Size Amplification of Jet Drops due to Insoluble Surfactants

TL;DR

This study investigates how insoluble surfactants influence jet drop size during bubble bursting, revealing a reversal in trend for small bubbles and highlighting implications for aerosol distribution in contaminated environments.

Contribution

It uncovers the effect of insoluble surfactants on jet drop formation, showing a trend reversal due to Marangoni stresses, supported by experiments and simulations.

Findings

Surfactants increase drop size in small bubbles without precursor waves.

Marangoni stresses focus collapsing cavities, altering drop ejection.

Quantitative agreement between experiments and simulations.

Abstract

Surface bubbles in the environment or engineering configurations, such as the ocean-atmosphere interface, sparkling wine, or during volcanic eruptions typically live on contaminated surfaces. A particularly common type of contamination is surface active agents (surfactants). We consider the effect of insoluble surfactant on jet drop formation by bubble bursting. Contrary to the observed trend that surfactants decrease the ejected drop radius for bubbles with precursor capillary waves, we find that surfactants increase the ejected drop radius for bubbles without precursor capillary waves - a regime characteristic of small bubbles. Consequently, the results have fundamental implications for understanding aerosol distributions in contaminated conditions. We find that the trend reversal is due to the effect of Marangoni stresses on the focusing of the collapsing cavity. We demonstrate quantitative agreement on the jet velocity and drop size between laboratory experiments and numerical simulations by using the measured surface tension dependence on surfactant concentration as the equation of state for the simulations. *Jun Eshima and Tristan Aur\'egan contributed equally to this work.