Influence of surfactant concentration on drop production by bubble bursting

TL;DR

This study investigates how surfactant concentration affects drop production during bubble bursting, revealing that surfactants significantly alter drop size, number, and formation dynamics, which impacts sea spray aerosol predictions.

Contribution

It experimentally demonstrates the influence of surfactant molecules on bubble collapse and drop formation, highlighting effects beyond simple surface tension reduction.

Findings

Surfactants reduce the number and size of drops produced.

Surfactants can prevent drop formation at certain concentrations.

Effects are mainly due to Marangoni stresses, not just surface tension lowering.

Abstract

Bubble bursting at the surface of the sea water produce drops and is the main source of sea spay aerosol. The mechanisms underlying the drops production from a single bubble bursting event have been intensively studied and the influence of the bubble size and liquid parameters (density, viscosity and surface tension) has been unified. However, despite the diversity of the surfactant molecules present in the oceans, their influence has been overlooked. In this paper we experimentally explore the influence of the surfactant concentration (Sodium Dodecyl Surfate - SDS) in a water solution on a single bubble collapse and subsequent drop production. We show that these surfactant molecules have an astonishing effect. In particular, we quantitatively show that they modify the bubble collapse, they induce less, smaller and faster drops and they can even completely prevent the drop production for a particular concentration. These results are presented in the existing dimensionless framework and they allow us to affirme that these effects are mainly a consequence of the surface tension gradients (Marangoni stresses) more than just the surface tension lowering. Finally, this study shows that the role of water contamination by surface-active agents is important and needs to be understood to improve the prediction of the sea spray aerosol.