Change of Molecular Polarizability Density and Nature of the Smectic A – Crystal B Phase Transition of Liquid Crystal 2O.2C

Abstract
Components of the molecular polarizability density (G_j = γ_j/v) for light waves polarized along (j = ||) and across (j =

) the optical axis of uniaxial liquid crystal are related to the components of polarizability (γ_j) and the volume per molecule in the medium (v). In this work, the dependences of G_γ (components G_j, mean value G_m and anisotropy G_α) on temperature and light wavelength (λ) were determined for smectic A and crystal В phases of liquid crystalline ethyl-p-(4-etoxybenzylideneamino)cinnamate. The temperature dependences of the effective wavelengths (λ_γ) for electronic transitions which are responsible for dispersion G_γ(λ) in the visible range were obtained in both phases. The relation between the values of λ_γ and the characteristics of real electronic transitions (wavelengths, oscillator strengths and polarizations) and the orientational order parameter (S) of molecules was established. Using the values G_γ and λ_γ it was revealed that the smectic A – crystal B phase transition is accompanied by very small change of S, decrease in the anisotropy of molecular polarizability and change of the polarization of electronic transitions.

Keywords: polarizability of mesogenic molecules, phase transitions in liquid crystals, intermolecular interactions