Nematic Phenyl Benzoates in Electric Fields: I. Static and Dynamic Properties of the Dielectric Permittivity

A discussion is given of the dielectric properties of some nematic phenyl benzoates with the structure For n = 2 the dielectric anisotropy Δ∊=∊‖– ∊⊥ is found to be positive. For n = 1, however, the sign depends on the para substituents In particular, replacement of an alkyl group by an alkoxy group shifts Δ∊ towards negative values. The frequency dependence of ∊‖ shows a relaxation at relatively low frequencies (kliz range), while ∊⊥ remains constant. The activation energy for this relaxation is 0.4 till 0.5 eV for all the compounds studied. In case of a positive static Δ∊ the relaxation leads to a change of sign of Δ∊ which is of interest for the study of electrohydrodynamic instabilities.