Hexagonal symmetry for smectic blue phases

Smectic blue phases are liquid crystalline phases which exhibit both three-dimensional-orientational order and smectic positional order. X-ray scattering experiments reveal that at least one of these phases is not cubic, as classical blue phases, but offers a hexagonal symmetry. A comparison of the experimental patterns with the scattering patterns given by smectic double twist tubes sketched by Kamien is proposed.