The Study of the Guest Effect on the Nematic Phase Stabilization

Abstract

The effect of azo-dye on some optical and thermodynamical properties of the liquid crystal 5CB are examined. The relation between molecular geometry of the guest, guest and host order parameters and nematic-isotropic transition temperature of the azo-dye/liquid crystal mixtures is determined. The experimental results are compared in some detail with calculations done on the basis of the molecular mean-field theory and predictions of the lattice models as well. It has been found that good agreement between experiment and theory can be obtained taking into account not only the molecular sizes of the solute and the guest-host interaction, but also the concentration dependence of the dye order parameter and the flexibility of the end-chain of the liquid crystal molecules.