Tunable effective diffusion of CO₂ in aqueous foam

Area of Science:

• Colloid and Surface Science
• Materials Science
• Chemical Engineering

Background:

• Aqueous foams possess large gas/liquid surface areas, facilitating dynamic fluid component exchange.
• Binary-gas foams, with bubbles containing two gases of differing liquid affinities, present opportunities for cost-effective gas separation.
• Foam structure evolution in single-gas systems is governed by Ostwald ripening due to Laplace pressure differences.

Purpose of the Study:

• To investigate the structural evolution of carbon dioxide (CO2)-laden 2D foams exposed to air.
• To develop a model describing gas diffusion and transport within binary-gas foams.
• To explore the potential for tunable gas retention and release in foams.

Main Methods:

• Experimental investigation of CO2-laden 2D foams exposed to air.
• Derivation of a nonlinear diffusion model for gas transport in foams.
• Modeling foams as effective homogeneous media using gas permeability ratios.

Main Results:

• Observed a crust of small bubbles forming at the foam front during CO2-air exposure.
• Developed an effective medium model where gas diffusivity depends on foam structure and film permeability.
• Demonstrated that effective diffusivity can be tuned between liquid and atmospheric diffusion limits.

Conclusions:

• Binary-gas foam evolution is influenced by partial pressure differences, in addition to capillary effects.
• The gas permeability ratio across soap films is critical for controlling gas transport.
• Foam systems offer tunable gas retention and release capabilities by manipulating atmospheric composition.