Studies on Foam Films

Most quantitative studies on foams have been carried out using foam films. As discussed above, microscopic horizontal films were studied by Scheludko and 

One of the most important characteristics of foam films is the contact angle 0 that appears where the film makes contact with the bulk phase (solution) from which it is formed. This angle can be obtained using a topographic technique (that is suitable for small contact angles) which is based on determination of the radii of the interference Newton rings when the film is observed in a reflected monochromatic light. 

Another technique used to study foam films is a-particle irradiation, which can destroy the film. Depending on the intensity of the a-source, the film will either rupture instantaneously or live for a much shorter time than required for its spontaneous rupture. The lifetime of a black film subjected to irradiation is considered as a parameter characterizing the destructive effect of a-particles. 

A third technique for studying foam films is the fluorescence recovery after photobleaching (FRAP). This techniques was applied by Clarke et al. [36] for lateral diffusion in foam films, and involves irreversible photobleaching by intense laser light of fluorophore molecules in the sample. The time of redistribution of probe molecules (which are assumed to be randomly distributed within the constitutive membrane lipids in the film) is monitored. The lateral diffusion coefficient, D, is calculated from the rate of recovery of fluorescence in the bleaching region due to the entry of unbleaching fluoroprobes of adjacent parts of the membranes. 

Deryaguin and Titijevskaya [37] measured the isotherms of disjoining pressure of microscopic foam films (common thin films) in a narrow range of pressures. At equilibrium, the capillary pressure in the flat horizontal foam film is equal to the disjoining pressure n in it, 

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