Marginal regeneration-induced drainage of surface bubbles

TL;DR

This study visualizes marginal regeneration patches on soap bubbles, demonstrating their significant role in bubble film drainage and lifetime, especially in humid environments without evaporation.

Contribution

It provides the first detailed visualization and quantification of marginal regeneration patches and confirms their dominant role in bubble film thinning.

Findings

Rising velocities and sizes of patches match theoretical models.

Drainage due to patches explains bubble thinning in humid conditions.

Marginal regeneration controls film thinning when evaporation is negligible.

Abstract

The prediction of the lifetime of surface bubbles necessitates a better understanding of the thinning dynamics of the bubble cap. In 1959, Mysel \textit{et al.} \cite{mysels1959soap}, proposed that \textit{marginal regeneration} i.e. the rise of patches, thinner than the film should be taken into account to describe the film drainage. Nevertheless, an accurate description of these buoyant patches and of their dynamics as well as a quantification of their contribution to the thinning dynamics is still lacking. In this paper, we visualize the patches, and show that their rising velocities and sizes are in good agreement with models respectively based on the balance of gravitational and surface viscous forces and on a Rayleigh-Taylor like instability \cite{Seiwert2017,Shabalina2019}. Our results suggest that, in an environment saturated in humidity, the drainage induced by their dynamics correctly describes the film drainage at the apex of the bubble within the experimental error bars. We conclude that the film thinning of soap bubbles is indeed controlled, to a large extent, by \textit{marginal regeneration} in the absence of evaporation.