A method of selecting foam inhibitors

Most foam inhibitors arc insoluble. A criterion is described for selecting foam inhibitors {from insoluble liquids3which form emulsions with the liquid to be defoamed. By determining the surface tensions of the liquid to be defoamed and of the additive saturated with that liquid and the interfacial tension between them, a rupture coefficient may be calculated. A high positive rupture coefficient is characteristic of a liquid with a high foam inhibiting ability for the specified foaming liquid. “A negative rupture coefficient is characteristic of liquids which will not reduce foaming. Fifty-four experimental cases are cited, for three foaming systems, to which the principle has been applied with high correlation. A mechanism of defoaming is described. Bubble coalescence rather than bubble rupture at the top of the foam is emphasized. It is shown that a spread film of a foam inhibitor on the surface of the foaming liquid may actually stabilize bubbles at the surface, although promoting rapid coalescence.