An experimental realization of the Weaire–Phelan structure in monodisperse liquid foam

The Weaire–Phelan (WP) structure is the lowest energy structure known of an ideal monodisperse foam in the dry limit. To date, it has not been realized in the laboratory. Instead Lord Kelvin's 1887 structure, which it supplanted in 1994, has repeatedly been found in attempts to produce an ordered structure. This paradox is attributable to the flat walls of the containers used, with which the Kelvin structure is more compatible. Accordingly, we have fabricated a patterned mould whose faceted walls conform to the WP geometry, and thereby succeeded in inducing the formation of perfect crystals of the WP structure. Foam samples consisted of approximately 1500 bubbles. Vibrations favoured crystallization.