Flowing Menisci: Coupled Dynamics and Liquid Exchange with Soap Films

Area of Science:

• Fluid dynamics
• Materials science
• Soft matter physics

Background:

• Liquid foams feature menisci that thin under gravity, reaching a steady state where hydrostatic and capillary pressures balance.
• Existing drainage models for foam menisci often overlook liquid exchange with adjacent soap films, assuming negligible liquid reservoirs.

Purpose of the Study:

• To systematically measure the shape of an isolated meniscus within a vertical soap film under varying conditions.
• To develop an extended drainage model that accounts for liquid flux from soap films into menisci.
• To introduce and define a gravito-exchange length governing minimum meniscus thickness.

Main Methods:

• Controlled experiments were conducted to measure the shape of isolated menisci in vertical soap films.
• Systematic variation of film thickness was employed to identify different flow regimes.
• An analytical model was developed to incorporate dynamical liquid exchange effects into the standard drainage equation.

Main Results:

• A flowing regime was identified where increased soap film thickness significantly enlarges the meniscus due to liquid flux.
• The developed analytical model quantitatively agrees with experimental observations.
• The model successfully captures the transition between hydrostatic and flowing meniscus behaviors.

Conclusions:

• Liquid exchange between soap films and menisci is a significant factor influencing meniscus thickness in liquid foams.
• The newly introduced gravito-exchange length provides a critical parameter for understanding minimum meniscus thickness.
• The findings have implications for understanding the behavior of flowing or rearranging foams, particularly those with thick films.