The Dielectric and Optical Properties of the Homologous Series of Cyano-Alkyl-Biphenyl Liquid Crystals

The electric permittivities, refractive indices and densities of the homologous series of alkyl-cyano-biphenyls (C n H 2n+1 .φ.φ.CN) have been measured as a function of temperature in the nematic phases for n = 5 to 9, and in the smectic phases for n = 8 and 9. The results have been analysed in terms of the Maier and Meier theory to yield values for the molecular dipole moments and polarizabilities. Kerr effect measurements on dilute solutions of 44′-n-pentyl-cyano-biphenyl at different temperatures are reported, and in conjunction with similar dielectric and optical measurements have provided results for the free molecule dipole moment and polarizabilites; values for the higher homologues are predicted using a bond additivity model. Bordewijk's theory is applied to the permittivity measurements, and using appropriate molecular parameters, dipole-dipole correlation factors are calculated.