2D Smectic of a T-shaped Liquid Crystal Mesogen*

We report structural studies of a T-shaped mesogenic molecule. Upon cooling from the isotropic, the molecules first form a lamellar phase, with the molecular tails organized into sheets and the head groups isotropic in the plane of the lamellae. On further cooling, the head groups self-assemble into phases with 2D nematic and smectic order. The 2D smectic has only short-range positional correlations, with dislocations in the layering. The development of the 2D smectic reduces the long-range correlations of the fundamental lamellar structure, with the system evolving into a biaxial nematic with the T-shaped molecules ordered in three dimensions but with only short-range correlations.