From Individual Liquid Films to Macroscopic Foam Dynamics: A Comparison between Polymers and a Nonionic Surfactant

Area of Science:

• Colloid and Surface Science
• Materials Science
• Rheology

Background:

• Foam stability is crucial in various applications, yet macroscopic observations mask diverse microscopic origins.
• Understanding foam destabilization requires correlating macroscale behavior with microscale film dynamics.

Purpose of the Study:

• To compare macroscopic foam drainage and collapse with microscale thin-film dynamics.
• To elucidate the roles of surface stresses and intermolecular forces in foam stability.
• To differentiate the contributions of poly(vinyl alcohol) (PVA) and surfactant stabilizers.

Main Methods:

• Macroscopic observation of aqueous foam drainage and collapse.
• Microscale analysis of individual thin-film dynamics.
• Comparison of foams stabilized by partially hydrolyzed PVA and nonionic BrijO10 surfactant.

Main Results:

• Early-stage drainage is governed by distinct surface stress boundary conditions: PVA foams show higher stress capacity via Marangoni stresses and shear viscosity, while BrijO10 foams exhibit faster drainage due to weaker stresses.
• PVA foams display a unique homogeneous coalescence regime at longer times.
• Both foam types exhibit a universal, stabilizer-independent collapse mechanism characterized by a fast coalescence front propagation.

Conclusions:

• Stabilizer type significantly impacts early drainage via surface stress differences.
• Macroscopic foam stability is influenced by both microscale film dynamics and bulk properties.
• Foam collapse at later stages suggests a universal mechanism independent of specific stabilizer interfacial properties.