The dielectric behaviour of the nematic 5-n-hexyl-2-[4-n-alkyloxyphenyl]-pyrimidines

The dielectric constant and the dielectric loss of the 5-n-hexyl-2-[4-n-hexyloxyphenyl]-pyrimidine and the 5-n-hexyl-2-[4-n-nonyloxyphenyl]-pyrimidine were measured in the nematic and the isotropic region in a frequency range from 0.1 to 10 MHz. The dielectric anisotropy of both substances is found to be positive at frequencies below and negative at frequencies above the relaxation region. The temperature dependence of the isotropy frequency (Δϵ′  0) and the activation energies for the alignment of the dipoles in the electric field are calculated from the temperature dependence of the relaxation times.