Nematic Phenyl Benzoates in Electric Fields. II. Instabilities Around the Frequency of Dielectric lsotropy

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Abstract
The instabilities in AC fields are discussed for a planai layer of a nematic mixture of two phenyl benzoates. Due to a relaxation of ∊⊥ a reversal of the sign of the dielectric anisotropyΔ∊ occurs at the frequency f 0. Above f 0 (negativeΔ∊) there is a conduction regime with domains and dynamic scattering. This regime can be understood using an extension of the existing onedimensional model for electrohydrodynamic instabilities in which the dielectric losses of ∊⊥ are taken into account. At low frequencies (large positiveΔ∊) a Freedericks-transirion from a planar to a hometropic orientation occurs. In between is a region (small positiveΔ∊) where domains are observed at the threshold and disappear at higher voltages. For this region a two-dimensional model combining the two limiting cases is essential.