Electrohydrodynamic generation of high-viscosity microdroplets: A lattice Boltzmann study

Generating high-viscosity microdroplets with precise control remains a significant technical challenge. A hybrid color gradient lattice-Boltzmann and finite-difference method is employed to simulate electric-field-induced droplet generation in a T-junction. The method is first validated against cases of droplet generation with and without an electric field. Subsequently, it is employed to examine the effect of the electric capillary number CaE on the droplet volume and detachment position, characterized by the equivalent diameter Deq and the dimensionless distance s*, respectively. These quantities are examined over a wide range of viscosity ratio M and capillary number Ca. As M increases, indicating a more viscous dispersed fluid, Deq initially decreases rapidly and then exhibits a slight increase, whereas s* increases monotonically. At M=10, the droplet generation process becomes prone to instability, with the detachment point gradually moving downstream. With increasing Ca and fixed M=10, Deq decreases monotonically, while s* increases monotonically. Both Deq and s* monotonically decrease with increasing CaE, indicating that the electric field not only reduces the droplet volume but also suppresses the downstream migration of the detachment point. Finally, two phase diagrams are presented to illustrate the dependence of Deq and s* on Ca and CaE for the generation of high-viscosity droplets with M=10. These phase diagrams provide guidance for selecting operating parameters to produce high-viscosity droplets with controllable volume.