Nonchiral Smectic Liquid Crystals

In this chapter, we describe the structure and properties of nonchiral smectic liquid crystalline phases. These phases are composed by achiral molecules and are characterized by both the long-range orientational order of molecular axes and a reduced positional order. They form stratified structures with a well-defined inter-layer spacing. The layers can slide over one another. Within each stratification, molecules can arrange in a variety of ways leading to various types of smectic phases that are designated as smectic A (Sm A), smectic B (Sm B), smectic C (Sm C), …., smectic J (Sm J) and smectic K (Sm K). Based on the layer structure non-tilted (orthogonal) and tilted have been distinguished. In the orthogonal phases, director remains perpendicular to the layer normal whereas in tilted phases director (or molecules), on the average, is tilted with respect to the layers. These phases differ from each other in the kind and extent of their order, symmetry and layer formation. Based on the ordering of layers, three smectic types are identified: smectics with liquid layers, bond-orientational order and ordered layers. The characteristic features, synthesis and properties of nonchiral smectic mesophases are described.