Foam coarsening in granular packings.

Area of Science:

• Materials Science
• Fluid Dynamics
• Colloid Science

Background:

• Foam coarsening, the increase in bubble size due to gas diffusion, alters foam properties.
• Understanding foam behavior in confined spaces like porous media is critical for applications.
• Existing models often do not fully capture the complexities of confined foam dynamics.

Purpose of the Study:

• To investigate the coarsening dynamics of liquid foam confined within spherical grain packings.
• To determine the influence of liquid fraction and grain size on confined foam coarsening rates.
• To develop and validate a model that accurately predicts coarsening under confinement.

Main Methods:

• Systematic variation of grain size and liquid fraction (7-25%) in confined foam experiments.
• Experimental observation of foam coarsening dynamics within a granular medium.
• Development of a model based on effective liquid fraction to describe observed dynamics.

Main Results:

• Confined foam coarsening rate shows reduced sensitivity to liquid fraction compared to bulk foams.
• The ratio of bubble size to grain size emerges as a dominant factor governing coarsening dynamics.
• A model incorporating effective liquid fraction successfully captures the experimental observations.
• Observation of persistent small bubbles at liquid bridges, acting as accumulation sites.

Conclusions:

• The effective liquid fraction is a key parameter for modeling foam coarsening under confinement.
• Bubble-to-grain size ratio significantly influences coarsening rates in porous media.
• The presence of liquid bridges and associated small bubbles impacts foam stability and evolution in confined systems.