Drainage of particle stabilized foam film

Abstract

Abstract A model for drainage of aqueous foam film with a partial coverage of particles accounts for an inner clean air-liquid film surrounded by a film stabilized by close packed particles at the outer periphery. The drainage of the inner film occurs due to capillary pressure gradient. The film thickness is found to decrease fastest at the center with the inner film being thinner than the outer film eventually leading to its rupture as a result of film thickness becoming zero at the center. The velocity of film drainage is found to be higher for lower particle concentration and higher surface tension. The lifetime (time of rupture) of the film is found to be larger for larger bubble size and liquid holdups (higher initial film thickness). For a film stabilized by close packed monolayer or multilayer of particles, the disjoining pressure is larger for larger particle number concentration and particle size, increases with surface tension only for film stabilized by single or two layers of particles and is a function of bubble size only for film stabilized by multilayers of particles. The maximum disjoining pressure decreases with contact angle approaching zero for a critical contact angle of 129° and increases linearly with surface tension. At mechanical equilibrium, the particle stabilized foam gets drier for larger bubble sizes, contact angles and particle number concentrations.