Bubble columns that produce foam are commonly found in waste water treatment and other industrial processes. The head on a glass of beer is another familiar example of foam formed by bubbles rising through a liquid and collecting on the surface. The characteristics of the foam that is formed in these systems such as the foam height, density and lifetime are all dependent on the properties of the surface-active compounds that are present in the liquid.
In the present work, a fundamental study of single bubble interactions at a planar air-liquid interface is performed. When a single bubble moves upward and reaches the interface, a thin film of liquid is formed that drains and eventually ruptures. The volume of liquid entrained in this film is important in determining the properties of the resulting foam. For example, thicker films will tend to produce “wetter”, more dense foams. A thicker film may also take longer to drain and therefore result in taller foam heights and/or more stable foams. Using interferometry, the volume of liquid entrained in the film is measured for several different surfactant systems. The properties of the surfactants, including interfacial rheological properties, are then related to the volume of fluid entrained in the film.