Absorptive limits of foams governed by kinematic coupling between solution and bubbles

Abstract

Hypothesis: Foams exhibit absorptive properties and are widely used for cleaning contaminants, oil recovery, and selective mineral extraction via froth flotation. Although foam absorption has historically been linked to equilibrium osmotic pressure, empirical observations show that drainage occurs at levels much lower than theoretical predictions. Here we investigate the physical origin of the absorptive limit of the foams. Experiment: We mainly used 5.0 wt% solution of ionic surfactant TTAB (tetradecyltrimethylammonium bromide). The foam was placed inside the Hele-Shaw cell, which was then positioned vertically. We observed whether the solution is drained or not with changing the foam height and the liquid fraction. We also observed the rearrangement of the internal bubbles. Findings: While foams have traditionally been modeled as immobile porous media, the reality involves kinematic coupling between the solution flow and the bubbles, which establishes local rearrangements of the bubbles as the key factor in determining effective osmotic pressure. This framework is most fundamental for the dynamics of soft jammed systems, such as blood flow in vessels, emulsions, and biological tissues, offering significant advancements in the understanding of soft jammed system behaviors.