Bubble kinetics in a steady-state column of aqueous foam

TL;DR

This study investigates the dynamics of bubble size, speed, and liquid content in a steady-state aqueous foam column, revealing how bubbles evolve in size and shape due to diffusion and drainage, with a focus on size distribution transitions.

Contribution

It provides a detailed analysis of bubble evolution and size distribution in steady-state foam, explaining the phenomena through Laplace pressure differences and liquid fraction profiles.

Findings

Bubbles are nearly round at the bottom and grow larger as they rise.

The size distribution transitions from monodisperse to polydisperse with height.

An unexpected bidisperse regime occurs at intermediate heights.

Abstract

We measure the liquid content, the bubble speeds, and the distribution of bubble sizes, in a vertical column of aqueous foam maintained in steady-state by continuous bubbling of gas into a surfactant solution. Nearly round bubbles accumulate at the solution/foam interface, and subsequently rise with constant speed. Upon moving up the column, they become larger due to gas diffusion and more polyhedral due to drainage. The size distribution is monodisperse near the bottom and polydisperse near the top, but there is an unexpected range of intermediate heights where it is bidisperse with small bubbles decorating the junctions between larger bubbles. We explain the evolution in both bidisperse and polydisperse regimes, using Laplace pressure differences and taking the liquid fraction profile as a given.