Effect of Alkyl Chains Length on Ferroelectric Properties of Km/n and KLLm/n Homologous Series

Abstract

In this work, a phenomenological thermodynamic model is used to describe the temperature variations of spontaneous polarization P 0 , tilt angle θ 0 , and helical pitch p of Sm C * phase near Sm A-Sm C * phase transition in two homologous series, Km/n and KLLm/n, of ferroelectric mesogens. The free-energy density of the system is written in terms of tensor orientational order parameter Q ij , scalar smectic order parameter ψ, vector polarization order parameter P, and the resulting couplings between these order parameters. The tilt vector ξ is not considered an independent order parameter, as that Q ij governs ξ . Adopting usual method, we evaluate the relative contribution of each individual term of the expansion series and the values of P 0 , θ 0 and p as a function of temperature for the eleven ferroic mesogens, and found that the theoretical results agree very well with the experimental data of all the mesogens.