Orthogonal hexatic smectic phase-rare or common?

The hexatic smectic B (Hex B) phase is commonly encountered among hydrogen-bonded liquid crystal materials. Among enaminoketone and Schiff's base compounds, twenty homologous series (c. 10² compounds) exhibiting orthogonal mono-or bi-layer hexatic phases were identified by combined microscopy and DSC. Phase transitions from crystal B (CrB) of S_f to Hex B as well as from Hex B to S_f, S_a or S_c phases were observed within the range 50 to 190°C. Temperature ranges of the Hex B phase detectable by DSC varied from 0.2 to 20°C. Within two groups of three-ring enaminoketones, the formation of the Hex B phase was found to be controlled by both inductive and mesomeric components of the Hammett constants of the terminal substituents of the molecules.