Study of the Dielectric Properties of 7PCH (4 -(trans -4 -Heptyl-Cyclohexyl)-benzonitrile)

Abstract

Abstract The results of dielectric studies of 7PCH (4-(trans-4-heptyl-cyclohexyl)-benzonitrile) in the nematic and isotropic phases are presented. The complex dielectric permittivity, ε*=ε' - i ε", was measured in the frequency range 1 kHz-5 GHz, with the use of an impedance analyzer and a time domain spectroscopy (TDS) set-up. The relaxation times: longitudinal tII, and transverse t^ in the nematic phase, and tis in the isotropic phase, were obtained. They served for calculation of the activation barriers for different molecular rotation processes occurring in both phases. Additionally, the retardation factors g II and g ^ were calculated. Two theoretical models (Meier-Saupe and Coffey et al.) were applied for tne calculation of the nematic potential q. A critical analysis of accessible literature data on the order parameter S is given. On that basis the relation q - SS is tested. The obtained values of the strength parameter S are lower for 7PCH than for 5PCH. Possible contribu­tions to the total energy barrier hindering the molecular rotation around the short axis in the nematic phase are considered.