Bursting bubbles and water-to-air-transfer : interplay between underlying physics and microbial contamination

Abstract

Surface bubbles are very efficient at transporting microorganisms and chemicals from water bodies to the atmosphere: upon burst, they release a multitude of droplets known to shape climate and to participate to airborne disease transmission. In this thesis, we combined controlled laboratory experiments with theoretical modelling to study the environmental and in-situ factors that control the droplet population emitted by large surface bubbles. First, we showed that a global Marangoni flow on bubbles cap due to temperature differences, evaporation, and presence of chemicals such as in saltwater can significantly alters the thinning and lifetime of bubbles. This Marangoni dynamics shapes the drainage and thickness evolution of bubbles, until they eventually rupture by nucleation of a hole in their cap. Second, we then proposed a physical picture that explains how and why micrometer-thick bubbles puncture naturally: we showed how local perturbations due to minute contaminants or intrusions can lead to hole nucleation. These findings explain the evolution of the cap thickness and the lifetime of bubbles in relatively clean water. We then studied the influence of microorganism contamination. We discovered that bacterial secretions can make bubbles live longer and indirectly enhance their thinning. As a consequence, bubbles in contaminated water emit smaller, faster, and more numerous droplets than in clean water: microorganisms can alter the physics of bubble ageing and burst to enhance their own water-to-air transfer.