ABSTRACT
The smectic B phases, to be considered in this chapter, belong to the family of ordered smectics. Their common features are that the molecules are oriented along the layer normal and that they exhibit hexagonal symmetry [2-7]. As a consequence, they are optically uniaxial. However, it has long remained undecided whether they were real crystals or just stackings of crystallized layers, uncorrelated one with the other, as proposed by de Gennes and Sarma in 1972 [8]. Today we know that they are real three-dimensional crystals, but highly sophisticated X-ray scattering experiments were needed to prove this result conclusively [9, 10]. Consequently, from a structural point of view, these phases are fundamentally different from the hexatic phases, which lack a long-range positional order. They do, however, exhibit some physical properties similar to hexatic phases, and even to more fluid phases such as the smectic A. We shall see, for instance, that the smectic B exhibits a layer buckling instability, analogous to the one encountered in smectics A. On the other hand, as far as their interfacial and growth properties are concerned, they are much closer to ordinary crystals than to fluid phases.
