Dielectric properties of 4′-n-alkyl-4-cyanobiphenyls in their nematic phases

Abstract

The principal dielectric constants of the pentyl to octyl derivatives of 4′-n-alkyl-4-cyanobiphenyl have been measured as functions of temperature in their nematic and isotropic phases. All the compounds exhibit a strong positive dielectric anisotropy due to the presence of a large dipole moment along the major molecular axis. The principal dielectric constantse ‖ ande ⊥ as well as the anisotropy Δe decrease with increasing alkyl chain length. The experimental value of $$\bar \in = \frac{1}{3}$$ (e‖+2e⊥) decreases with decreasing temperature, and is throughout less than the extrapolated isotropic value, in conformity with the model of antiferroelectric short range order proposed by Madhusudana and Chandrasekhar.