Time Domain Reflectometry Studies on a Nematic Liquid Crystal

Abstract

The complex dielectric permittivity spectra of p-pentyl phenyl-p-propylbenzoate (PPPB) , of a nematic liquid crystal are obtained using Time Domain Reflectometry (TDR) method over a frequency range 10 MHz–10 GHz at various temperatures covering both nematic and isotropic phases. The relaxation behavior at different temperatures was studied through cole–cole arc. The dielectric behavior in nematic (N) phase could be described by the Cole–Davidson model, while isotropic (I) phase is found to obey to a large extent Debye model. Two relaxation times, τ1 and τ2, are obtained for N phase which are the characteristic of Cole–Davidson model. τ1 and τ2 are interpreted as corresponding to different degrees of freedom in different direction in liquid crystalline state. The fact that τ1 and τ2 obtained for the I phase are almost equal favors Debye model. The results are presented over a temperature range, and these results are discussed to understand the phase transition involved. The work included in this article is useful as it provides information about the macroscopic structure of the liquid crystals in general and PPPB in particular. The N phase is the least ordered of liquid crystalline phases, and hence the studies even on an unaligned samples give information that is very close to aligned ones as far as those properties which are due to overall effects like dielectric behavior.