In order to investigate the drop-interface coalescence mechanism under pulsatile electric fields

micro-experiments were conducted on the effect of electrical parameters (electric field intensities

frequencies and waveforms) and physical parameters (surface tension

conductivity

primary droplet size and SiO2 particles) with deionized water as dispersed phase and sunflower oil as continuous phase. The results show that two mechanisms exist

i.e. complete coalescence and partial coalescence

during drop-interface coalescence. The dominant factor is the competition of pumping and necking process. Partial coalescence is enhanced with increasing field strengths

while it is decreased with increasing frequencies. This is resulted from the strength of electrostatic force and the stability of droplets under pulsatile fields. With increasing surfactant concentrations

secondary droplets increase rapidly. When the concentration is higher than that of the critical micelle

secondary droplets decrease slightly. With increasing conductivities and SiO2 concentrations

partial coalescence is enhanced first and then decreases. On the other hand

with increasing primary droplet sizes

partial coalescence increases continuously. Among the waveforms utilized in the experiments

constant DC wave has the highest partial coalescence while sawtooth wave has the lowest. The outcome of this work is potentially useful for optimizing the design of compact and efficient oil-water separators.