PRETRANSITIONAL EFFECTS AT THE ISOTROPIC MESOMORPHIC PHASE-TRANSITIONS IN THE TBAA SERIES

Thermal microscopy (TM), differential scanning calorimetry (DSC) and d ilatometric rho(t) experiments were carried out to characterize the ph ases and to study the nature of mesomorphic transitions in two higher homologues of terephthalylidene-bis-p-n-alkylanilines, TBnAs, namely t erephthalylidene-bis-p-n-tetradecylaniline, TB14A and terephthalyliden e-bis-p-hexadecylaniline, TB16A. Results infer the first order nature of the isotropic-smectic C (I-S-C) and smectic C-smectic I(S-C-S-I) tr ansitions, while the smectic I-smectic F (S-I-S-F) transition is found to be second order. Pretransitional effects are estimated through alp ha(eff) in the vicinity of mesomorphic fluctuation dominated non-linea r regions (FDNLR), of the isotropic to mesomorphic transitions in TBnA homologous compounds and the relative strength of growth of FDNLR is discussed at the SIN, S(I)A(S), and SISC phase transitions.