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

Abstract

Two tricomponent room temperature nematic eutectic mixtures ABC and ABD with laterally uorinated constituents A and B were prepared as base mixtures for vertically aligned mode LCD's. The physical properties of these mixtures viz. birefringence, dielectric anisotropy, bend elastic constant, relaxation time and rotational viscosities were determined in order to compare with the optimum values required to achieve the target specications of VA mode materials. The dielectric anisotropy, ∆ε, and optical birefringence, ∆n, of these mixtures were found to be in the range of (1.3 to 1.4) and (0.13 and 0.14), respectively, at around 20• C. The gure of merit for the ABD mixture has been found to be higher than that of ABC mixture throughout the entire temperature range. The pretilt angle eect in the physical parameters has also been studied. At T = 20• C, the response time decreases to 25% and 35% for mixture ABC for 2• and 5• pretilt respectively in comparison to zero pretilt. On the other hand, at the same temperature for the ABD mixture these values are reduced by 16% and 35%, respectively.