Coalescence preference in surfactant-laden bubbles of equal size

Abstract

Coalescence preference is the tendency of a bubble merged from two parent bubbles to be placed closer to one of the parents. Coalescence preference has been extensively studied for parent bubbles of different size, but mechanism of coalescence preference in bubbles of equal size have not yet been fully characterized. Here, we use high-fidelity simulations to investigate potential coalescence preference in contaminated bubbles of equal size. Results show that when a clean bubble merges with a surfactant-contaminated bubble of the same size, the merged bubble tends to be closer to the contaminated parent. By analyzing the coalescence events at different surfactant concentrations we also identify a novel preference mechanism characterized by spontaneous self-propulsion of the merged bubble. Elucidating mechanisms of coalescence in surfactant-contaminated bubbles has implications for technological processes involving bubble dispersions in the food and chemical industries where the presence of surfactants is ubiquitous.