Quantitative description of foam drainage: transitions with surface mobility

Area of Science:

• Colloid and Surface Science
• Fluid Dynamics
• Materials Science

Background:

• Aqueous foams are ubiquitous in nature and industry.
• Foam drainage, the process of liquid removal, is crucial for foam stability and performance.
• Understanding foam drainage mechanisms is essential for controlling foam properties.

Purpose of the Study:

• To investigate the influence of bubble size and surface properties on foam drainage.
• To identify key parameters controlling foam permeability and drainage regimes.
• To develop a unified model for foam drainage across various experimental conditions.

Main Methods:

• Forced drainage experiments were conducted on aqueous foams.
• Bubble diameters (D) were varied from 0.18 to 8 mm.
• Foams were prepared using solutions with diverse surfactant and protein compositions to alter surface viscoelasticity.

Main Results:

• Two distinct foam drainage regimes were identified, dependent on bubble size and surface properties.
• A single surface mobility parameter was found to effectively incorporate bubble size and surface properties.
• Permeability measurements revealed the relationship between foam channel/node hydrodynamic resistance and surface mobility.
• Anomalous drainage behaviors were observed for the smallest bubbles (D < 0.5 mm).

Conclusions:

• The surface mobility parameter provides a consistent description of foam drainage regimes and their transitions.
• Hydrodynamic resistances in foam channels and nodes are strongly influenced by surface mobility.
• The findings offer a simplified yet comprehensive understanding of aqueous foam drainage dynamics.