This destroys the helical structure and the light cannot be transmitted. At certain temperatures, generally below the nematic phase, the liquid crystal material may gain an amount of positional order . Within each layer the liquid crystal is essentially a 2 dimensional nematic liquid crystal. There are many types of smectic materials and Figs. 5-7 show just three examples.
Smectic materials have potential advantages over nematics when used in liquid crystal displays.
They exhibit better viewing angle characteristics, contrast ratio and can operate at high speed. Most of the work in our group concerns such materials. There also exists higher order smectics which form layers with positional ordering within the layers . For instance in smectic B materials the molecules in each layer for a hexatic structure. In a similar way to chiral nematics there are chiral forms of smectic phases.