Characterization of Two Members of the N-(p-n-alkoxy benzylidene)-p-n-alkyl anilines (nO.m) Series Using Complementary Experimental Techniques

Abstract

In this study, we present a detailed investigation of the phase behavior of two homologues, namely 5O.12 and 5O.14, belonging to the series N-(p-n-alkoxy benzylidene)-p-n alkyl anilines (nO.m). A combination of high-resolution experimental techniques, including optical transmission, static dielectric permittivity, and modulated differential scanning calorimetry (MDSC), was employed to probe the isotropic–nematic (I–N), nematic–smectic A (N– SmA), and smectic A–smectic B (SmA–SmB) phase transitions. Temperature-dependent birefringence measurements indicate a progressive enhancement of orientational and bondorientational ordering upon cooling. Dielectric studies reveal negative dielectric anisotropy, attributed to the lateral dipole moment associated with the −C(H) = N− linkage within the molecular core. Calorimetric investigations, including heat-capacity anomalies and latentheat evaluation, confirm the first-order character of all observed transitions. Furthermore, critical analysis based on renormalization-group (RG) scaling expressions yields critical exponent values (α) characteristic of weakly first-order behavior. The results highlight the significant role of terminal alkyl chain length in modulating mesomorphic properties and provide deeper insight into the molecular ordering processes governing higher-order smectic phase transitions.