Ageing and burst of surface bubbles

Abstract

Upon burst, surface bubbles transfer biological and chemical material from water bodies to the air we breathe via the production of droplets. An understanding of what shapes the size and payload of such droplets starts by understanding the fundamental physics of bubble birth, drainage and burst. Our combined experimental and theoretical investigation focuses on film-drop-producing surface bubbles. Controlling fluid properties such as temperature, salinity and volatility, coupled with changes of ambient air saturation, we elucidate the ageing and lifetime of bubbles. We derive and validate a generalized bubble cap drainage model accounting for both curvature-pressure-induced drainage and Marangoni flows induced by the coupling between the bubble and its surrounding air. We show that this deterministic drainage is coupled with stochastic local perturbations, both intrinsic and extrinsic, from impacts by mist droplets to microbubbles. We derive the conditions for such perturbations to be lethal to the cap film, involving the competition of mixing and drainage time scales on the bubble, the film thickness, the size of the perturbation and the local Marangoni stresses introduced. We explain how the mixing dynamics on the cap ensures that bursts mostly occur at the foot of bubbles rather than on their cap. Our study sheds light on the coupling between the deterministic cap thinning and the stochastic events leading to bubble death. We conclude that ubiquitous water contaminants enable the birth of a bubble, sustain it through its ageing, but ultimately also kill it.