Coarsening of bubble assemblies: From dry foams to dilute bubbly liquids

Experimental data on bubble coarsening in a liquid are sparse, limited to relatively narrow ranges of liquid volume fractions, and do not encompass the full range relevant to the numerous applications of these systems. Our objective is to leverage recent data obtained aboard the International Space Station and to integrate these with dedicated measurements to produce a comprehensive coarsening rate diagram across the entire range of liquid fractions.

The objective of new coarsening measurements is to eliminate gravity effects, which can make these systems highly inhomogeneous. We achieve this by using clinostat-type coarsening cells capable of maintaining the homogeneity of foams with low aqueous solution content, i.e. between 2% and 8%. For liquid fractions above 45%, we replace the aqueous solution with a concentrated emulsion of oil droplets in an aqueous solution, possessing a low yield stress to counteract gravitational effects without impacting coarsening kinetics.

For the first time, by combining our results with recent data obtained aboard the International Space Station using the same surfactant, we achieve coverage of the full range of liquid fractions characterizing liquid foam coarsening, from 2% to 38%, significantly expanding the range studied to date. This leads us to propose a model that describes coarsening over this entire range, accounting for both osmotic pressure effects and contact adhesion effects at higher liquid fractions. Similarly, for the first time, we have data covering the full range of liquid fractions characterizing the coarsening of bubbly liquids, from 45% to 96%, allowing us to compare existing models and identify the most robust ones. Finally, we can map the evolution of coarsening rates over a broad range, from 2% to 96%, thereby highlighting the overall impact of dispersed phase fraction on coarsening. This provides a valuable new tool to tackle coarsening effects in diphasic systems.