CHARACTERIZATION OF THE HEXATIC-B AND CRYSTAL B-PHASES BY OPTICAL MICROSCOPY

Recent investigations concerning the structure of the B phase have unearthed a variety of packing arrangements of the molecular layers for this smectic modification. Two general structures have been discovered; one in which the B phase has three-dimensional crystalline order (crystal B), and one that is characterized by short-range in-plane positional ordering of the constituent molecules, and long-range bond orientational order, both within and between the layers (hexatic B). In this present study n-hexyl 4 prime -n-pentyloxybiphenyl-4-carboxylate (650BC) has been synthesized and its smectic phases characterized. Typically, this ester exhibits an A,B,E phase sequence, with the B phase being of the hexatic type. The synthesis, microscopic textures, and miscibility studies are reported here. The results show that while the two types of B phase appear co-miscible by conventional optical methods, in fact X-ray diffraction studies show that a transition occurs between the two phases in certain binary mixtures. Thus, the hexatic B and crystal B modifications are thermodynamically distinct phases.