Relaxation Phenomena in the Nematic, Nismatic Reentrant and Smectic A Phases Studied by Dielectrhic Spectroscopy

Abstract

Dielectric properties and relaxation process of hinary mixture (MIX I) and quaternary mixture (MIX II), both composed of 4-alkylphenykarbonyloxy-4-eganophenyls and -4′-cyanobiphcnpls, have been studied by dielectric spectroscopy in the frequency rang from 5 fat to 10 GHz. Dielectric measurements have been done for two principal alignments of the N, SmA_d and N_R phases. In the caw of MIX II the parallel component of dielectric permittivity shows a pronounced decrease in the Sm A_d phase due to dipole-dipole correction. This anomaly is much weaker for MIX I. Lon frequency spectra for both mixtures consist of two well separated al, absorption peak. connected, respectively, with biphenyl and triphenyl ring entities. By fitting a sun of two Cole-COIF functions it was possible to compute dielectric parameters of the relaxation process observed. In both cases the relaxation times exhibit Arrhenius type behavior with activation energy higher in the N_R than and N phases. At high frequencies (from 10MMz to 10GHz) a broad spectrum, originating from a number of relaxation processes, have been observed.