Factors Determining Number of Antifoam Entities in Foam Film

2 Factors Determining Number of Antifoam Entities in Foam Film 

Let us suppose then that antifoam entities do not adhere to bubble surfaces during their passage through the foaming liquid. Then N ir becomes eqnal to the number of antifoam entities present in the films separating bnbbles from the ambient air under conditions where they can, in principle, cause film rupture. As we have seen, such entities should bridge those films so that their diameters then approximate the thicknesses of the films at the point of rupture. 

A preliminary analysis of the factors contributing to the magnitnde of N, r may be readily obtained if we make some further simplifying assnmptions. Let ns assume therefore that the antifoam consists of monodisperse spheres, distribnted throughout the foaming liquid. The total number of monodisperse antifoam entities, N-, in a film of thickness h separating a bubble from ambient air is then given by the product of the number of antifoam entities per unit volume and the volume of the film. Thus, we can write 

It is reasonable to assume that A X b) is given by the number of antifoam entities remaining in foam films after they have drained to a thickness equal to the diameter of those entities. If foam film drainage occnrs at constant antifoam concentration, C , then we must have A X b) = Afp if / = in Equation 5.17 so that 

In using this eqnation to make numerical estimates of the magnitude of A Xrb), we note that mean antifoam drop radii in practical applications are typically 1 micron (see, e.g., references [7, 29]) and the average density of antifoams is reasonably approximated to within 10% as 10 g dm.  

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