Dielectric Behaviour of 1-(4-Isothiocyanatophenyl)-2-(4-hexyl- bicyclo[2,2,2]octane-1)ethane in Nematic and Isotropic Phases

Abstract

Static and dynamic investigations of the dielectric properties of the liquid crystal l-(4-isothiocyanatophenyl)-2-(4-hexyl-bicyclo[2,2,2]octane-l)ethane in the nematic and isotropic phases have been carried out in the frequency region from 1 kHz to 1 GHz. Two relaxation processes, described by the Debye functions, have been observed not only in the isotropic but also in the nematic phase, when the measurements of the electric permittivity vs. frequency have been made parallel to the orientation axis of liquid crystal. These processes are related to the rotation of the permanent dipole moment around two main molecular axes. The height of the potential barrier which hinders the rotation of the liquid crystal molecule around the short axis in the ordered nematic phase and the order parameter of the liquid crystal investigated have been estimated on the basis of the relaxation time values in the nematic and isotropic phases.

Nematic Potential and Order Parameter Determined from Dielectric Measurements

“…It has been shown that such a theoretical calculation of S agrees fairly well with experimental results obtained by various methods at ambient pressure as well as at higher pressures [9,10]. In this work we apply such calculations for the analysis of recently obtained high-pressure dielectric data.…”

Molecular Dynamics of 4-(trans-4'-n-Heptylcyclohexyl)- Isothiocyanatobenzene Studied with Dielectric Relaxation Spectroscopy

“…The nematic potential causes the long-range orientational order and hinders the rotation of the molecules around the short axis, so the corresponding relaxation time is significantly longer than that in the isotropic phase. This fact allows one to determine the height of the nematic potential barrier and thus the orientational order parameter from the dielectric data [4][5][6][7][8].…”