Chain and ring structures in smectic phases of molecules with transverse dipoles

Systems of hard spherocylinders with central transverse point dipoles are studied by Monte Carlo simulation. The dipoles are seen to stabilise the formation of the smectic-A phase relative to the nematic phase; the nematic phase disappears altogether at low temperatures. In the smectic-A phase the cores of the molecules align parallel to the layer normal with the dipoles in the plane. At high temperatures the dipoles are orientationally disordered; as the temperature is lowered ring-like domains appear, and then elongated antiferroelectric chain-like domains form. We analyse these results in the context of recent studies on two-dimensional vortex-antivortex systems.