ABSTRACT
Antifoams are usually largely composed of oils that are present as undissolved drops in foaming solutions. The presence of oils in the form of undissolved drops is not, however, a sufficient requirement. Thus, it has often been proposed that such oils should also have the property of emerging into the surface of the foaming liquid, which implies that the films separating that liquid phase from the relevant gas phase should be intrinsically unstable. These asymmetric films are the so-called pseudoemulsion films, first named by Wasan et al. [1]. In addition, it has also been proposed that the emerged oil should spread over the gas-liquid surface of the foaming liquid (see, e.g., references [2-6]). The first proposal that spreading is associated with antifoam behavior was in fact made by Leviton and Leighton [7] more than seven decades ago. Subse quently there have been numerous attempts to correlate the antifoam behavior of undissolved oils with their spreading behavior [4, 8-14]. Underlying much of this work has been the concept that spreading oil drops at gasliquid surfaces produce shear forces in foam films, leading to the rupture of those films.
