Dielectric Relaxation Study of Two Different Mesogenic Cinnamates with a Substituted Ethyl Terminal Chain

Abstract

Dielectric studies of liquid crystals are important as they provide information about their molecular structure, intermolecular interaction, and molecular dynamics. The dielectric relaxation has been investigated for two different mesogenic cinnamates with a substituted ethyl terminal chain, β-methoxyethyl [4-(4′-n-octyloxycinnamoyloxy) benzoates (ME8OCB), and β-chloroethyl [4-(4′-n-octyloxycinnamoyloxy) benzoates (CE8OCB). The ME8OCB exhibits an enantiotropic smectic A (SmA) and a nematic mesophase whereas CE8OCB exhibits only an enantiotropic SmA mesophase. The real and imaginary parts of permittivity and dielectric anisotropy have been measured using an impedance/gain phase analyzer in the frequency range 100–10 MHz. The measurements have been carried out in the temperature range 80°C–136°C. The measurement in the smectic phase indicates dielectric dispersion. The relaxation time and activation energies have also been determined. The result suggests that there is a molecular rotation about molecular axis. The dielectric anisotropy falls with a rise in temperature but mean dielectric permittivity increases with a rise in temperature.