall phase diagram.