Comparison of the dielectric relaxation data for the isotropic and nematicphases of three homologous series: nCb, nOCB and nPCH, (n=5 divided by 8)

Results of dielectric studies of three homologous series: n-alkyl-cyanobiph enyls - nCB, n-alkyloxy-cyanobiphenyls - nOCB, and trans-4-(4'-n-alkyl-cycl ohexyl)-cyanobenzene - nPCH, with n from 5 to 8, are presented. The paramet ers characterizing the rotational motions of the molecules around their sho rt axes in the nematic and isotropic phases were derived (dielectric increm ents, relaxation times, activation enthalpies, retardation factors, nematic potentials, order parameters). Comparative analyses of the parameters in r espect to mr length, of the terminal groups and the structures of the molec ular cores are given.