Scraping of foam on a substrate.

Area of Science:

• Soft matter physics
• Rheology
• Colloidal science

Background:

• Foams are critical soft jammed systems with industrial applications.
• Foam rheology is influenced by the interplay between gas bubbles and liquid.
• Understanding foam behavior is essential for optimizing its use.

Purpose of the Study:

• To investigate the scraping dynamics of foam by a rigid plate.
• To elucidate the coupling effects between gas bubbles and liquid on foam rheology.
• To develop a theoretical framework for foam scraping behavior.

Main Methods:

• Utilized a 5.0 wt% solution of ionic surfactant tetradecyltrimethylammonium bromide (TTAB).
• Systematically varied parameters including scraping velocity, gap height, confinement length, foam volume, and substrate wettability.
• Observed and analyzed foam scraping patterns.

Main Results:

• Identified three distinct scraping patterns: homogeneous, no scraping, and slendered.
• Observed behaviors significantly differ from those of simple liquid systems.
• Developed a theoretical model for the homogeneous scraping limit based on dewetting and shear competition.

Conclusions:

• The study provides new insights into foam rheology and scraping dynamics.
• The developed theory successfully explains the upper limit of homogeneous scraping.
• The theoretical framework is applicable to other soft jammed systems, including colloidal and emulsion suspensions.