Dielectric study of three homologous Schiff base ferroelectric liquid crystals with the variations of temperature and frequency

Abstract

In this investigation, the dielectric behaviors of three ferroelectric liquid crystals (FLCs) belonging to a homologous series have been revealed in the frequency range of 10 Hz–10 MHz. FLCs used in this study are three-ring calamitic LCs, namely ([Formula: see text])-4-(((4-(octan-2-yloxy)phenyl)imino)methyl)phenyl 4-([Formula: see text]-octyloxy)benzoate, ([Formula: see text])-4-(((4-(octan-2-yloxy)phenyl)imino)methyl)phenyl 4-([Formula: see text]-decyloxy)benzoate and ([Formula: see text])-4-(((4-(octan-2-yloxy)phenyl)imino)methyl)phenyl 4-([Formula: see text]-undecyloxy)benzoate. The polarizing optical microscopic and differential scanning calorimetric results confirm that these compounds, synthesized as per the known synthetic steps, show not only a ferroelectrically switchable chiral smectic C (SmC*) phase over a wide thermal range, but also other mesophases such as blue phase-I/II (BP-I/II), chiral nematic (N*) and unknown smectic (SmX) phases. Several essential dielectric parameters of the FLC phase have been measured at different temperatures. The relative permittivity has been measured with the variations of temperature and frequency. Besides, the dielectric loss and tan [Formula: see text] have been measured. Different dielectric relaxations have been calculated and explained at the molecular level. The systematic measurements revealed a strong anomaly, and crossover of relative permittivity values for the FLCs has been determined at selective frequencies between 1 kHz and 20 kHz. Strong dielectric anomaly/fall for the response function infers the involvement of collective response of dipolar assembly confined to ferroelectric Weiss domains.