Foam drainage placed on a thin porous layer.

Area of Science:

• Colloid and Surface Science
• Materials Science
• Biomedical Engineering

Background:

• Foam drainage on porous substrates is crucial for applications like drug delivery.
• Previous theories primarily focused on thick porous substrates.
• Foam applications on skin and hair involve thin porous layers.

Purpose of the Study:

• To develop a theory for foam drainage on thin, completely wettable porous layers, incorporating surface viscosity.
• To predict foam drainage rates, imbibition, and the formation of a free liquid layer.
• To compare theoretical predictions with experimental observations.

Main Methods:

• Developed a theoretical model combining foam drainage equations with imbibition into a thin porous substrate.
• Incorporated the effect of surface viscosity, leading to an "effective slip" at the liquid-air interfaces.
• Compared theoretical predictions with experimental data from foam drainage on thin porous layers.

Main Results:

• The theory accurately predicts foam drainage and imbibition rates on thin porous layers.
• Surface viscosity was shown to increase the movement of the foam's top boundary.
• Three distinct regimes of the spreading/imbibition process were predicted, including conditions for free liquid layer formation.

Conclusions:

• The developed theory provides a reliable framework for understanding foam drainage on thin porous layers.
• Surface viscosity plays a significant role in foam dynamics and can be leveraged for applications.
• The findings support the potential of foam-based systems for effective drug delivery and other applications.