Liquid dielectric films in a nonuniform electric field: dynamics, perforation, and influence of electrode wettability

A nonstationary electrohydrodynamic model of dielectric film dynamics on a solid substrate in surrounding gas is developed. The mesoscopic multiphase lattice Boltzmann model is applied for simulation of fluid dynamics. The nonuniform electric field is generated by inserting nonconductive parts into the lower electrode. Under the action of a nonuniform electric field, the film can be perforated producing new contact lines. In the case of a round insulating inset, the perforation process is governed by the electric field strength, the film thickness, the radius of nonconductive insets, and the contact angle between the liquid and the solid substrate. Hence the modified expression for the electric Bond number can be introduced, which takes into account both the film thickness and the radius of nonconductive insets. When the inset radius is substantially larger than the thickness of a film, the wetting of the electrode does not play an essential role in the initial perforation but influences the dynamics of the dry spot growth. When the size of the insulating parts is comparable with the film thickness, the situation becomes different. With certain electric field strength, the film is teared faster on a nonwettable surface of inserts but can be preserved on a wettable one. It was shown that the degree of wetting of insulating insets makes the main difference.