The deformation of soap film junctions by applied forces

The equilibrium configuration of soap films in a tetrahedral frame is well known, and a study is reported here of the displacement of the tetrahedral vertex formed at the junction of the Plateau borders between the films. Applying a force to this junction causes an increase in soap film area, and hence surface energy, which is modelled both theoretically and numerically. In the present work, this force is conceived as being due to the displacement of a small particle at the centre of the vertex and the energy dependence of the configuration on both the size of the particle and the magnitude of the displacement is calculated. The results underline the importance of the curvature of the films in any detailed analysis of the suspension of particles in a foam, as, for example, in the industrial process of foam flotation. The results are relevant also to problems of foam drainage and stability.