Hexagonal mesophases: Honeycomb, froth, mesh or sponge?

The mesostructure of hexagonal phases in lyotropic liquid crystals and some inorganic derivates is reconsidered in topological terms, and it is argued that related rhombohedral sponge and mesh structures may well form in the vicinity of a conventional hexagonal phase. The standard signature of a hexagonal phase from small-angle scattering patterns is insufficient evidence for the hexagonal honeycomb arrangement of one-dimensional channels believed to characterize the mesostructure, and an alternative swelling analysis is suggested to offer a more detailed probe of film topology in hexagonal systems.