Weak forces for the growth of smectic-F liquid crystal

N(p-n-dodecyloxybenzylidene)p-n-alkylanilines, viz., 12O.m compounds of nO.m series, for m = 4, 5, 6, 8, 10, 12, 14 and 16 are synthesized and characterized by Polarized Thermal Microscopy (TM) and Differential Scanning Calorimetry (DSC). These compounds are found to exhibit 2D Bond-Orientationally (BO) ordered smectic-F liquid crystal phase with shift distortion along with orthogonal smectic-A, -B(cryst) phases. The intermediate members of the compounds of 12O.m series (m<10) are found to exhibit orthogonal smectic phases along with the tilted phases, while the higher homologues (m>10) show the tilted bond-orientational smectic phases only. The miscibility studies for the confirmation of smectic-F phase through binary (12O.12+10O.14) phase diagram, suggests the possibility for the occurrence of smectic-F phase down towards ambient temperatures. The smectic-G phase melting temperature. T_FG is found to depress at lower and higher concentrations (x), while smectic-F phase clearing temperature T_IF remains constant with the concentration. The thermal span of smectic-F phase is found to depend on the chemical potential (represented by the mole fraction x) in the (T, x) phase diagram. The cubic fit in the vicinity of lower/higher concentrations, qualitatively infers the weak nature of Van der Walls' molecular forces for the growth of pseudo-hexagonal packed quasi-2-D BO ordered S_F liquid crystal with a poor registry of positional correlations.