NEMATIC PHENYL BENZOATES IN ELECTRIC-FIELDS .1. STATIC AND DYNAMIC PROPERTIES OF DIELECTRIC PERMITTIVITY

For n equals 2 the dielectric anisotropy DELTA epsilon equals epsilon // minus epsilon (perpendicular) is found to be positive. For n equals 1, however, the sign depends on the para substituents. In particular, replacement of an alkyl group by an alkoxy group shifts DELTA epsilon towards negative values. The frequency dependence of epsilon // shows a relaxation at relatively low frequencies (kHz range), while epsilon (perpendicular) 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 DELTA epsilon the relaxation leads to a change of sign of DELTA epsilon which is of interest for the study of electrohydrodynamic instabilities.