The relationship between the surface and internal structure of dry foam

Abstract

This paper explores the relationship between the surface and underlying structure of dry foams by means of simulation. This is used as the basis for statistically predicting the surface bubble size distribution based on the measurement of the surface film size distribution. The reason for carrying out this study is because most foam systems are opaque or semi-opaque making the direct measurement of the internal structure difficult. Researchers and engineers typically used the size distribution of the films observed at the foam surface as a proxy for the bubble size distribution. By simulating realistic foam structures with free surfaces, the statistical properties of these surfaces were obtained and analysed. It is shown that for a given surface bubble size there is a distribution of possible surface film sizes. The distribution of the ratio of the film size to the bubble size is found to be independent of the underlying bubble size distribution for the range of poly-dispersities studied in this paper. This distribution for the ratio of film to bubble size allows the size distribution for the surface bubbles to be predicted using the distribution of film sizes visible at the foam surface.