GROWTH OF SMECTIC-B (CRYSTAL) AND PHASE-TRANSITIONS IN LIQUID-CRYSTALLINE PBNA (N=4, 5, AND 6) COMPOUNDS

Thermal microscopy, calorimetric (DSC) and dilatometric investigations are reported in three liquid-crystalline compounds of n(4-n-phenylylb enzylidene) 4-n-alkylaniline series viz., PBnA for n = 4, 5, and 6. Th ey exhibit nematic, smectic B (cryst) and smectic E (monotropic) polym orphism Effective role of terminal phenyl end chain is discussed for t he occurrence of 3D-ordered smectic B and smectic E phases. Density ju mps and associated volume expansion coefficient anomaly infer first or der nature of isotropic to nematic (IN) and nematic to smectic B (NB) transitions. Exponential growth of three-dimensional hexagonal positio nal correlations estimated in the vicinity of nematic to smectic B tra nsition through the beta exponent infers the Van der Waals type of mol ecular interactions. Pressure dependence of transition temperatures ar e estimated, IN and NE transitions and thermal stability are discussed .