Dilute oil-in-water emulsion initiates multiple holes formation during bubble bursting

Abstract

The air bubble bursting dynamics involve intricate interfacial phenomena of millisecond timescale, which are of interest in many natural and industrial processes. The current study concerns bubble containing oil droplets with size comparable to bubble cap thickness. The assumption is that the dynamics of bubble bursting and aerosol formation will be modified as oil droplets interact with the air-water interface during drainage. Indeed, the experiments show that with the increase of the droplet spreading coefficient (S), the average film retraction speed decreases and the average film thickness increases at breakup. Notably, as S reaches 3.6 mN/m, a distinct multiple hole formation phenomenon has been observed for the first time during bubble bursting. The frequency of multiple hole formation increases with increasing S, and is as high as 22 holes per bursting event observed when S = 21.3 mN/m. The multiple holes evolve with time and form convoluted ligament structures that finally break up into much more aerosolized droplets. However, after normalization, all droplet size distribution is well predicated by a Gamma distribution.The results highlight the importance of the interfacial physiochemistry for the bubble cap rupture, regarding the wetting state between the oil droplets, air, water phase.