Stability of draining plane-parallel films containing surfactants

Area of Science:

• Fluid dynamics
• Surface science
• Thin film stability

Background:

• Partially mobile draining thin liquid films are crucial in various industrial processes.
• Understanding film rupture dynamics is essential for predicting product stability and performance.
• Existing models often simplify interfacial properties and their impact on stability.

Purpose of the Study:

• To analyze the stability of partially mobile draining thin liquid films against axisymmetric fluctuations.
• To investigate the influence of interfacial material properties on film rupture.
• To differentiate between critical thicknesses for stability loss, transition, and rupture.

Main Methods:

• Application of lubrication approximation for long wave stability analysis.
• Consideration of coupling between drainage and perturbation flows.
• Examination of radially-bounded and unbounded wave modes.
• Comparison of linear and non-linear theoretical predictions.

Main Results:

• Demonstrated distinct critical thicknesses: h(st) > h(tr) > h(cr).
• Interfacial mobility has minimal impact on draining film rupture thickness.
• Interfacial tension and disjoining pressure are key factors determining critical rupture thickness.
• Electromagnetic retardation in van der Waals interactions plays a significant role.

Conclusions:

• Theoretical predictions align well with experimental data for foam and emulsion films.
• The study provides a more nuanced understanding of thin film rupture mechanisms.
• Highlights the importance of interfacial properties and van der Waals forces in film stability.