Coalescence of hydrolysed polyacrylamide and surfactant based droplet on water–oil interface under an electric field

The petroleum industry uses electrocoalescers to remove brine/water from crude oil. Aqueous droplets show three drop-interface phenomena under an electric field: coalescence, partial coalescence, and non-coalescence. In this work, we studied the effect of hydrolysed polyacrylamide (HPAM) and sodium dodecyl sulfate (SDS) surfactant-containing droplets on water–oil interface coalescence phenomena. Our results reveal that the electrocapillary number plays a crucial role in distinguishing between coalescence and partial coalescence, and it depends on the droplet phase type. We have defined a scaling, which is the ratio of a critical electrocapillary number to the Ohnesorge number (CaE/Oh), to observe a pattern with a radius of primary droplets for different droplet phase systems. The critical value of CaE/Oh for the transition from coalescence to partial coalescence is found as CaE/Oh= 9.5 ±1 for HPAM droplets, CaE/Oh= 6.5 ±0.5 for SDS droplets, and CaE/Oh= 3.8 ± 0.5 for a mixture of 3000 ppm HPAM and SDS droplets. The bridge dynamics during the partial coalescence show the growth and decay of the bridge radius as linear. HPAM with an SDS droplet shows a faster bridge decay than HPAM and an SDS-based droplet alone. However, the electrocapillary number affects how long it takes for this growth-to-decay transition to occur. The outcome of this study helps design the electrocoalescer for separating complex water-in-oil emulsion.