The mechanisms of antifoam action

The homogeneous and heterogeneous mechanisms of antifoam action are examined. The homogeneous mechanism involves the adsorption displacement of the molecules of the foam-forming agent from the surface layers of foam films with formation of mixed layers of the foam-forming agent and the antifoam; in this case, the foam films are in a nonequilibrium state. The heterogeneous mechanism of the destruction of the foam consists in the formation of unstable asymmetric aqueous films and the subsequent appearance, after their disruption, of 'bridges' consisting of drops or solid particles of the antifoam passing through the foam film. It is shown that the most important factors governing the instability of the asymmetric film are the low degree of adsorption of the foam-forming agent on the interface between the films and the drops of the antifoam and the solid particles, as wellas the presence of rough regions on the solid particles. The antifoam action of solid particles or drops forming the 'bridges' is determined by the wetting angles. The foam film is ruptured when the establishment of an equilibrium three-phase foam film-antifoam-gas contact is impossible. In many systems, both mechanisms of the destruction of the foam operate simultaneously. The bibliography includes 66 references.