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

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.

Analysis of the Tilt Angle for a Binary Mixture of C7-70PDOB Liquid Crystal Close to the Smectic A–Smectic C* Transition

“…As the concentration increases in a binary mixture of liquid crystals, a first order smectic A-smectic C (AC) or AC * transition changes toward a second order one, as observed experimentally in some binary mixtures such as C7 + 70PDOB [1,2], C7 + 10.O.4 [3,4] and SCE9 + SCE10 [5]. This has been demonstrated using the mean field models with the biquadratic coupling (P 2 θ 2 ) [6,7] and P 2 θ 2 + Pθ (bilinear) coupling in our recent studies [8][9][10][11], in particular for the binary mixtures of C7 + 10.O.4 [8], SCE9 + SCE10 [9,10] and C7 + 70PDOB [11].…”

“…As shown in these figures, our fits are reasonably good with the observed data [1], which also show a first order transition (X = 0, pure C7) that changes toward a second order as the concentration increases above X = 15.0 through the tricritical concentration (X = 16.92). Since at the tricritical point (TCP) the first order line intersects with the second order lines, as we have studied in our recent work [11] for the AC * transition in a mixture of C7 + 70PDOB near the tricritical point, above the TCP the transition becomes second order which is seen clearly at X = 19.4 ( Figs. 1 and 2).…”

“…We have also used this model for binary mixtures of SCE9 + SCE10 [9,10], C7 + 10.O.4 [8] and C7 + 70PDOB [11] close to the AC * transition in our previous studies.…”

“…A tricritical point (TCP) exists in this binary mixture for its AC * transition. Very recently, we have also studied on the AC * transition near the TCP in this binary mixture [11]. Using the mean field models with the P 2 θ 2 and P 2 θ 2 + Pθ coupling in the free energy expansion, for various concentrations X (70PDOB) we calculate here the tilt angle θ as a function of temperature.…”

Calculation of the tilt angle and susceptibility as functions of temperature and the electric field close to the Sm A – Sm C* transition in C7

“…Under the electric field applied, in particular, the Sm A-Sm C (C * ) transition of a first order has also been studied previously as reported in the literature [1][2][3][4][5][6][7][8][9][10][11]. Recently, ferroelectricity in liquid crystals with the experimental studies has been reviewed [12] and more recent studies in liquid crystal research in general have been given [13] in the literature.…”