Experimental Observation of Charged Drop Coalescence Under Electric Field

Electrocoalescence is a method that uses an electric field to separate an aqueous phase from an oil phase. The electric field moves aqueous drops into contact and helps the coalescence of the aqueous phase. However, an excessively high electric field may result in partial or non-coalescence, reducing the efficiency of the process. In this work, we did an experiment to observe the coalescence of a charged drop under an applied electric field. The drop is charged and injected from a needle tip to merge with water at a planar interface, which is located below the tip. The results demonstrate that the aqueous drop can coalesce with the water plane with the electric field below 4.2 kV/cm. With increasing the electric field from a low value, the acceleration of the drop is enhanced, and the coalescence with the water plane becomes faster. When the electric field is increased to 4.2 kV/cm, the non-coalescence between the charged drop and the water plane occurs. Further increase in the field leads to the disintegration of the drop before the coalescence.