Mixed aqueous-and-oil foams in bulk

Area of Science:

• Colloid and Surface Science
• Materials Science

Background:

• Particle-stabilised foams exhibit high stability and yield stress.
• Combining immiscible liquids is challenging but desirable for material innovation.

Purpose of the Study:

• To develop and characterize a stable composite foam system by mixing particle-stabilised aqueous and oil foams.
• To investigate the influence of component ratios and additives on composite foam stability and properties.

Main Methods:

• A mixed foam system was developed using olive oil foam (partially fluorinated particles) and aqueous foam (hydrophobic silica particles).
• The system was studied using bulk observations, confocal microscopy, and rheology.
• Variations in foam proportions, silica particle concentration, propylene glycol content, and sample age were analyzed.

Main Results:

• The composite foam demonstrated stability for over a week, resembling an emulsion of foams.
• Structure and flow properties were dependent on the proportions of constituent foams and additives.
• Foam phase inversion (water-in-oil to oil-in-water) was observed, influenced by silica wettability and dispersed foam concentration.
• Composites at the inversion point exhibited reduced stability and phase separation.

Conclusions:

• A stable, mixed-foam system capable of combining immiscible liquids was successfully developed.
• The study highlights the tunability of composite foam properties through compositional control.
• Understanding phase inversion is crucial for optimizing the stability of these novel foam materials.