Dilatometric studies across the isotropic to smectic-F transition

Thermal Microscopy (TM), Differential Scanning Calorimetry (DSC) and dilatometric studies were carried out to characterise the liquid crystalline phases and mesomorphic transitions exhibited by three higher homologues of N-(p-n-dodecyloxy benzylidene)p-n-alkyl anilines, viz., N-(p-n-dodecyloxy benzylidene)p-n-dodecyl aniline, (12O.12), N-(p-n-dodecyloxy benzylidene)p-n-tetradecyl aniline, (12O.14) and (N-(p-n-dodecyloxy benzylidene)p-n-hexadecyl aniline, (12O.16). The three compounds exhibit enantiotropic smectic-F and smectic-G liquid crystalline phases between the isotropic liquid and the solid crystal. The change in density across the phase transformations and the thermal expansion coefficient confirm the first order nature of the isotropic to smectic-F (I-SmF) and smectic-F to smectic-G (SmF-SmG) transitions. The dilatometric studies infer strong pre-transitional fluctuations in a relatively large thermal range. The pre-transitional effects are estimated by α_eff in the vicinity of the mesomorphic fluctuation-dominated non-linear region (FDNLR) of the I-SmF transition. The strength of non linear growth of density fluctuations is discussed in the wake of reports at the I-N, I-SmA and I-SmC transitions.