Optical Tomography of Real Three-Dimensional Foams

Optical tomography has been implemented as a nondestructive method for investigating the structure of real three-dimensional polyhedral soap foams. Images of successive slices of the transparent foam are obtained by means of a CCD camera equipped with a very thin depth-of-field objective, and the coordinates of the foam vertices are determined. The 3D foam is then numerically reconstructed using surface energy minimization software to calculate the volume, the area, and the isoperimetric quotient of each bubble. This optical tomography has been used on a four bubbles thick layer of foam at two different capillary pressures in order to get a dry foam and a wet foam with similar topology. The evolution of the foam morphology upon drainage has been investigated. The network of the Plateau borders of the wet foam was also reconstructed, assuming that the Plateau borders are like prisms and the vertices are like octahedra. If the liquid volume is neglected in the films, the liquid fraction of the wet foam can be directly evaluated.