Phase transition and pre transitional studies across isotropic - Smectic-F and G phases in N-(P-n-alkoxybenzylidene)p-n-tetradecyl anilines, (nO.14): A dilatometry study

The higher homologues of N-(p-n-alkoxy benzylidene) p-n-alkylanilines, (nO.m) viz., N-(p-n-alkoxybenzylidene)p-n-tetradecylaniline, nO.14 compounds with n=10 to 16 exhibit a direct smectic-F phase from cooling the isotropic liquid, while the compound with n=18 shows a direct smectic-G phase from isotropic liquid. Density studies are carried out across isotropic-smectic-F, isotropic-smectic-G and smectic-F-smectic-G phases. The density jumps and thermal expansion coefficient maxima across these phases infer a first order IF or FG transition. The strength of pre-transitional effects studied through α _effacross isotropic to nematic (IN), isotropic to smectic-A (IA) and isotropic to smectic-C (IC) phases. The α _eff and the fluction dominated non linear region (FDNLR) values for T>T _c obtained for these compounds underlines the increase of orientational disorder extended deep into the isotropic liquid for the formation of either smectic-F or smectic-G phase than in the case of the lower homologues exhibiting IN and IA phase transitions.