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 constants ε11 and εL as well as the anisotropy ∆ε decrease with increasing alkyl chain length. The experimental value of έ = ⅓( ε11+ 2εL) decreases with decreasing temperature, and is throughout less than the extrapolated isotropic value, in conformity with the model of antiferro- electric short range order propored by Madhusudana and Chandrasekhar.