Critical capillary pressure for destruction of single foam films and foam: effect of foam film size

Foams and single foam films stabilised by ionic and amphiphile polymer surfactants are studied with foam pressure drop technique (FPDT) and thin liquid film-pressure balance technique (TLF-PBT). A pressure is reached at which the single foam films rupture and the foams destruct very fast (avalanche-like). For film rupture we named this pressure—critical capillary pressure of film rupture, Pcr,film while for foam destruction, we introduced a new parameter—critical capillary pressure of foam destruction, Pcr,foam. The surfactant kind and foam film type (common thin, common black and Newton black) affect the values of both parameters. When below 20 kPa, Pcr,film and Pcr,foam are close by value, when over 20 kPa, there is a significant difference between them. The Pcr,film versus film size and Pcr,foam versus foam dispersity dependences, indicate that the film size and foam dispersity strongly affects the critical capillary pressure values. Film size distribution histograms reveal that a foam always contains films that are of a larger than the most probable size. They rupture at lower pressures, does initiating the destruction of the whole foam, which can be an explanation why higher than 20 kPa there is a difference between Pcr,film and Pcr,foam values. This parameter, Pcr,foam is considered of significant with respect to foam stability and could find use in industry.