Dielectric anisotropy studies in nematic mixtures

Measurements of dielectric permittivity components epsilon(//) and epsilon( perpendicular to) have been made on five nematic mixtures: ZLI2687, ZLI2788 -000/100 and ZLI2447-000/100, at 2 kHz in their nematic,phases. All the nem atogens exhibit positive dielectric anisotropy Delta epsilon (epsilon(//) - epsilon(perpendicular to)) and mean permittivity epsilon(epsilon(//)+2 eps ilon(perpendicular to)/3) lower temperatures the S/T dependence of orientat ion polarization predominates over the induced polarization, so that Delta epsilon exhibit's a constant value for ZLI2687. Near the nematic isotropic transition this mesogen exhibited two phase coexistence where Delta epsilon attained a small constant value. In ZLI 2788-000/100 mixtures which contai n additional ester components compared with ZLI 2687, the dielectric permit tivity components become larger, which is probably from a greater contribut ion to the dipole moment induced by the ester component. An additional comp onent PDX in ZLI 2447-000/100 compared with ZLI 2788-000/100, however, decr eases slightly the values of Delta epsilon. Further, the dielectric anisotr opy Delta epsilon for ZLI 2788-000 is larger than for ZLI 2788-100 and also for ZLI 2447-000 is larger than for ZLI 2447-100, which perhaps reflects t he increased molecular weight. Surprisingly in ZLI 2447-100, near the nemat ic-isotropic transition, the value of epsilon(//) falls abruptly, so that D elta epsilon assumes a small negative value. This may be due to pre-transit ional