Dielectric and thermodynamic studies of n-cyano-biphenyl (nCB) liquid crystals at microwave frequency

ABSTRACT

A study of dielectric and thermodynamic properties of three members 5CB, 6CB and 7CB from the family of n-cyano-biphenyl (nCB) liquid crystals is reported using the cavity perturbation technique at microwave frequency of 9.0 GHz. The observed shifts in the resonant frequency and widths of the resonance profile are used to analyse the dielectric permittivity and dielectric loss respectively. The loss tangents are calculated using relaxation times obtained from Debye’s single relaxation phenomenon. The temperature-dependent parameters such as free energy of activation, enthalpy and entropy are calculated for understanding all three thermotropic samples. For the dielectric investigation of very small amount of samples with high accuracy, the cavity perturbation technique suits well. The study provides interesting and neoteric results as comparison between various dielectric and thermodynamic parameters for nCB liquid crystals is not reported earlier at the given frequency.

KEYWORDS:

• Liquid crystals
• microwaves
• cavity perturbation
• dielectric relaxation
• phase transition

Acknowledgments

The authors are grateful to Late Prof. G. K. Johri for motivation and inspiration. The author (MJ) is full of gratitude to Late Prof. J. A. Roberts (USA) for measurements provided.

Disclosure statement

No potential conflict of interest was reported by the authors.