Coalescence Dynamics of Oil Droplets on an Air-Water Interface Driven by Surface Waves

This study reports the unique phenomenon of the coalescence of oil droplets floating over the water surface. For the first time, the coalescence has been initiated through the creation of externally generated low-amplitude surface waves. We used a simple and cost-effective method to manifest the surface waves over the free surface of water to study the merging dynamics. The time-lapse images depict the entire stage of parent droplets merging. The study reveals that the coalescence time required for the complete transformation of parent droplets into the resultant droplet increases as the number of parent droplets over the free surface of water increases. We studied the time-dependent variation in the velocity of two non-identical parent droplets. The experiment reveals that the smaller droplet propagates faster than the larger droplet over a free surface of water. The peak velocities of the two droplets are 2.0 cm/s and 1.07 cm/s, respectively. The point of deposition of droplets does not influence the coalescence phenomenon; whether the droplets are deposited at the center of the petri dish or the wall, they still show coalescence. However, the droplets that are deposited near the center of the petridish propagate faster compared to those deposited near the wall due to the higher intensity of vibration at the center.