The effect of non-mesogenic biphenyl impurity on the orientational order parameter of 4-cyano-4′-n-octyl-biphenyl (8CB)

The role of non-mesogenic impurities on a mesogen and the consequent alteration of mesogenic properties have always been of great interest in the tailoring of mesogenic behaviour. In the present work the effect of rigid, non-polar, nonmesogenic solute ‘biphenyl’ on the optical properties of the mesogen 4-cyano-4′-n-octyl-biphenyl (8CB) has been reported. The phase transitions and thermal variations of the refractive index, polarisability and order parameter ⟨P2⟩ of the 8CB–biphenyl systems of various concentrations have been investigated using a He–Ne laser beam. The results have been compared with ⟨P2⟩ of pure 8CB. It has been observed that biphenyl lowers both smecticA–nematic and nematic–isotropic transition temperatures by an amount that depends on impurity concentration.