Foamed emulsion drainage: flow and trapping of drops

TL;DR

This paper investigates the aging process of foamed emulsions, focusing on drainage dynamics, drop trapping, and how oil influences foam stability and collapse.

Contribution

It provides a detailed analysis of foam aging regimes, revealing how oil drop dynamics affect drainage and foam stability over time.

Findings

Three distinct aging regimes identified

Oil drops become trapped and increase viscosity

Foam collapses due to oil acting as an antifoaming agent

Abstract

Foamed emulsions are ubiquitous in our daily life but the ageing of such systems is still poorly understood. In this study we investigate foam drainage and measure the evolution of the gas, liquid and oil volume fractions inside the foam. We evidence three regimes of ageing. During an initial period of fast drainage, both bubbles and drops are very mobile. As the foam stabilises drainage proceeds leading to a gradual decrease of the liquid fraction and slowing down of drainage. Clusters of oil drops are less sheared, their dynamic viscosity increases and drainage slows down even further, until the drops become blocked. At this point the oil fraction starts to increase in the continuous phase. The foam ageing leads to an increase of the capillary pressure until the oil acts as an antifoaming agent and the foam collapses.