Determination of Orientational Order Parameters of Two Tri-Component Mixtures from Optical Birefringence and X-Ray Diffraction Measurements

Abstract

Two tri-component mixtures as base mixtures for vertically aligned mode LCD's were prepared. The eutectic compositions were theoretically estimated and experimentally verified from differential scanning calorimetry studies. A room temperature nematic mixture with fairly broad operating range emerged from each of the tri-component mixtures. The optical birefringence of these mixtures at the eutectic composition was measured as a function of temperature. X-ray diffraction measurements were done on these mixtures to obtain the orientational order parameters as a function of temperature. The order parameter values were also determined from birefringence measurements and the results were compared with mean field theory. Structural parameters like intermolecular distance and apparent molecular length have also been determined.

Dielectric Permittivity and Viscoelastic Measurements οf Two Tricomponent Mixtures Consisting οf Laterally Fluorinated Terphenyl Derivatives

“…As reported by us earlier [4], both the theoretical as well as the experimental eutectic points for the tricomponent mixtures has been compared (Table II) and are found to be in reasonably good agreement with each other.…”

“…The performance of liquid crystal materials in LCD's depends critically on the temperature dependence of the dielectric, optical, elastic constants and rotational viscosity of the materials to be used. In continuation of our earlier work on two tricomponent mixtures (ABC and ABD) as base mixtures for vertically aligned (VA) mode LCD's [13], where we had reported the orientational order parameters from optical birefringence and X-ray diraction measurements [4], in this paper, we report the results of the dielectric permittivity, bend elastic constant and rotational viscosity measurements on these mixtures at the eutectic composition throughout their entire mesomorphic range. Vertically aligned mode applications require liquid crystalline materials with negative dielectric anisotropy [5,6].…”

“…Two tricomponent systems, ABC and ABD comprising of laterally uorinated dielectrically negative terphenyl derivatives and one bicyclohexane component were studied [4]. The chemical structure and transition temperatures of the four pure compounds are shown in Table I. (714) …”

“…Results of our optical birefringence measurements were reported in our earlier publication [4]. Optical transmission method was used to determine temperature dependence of the birefringence values.…”

“…The temperature dependence of γ 1 is tted with the following expression using the values of the orientational order parameter, S, determined from X-ray diraction measurement [4]:…”