Optical and dielectric properties of the mesogen 4-cyano-4′-n–octyl biphenyl as a function of temperature

Abstract

The effect of temperature on certain optical and dielectric properties of one member, namely 4-cyano-4′-n–octyl biphenyl (8CB) of the mesogenic series 4-cyano-4′-n–alkyl biphenyl (nCB), is reported. The dependence of the ordinary and extraordinary components of polarisability, α_o and α_e, on temperature is studied using a He–Ne laser beam, and the variation of orientational order parameter with temperature in the entire mesogenic phase determined from the optical studies. The dependence of the effective molecular dipole moment, μ_eff, in the liquid-crystal phase, and the angle of inclination, β, of the dipole moment with the preferred direction have been investigated. An experimental estimate of the correlation factor ‘g’, which is indicative of the nature of the molecular association in the mesophase, has been obtained.

Keywords:

• Birefringence
• Order parameter
• Dipole moment
• Correlation factor

Keywords:

• PACS No: 61.30

Acknowledgements

The authors are thankful to Dr. C. D. Mukherjee of Saha Institute of Nuclear Physics, Kolkata, for supplying the material. Thanks are due to Prof. P. Nandy, Department of Physics, Jadavpur University, Kolkata, for the use of laboratory facility for texture studies. The authors thankfully acknowledge a research project grant from the University Grants Commission (U.G.C.), India. S.C. is thankful for the U.G.C. Research Associate fellowship under the above project.