ABSTRACT
Several antifoaming mechanisms may be proposed in the literature and the most suggested mechanism may be bridging mechanisms by several types of antifoams. In the last step of foam breaking, the capillary force dewets the film from the oil or solid bridge and the film then ruptures. Dippenaar performed a direct observation of solid particles by a cinematographic approach [206, 207]. Garrett [208], Frye and Berg [205], and Aveyard et al. [211] also did discuss the mechanism of rupture in view of Dippenaar’s work and the thermodynamics of the systems from the viewpoint of contact angle. The antifoaming efficiency strongly depends on the stability of the pseudoemulsion film. The stability of the pseudoemulsion film was directly studied by Wasan et al., forming such a film from a surfactant solution on the tip of a capillary [182, 189]. They pointed out that the edge of the particles penetrating into an aqueous phase can pierce and break the pseudoemulsion film. Furthermore, the particle concentration required to break the foam film is very low, because it is sufficient that the film be pierced at only one point to rupture. We have tried to directly clarify the mechanism of breakdown of such films and correlate it to the defoaming efficiency of different types of antifoaming particles using laser microscopic techniques.
