The Science of Defoaming

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5

Effect of Antifoam

Concentration on

Volumes of Foam

Generated by Air

Entrainment in

Aqueous Solutions

5.1 PHENOMENOLOGY

5.1.1 inTroducTion

For a given antifoam–surfactant solution combination, the main practical concern

is simply to ensure that sufcient antifoam is present to produce the desired dimi-

nution in foam volume given the nature and intensity of the relevant aeration pro-

cesses involved. If this is to be achieved with a minimal level of empiricism, some

knowledge of the relation between antifoam concentration and foam volume under

given conditions of foam generation is required. Despite the evident importance of

this fundamental aspect of antifoam behavior, there have been relatively few attempts

to understand it [1]. This of course derives from the complexity that we have shown

characterizes the overall process of antifoam action on foam volume. We may, how-

ever, derive useful generalizations if we make some simple, but realistic, assumptions.

Let us conne our generalizations to the effect of antifoam on the generation of

foam (i.e., to measurements of foamability) without making reference to the stability

of the resulting foam. Control of foamability is after all often the primary function of

antifoams. Inconvenient consequences accompanying the formation of large quanti-

ties of unwanted foam are not always effectively ameliorated by a gradual collapse of

that foam over a period of several minutes (or even seconds)! We are therefore par-

ticularly concerned here with foam generation by air entrainment where foam is pro-

duced during shaking, rotation, stirring, plunging, or by impinging jets. It is arguable

that many, if not most, foam control problems are caused by such air entrainment.

Antifoams are often conveniently dispersed into foaming systems in the form

of emulsion drops or individual particles. Here we assume that the concentration,

state of dispersion and the effectiveness of each antifoam entity in such antifoam

dispersions remain constant during foam generation. These assumptions therefore