Foam stability: Part III. Spontaneous foam destabilization resulting from gas diffusion

Abstract

AbstractBubble size frequency distributions in foamed Tee‐pol solutions, oil‐in‐water emulsions and Hevea rubber latex have been calculated from the observed bubble sizes in the plane of contact between the foam and the glass wall of the container. The bubble size distribution in these foams can be satisfactorily described by the same mathematical expression containing one adjustable parameter.Using this expression for the distribution function, a relation is derived between the total number of bubbles per unit area of the cross‐section and the age of the foam, assuming that the disappearance of the small bubbles is caused only by transfer of gas to larger bubbles. With the aid of the derived relationship the average thickness of the liquid lamellae in a number of foams is calculated from the observed rate of decrease in the number of bubbles in the front layer.The calculated values of the average film thickness are of the same order of magnitude as those calculated directly from the observed bubble size distribution and the liquid content of the foam. Additional evidence of the proposed destabilization mechanism is obtained from experiments, in which the nature of the gaseous phase was varied and from comparison of the rate of decrease in the number of bubbles with the rate of shrinking of individual bubbles.