Importance of Steric Effects in the Isotropic Phase of Nematogenic Compounds

Abstract

The dielectric spectra of some mesomorphic substances in their isotropic phase are reported. The measurements are carried out from the radio frequencies up to the far infrared region. We have investigated several substances such as azoxybenzenes, cyanophenylcyclohexanes, azomethines, tolanes and biphenyls. Two special cases appear with the last two series where the dipole moment is directed either perpendicular or parallel to the long molecular axis respectively. The dielectric spectra show different absorption connected with rotational movements around or perpendicular to the long axis. The influence of the molecular surrounding on the dielectric properties is also studied by investigating the influence of dilution. The results have been discussed by using a computer simulation of molecular dynamics of fluid systems containing ellipsoidal particles which interact pair-wisely, assuming the interactions to be governed mainly by steric effects.