Comparative Studies of the Degree of Order of the Guest and Host Molecules in 4-Cyano-4′-n−Heptyl-p−Phenylcyclohexane (PCH7) Mixtures

Abstract

The dielectric relaxation parameters and the refractive indices for the nematogen 4-cyano-4′-n−heptyl-p−phenylcyclohexane (PCH7) and for the azo dye-PCH7 mixtures are reported. The host order parameter, <P ₂> _H both from the temperature dependence of the refractive indices and from the dielectric relaxation time is estimated. Additionally, the guest order parameter, <P ₂> _G from the absorption dichroic ratio is determined. It is found, that the order parameter obtained from the optical study is changed differently than that derived from the dielectric relaxation measurements when the dyes with the polar—NO₂ end group are added. A comparison of <P ₂> _H for Pure PCH7 with that for the nematogen 4-cyano-4′-n−pentyl-p−biphenyl (5CB) or for the azo dye-liquid crystal mixtures shows that the short range order in the nematic host depends on the degree of the aggregation of the liquid crystal molecules in the samples investigated.

Key Words:

• guest-host mixture
• electric permittivity
• refractive index
• order parameter