Temperature Dependence of the Tilt Angle for the Smectic A-Smectic Transition in a Mixture of C7-70PDOB Ferroelectric Liquid Crystals near the Tricritical Point

Mustafa Kurt,Hamit Yurtseven

doi:10.1155/2012/201972

Abstract

The temperature dependence of the tilt angle is studied in the smectic phase near the smectic A-smectic tricritical point for a mixture of 70PD0B in the ferroelectric liquid crystal C7 (). The mean-field models with the biquadratic ( is the spontaneous polarization) and (bilinear) coupling terms in the free energy expansion are used to analyze the experimental data for the tilt angle in this binary mixture. From our analysis, the coefficients given in the free energy expansion of the mean-field models are determined. Our results show that the mean-field theory explains adequately the observed behaviour of the C7-70PD0B mixture near the tricritical point.

Highlights

Smectic transitions in ferroelectric liquid crystals have been the subject of various experimental and theoretical studies
We focus on the temperature dependence of the tilt angle for a mixture of C7-70PDOB ferroelectric liquid crystal close to the tricritical point (TCP)
We have fitted to the experimental data [9] the expression for the tilt angle as a function of temperature, which we derive from the mean-field models with the P2θ2 and Pθ + P2θ2 couplings for the AC∗ transition close to the TCP

Summary

Introduction

Smectic transitions in ferroelectric liquid crystals have been the subject of various experimental and theoretical studies. We have studied the dielectric constant as a function of temperature for the AC∗ transition in 4-(3-methyl-2-chlorobutanoyloxy)4 -heptyloxybiphenly (A7) [21] and we have calculated a generalized smectic-hexatic phase diagram in various mixtures of liquids crystals [22]. We have used our mean-field model with the quadratic couplings Ψ2θ2 (Ψ is the orientational order parameter and θ is the tilt angle) for the smectichexatic phase transitions in various mixtures of liquid crystals in our recent study [22]. In order to get good fits, our θ versus T expression is favorable On this basis, we have fitted to the experimental data [9] the expression for the tilt angle as a function of temperature, which we derive from the mean-field models with the P2θ2 and Pθ + P2θ2 couplings for the AC∗ transition close to the TCP.

Theory

Calculations and Results

Discussion

Conclusions