Enriching particles on a bubble through drainage: Measuring and modeling the concentration of microbial particles in a bubble film at rupture

Abstract

The concentration of microbes and other particulates is frequently enriched in the droplets produced by bursting bubbles. As a bubble rises to the ocean surface, particulates in the bulk liquid can be transported to the sea surface microlayer by attaching to the bubble's interface. When the bubble eventually ruptures, a fraction of these particulates is often ejected into the surroundings in film droplets with a particulate concentration that is higher than in the liquid from which they formed. The precise mechanisms responsible for this enrichment are unclear, yet such enrichment at the ocean surface influences important exchange processes with the atmosphere. Here we provide evidence that drainage, coupled with scavenging, is responsible for the enrichment. By simultaneously recording the drainage and rupture effects with high-speed and standard photography, we directly measured the particulate concentrations in the thin film of a bubble cap at the moment before it ruptures. We observed that the enrichment factor strongly depends on the film thickness at rupture, and developed a physical model, based on scavenging and drainage, that is consistent with our observations. We have also demonstrated that this model is quantitatively consistent with prior observations of film drop enrichment, indicating its potential for a broader range of applications in the study of the sea surface microlayer and related phenomena.

The bubble-induced population dynamics of fermenting yeasts

“…Furthermore, during the peak of bubbling, when we zoomed in on the bubble layer-fluid medium interface (figure 4b) we noted yeast groups clinging to interfacial gas bubbles. These observations of yeast-bubble adhesion are very different from the reports of Walls & Bird [41].…”

Compound jetting from bubble bursting at an air-oil-water interface

“…Examples include the sea-surface microlayer on the ocean, or the microorganismenriched interface in the reaction tanks of municipal waste-water treatment plants 14,15 . Although some recent studies show that bubble bursting can disperse the surface organic layer as submicrometer droplets into water 16,17 or eject organic matter into the atmosphere through film droplets 18,19 , the capability of such a chemically complex interface to manipulate the bubble physics, particularly the jetting, remains largely unknown. In particular, jet droplets play an important role in the mass flux of bubble bursting aerosols 4 .…”

Water-to-air transfer of nano/micro-sized particulates: enrichment effect in bubble bursting jet drops

“…49 Meanwhile, for particles with r p > 0.1 µm, diffusive effects can also be neglected. 50 Additionally, the Stokes number (comparing the particle response time to the fluid characteristic time scales), St = (ρ p − ρ w )r 2 p u b /(9µR b ) with ρ p the particle density and u b the bubble velocity, of the particles in our experiments is < 10 −4 , indicating that the particles can be considered as inertialess, and follow the flow streamlines. Thus, the capture of suspended particles by the rising bubble is dominated by the interception mechanism.…”