Experiments on soap films in Plateau frames: pre-emptive topological transitions

Abstract

We report on an experimental study of the film configurations in prismatic Plateau frames of number of lateral faces n between 3 and 6, and different aspect ratios h/a (h = frame height; a = base side length). The upper base of a frame is a string around the lateral metallic sides, parallel or inclined to the lower horizontal base. Pre-emptive topological transitions from the configurations with an n-sided planar film inside the frames were observed for all n values, which occur under increasing h/a at a critical value which in turn increases with increasing n. For n = 6, two different topologies may appear following the pre-emptive disappearance of the hexagonal film. At low h/a, instead of an inner n-sided film, the configuration observed is similar to an uncovered box with a film at the metallic base and n rectangular films at the n lateral faces of the frame. Transitions in the reverse direction, ending at a planar n-sided film, also occur pre-emptively. For n = 4 and large h/a, a (closed) bubble forms along the top of the resulting rectangular vertical film, itself formed by flipping of the horizontal square film.