Frequency shift in smectic multiple relaxations and the effect of a flexible end chain

Abstract

The low frequency (LF) dielectric constant was studied as a function of temperature in the Schiff 's base liquid crystalline compounds of N (p - n -alkoxybenzylidene)- p - n -alkylanilines with the applied field parallel to the director to determine the phase transition temperatures and the underlying dipolar association. The low frequency (1 kHz to 10 MHz) complex dielectric spectrum systematically studied in the smectic polymorphs of these compounds implied multiple relaxations. The rotational degrees of freedom were found to be squeezed with the decrease of temperature as the low temperature smectic phases were approached. The ColeDavidson method was used to differentiate the fast dynamics of the rigid core-associated dipole from the slow component of the flexible end chain. A comparative study of the orientational dynamics of the rigid core dipole (type I) was carried out by designing a normalized scale in smectic phases. Arrehenius dependence was used in the estimation of smectic relaxation frequency at a common normalized smectic temperature scale point. The results imply the downward shift of frequency with increase in length of the flexible end chain. The distinct loss of rotational degrees of freedom of the rigid core dipole with increasing chain length suggests its solute particle behaviour in the solvent concentration.