Optical and Thermodynamic Properties of Mixtures of Pleochroic Dye with Some Alkyl-Cyanobiphenyl Liquid Crystals

Abstract

The temperature dependence of the refractive indices, guest and host order parameters as well as the melting and clearing points for the binary mixtures of the pleochroic dye in some members of the homologous series of the alkyl-cyanobiphenyl have been measured. Odd-even effect in some thermo- dynamic properties of the mixtures investigated was observed. A good compatibility between the shift in the nematic-isotropic transition temperature after dye addition and activity coefficient ratio on the one hand and the mutual connection between guest and host order parameter in the vicinity of the clearing point on the other have been found. The experimental results were compared in some details with calculations done on the basis of the Maier-Saupe theory for binary mixtures. It was demonstrated a good agreement between experiment and theory taking into account the flexibility of the end-chain of the host.

Key Words:

• guest-host system
• alkyl-cyanobiphenyl
• refractive index
• order parameter
• phase transition temperature