Abstract
Stability factors of surfactant foam film are determined by several physical conditions depending on the thickness. Major driving forces in the drainage process are gravity, capillary pressure and surface tension, and the equilibrium film thickness is observed with a balance between the capillary pressure and the disjoining pressure. For a thick foam film, drainage progresses according to the hydrodynamic properties of the solution. Thermal fluctuation would occur during the drainage process, and a black film is finally formed after vigorous fluctuation. For a thin foam film, effects of the disjoining pressure, which can be expressed as the sum of the electrostatic double-layer force and the van der Waals force, would determine the foam film thickness. An air bubble in water would be considered hydrophobic by virtue of its high interfacial tension, thus raising the possibility of bubble coalescence. At the low concentration of surfactant, hydrophobic force plays an important role in bubble coalescence, while film elasticity is important at higher concentrations. The aim of this article is to review the research of single foam films from hydrodynamic and equilibrium points of view with using both horizontal and perpendicular foam film techniques. The effects of additives for foam film stabilization are then described.
