Temperature dependence of polarizability, order parameters and dielectric properties of a nematic liquid crystals

The optical and dielectric parameters of a nematic liquid crystals material (E-24) having high optical birefringence (>0.2) was investigated. Principal polarizabilities ( α o , α e ) and polarizability anisotropy ( α o – α e ) were calculated using Vuks’, Neugebauer’s and Maier & Saupe’s approaches. Experimental data of extraordinary refractive index (nₑ), ordinary refractive index (nₒ) and density (ρ) were used to calculate these parameters. The present study is based on three approaches: the isotropic field model suggested by Vuks, anisotropic internal field adopted by Neugebauer and isotropic internal field model suggested by Maier & Saupe, in which an additional parameter, the internal field factor was introduced. The order parameter (S) of the studied material was obtained using six approaches. The values of S were found to be in between 0.6 and 0.7 by all methods at room temperature. The dielectric anisotropy ( ∆ ∈ ′ = ∈ ‖ ′ − ∈ ⊥ ′ ) and average dielectric permittivity < ∈ ′ > = ∈ ‖ ′ + 2 ∈ ⊥ ′ 3 , have been obtained by using parallel ( ∈ ‖ ′ ) and perpendicular ( ∈ ⊥ ′ ) components of dielectric permittivities. The molecular dipole moment (μ) and angle of inclination (β) of the dipole axis were obtained using the dielectric parameters. The dipole moment μ vary between 2.83D (at 293 K) and 2.99D (at 326 K). The angle of inclination (β) also changed from 31 0 (293 K) to 54 0 (326 K) in the nematic phase of the studied material. • The optical and dielectric properties of a nematic liquid crystals were investigated. • Refractive indices, density and dielectric data were measured experimentally. • Principal polarizabilities ( α o , α e ) were calculated theoretically by using Vuks’, Neugebauer’s, Maier and Saupe’s approaches. • The order parameters (S) for the studied material have been obtained by using six theoretical approach. • Molecular dipole moment (μ) and the angle of inclination (β) of the dipole axis with the director ( n ˆ ) have been calculated.