Electron beam irradiation-induced transformations in the electrical properties of 4’-octyl-4-cyanobiphenyl (8CB)

Abstract

Changes in the dielectric and thermodynamical properties of electron beam-irradiated 4′-octyl-4-cyanobiphenyl (8CB) were studied. Irradiation-induced changes in the phase transition temperature, dielectric anisotropy, relaxation frequency and activation energy of an observed non-collective relaxation mode corresponding to molecular rotation about the short axis were determined in both nematic and smectic A_d phases. In the nematic phase, dielectric anisotropy increased for a small dose but decreased for a relatively high dose, whereas the relaxation frequency increased due to the irradiation. The pure and irradiated samples were characterised by UV–visible spectroscopy, Fourier transform infrared spectroscopy, gas chromatography, gas chromatography coupled with mass spectroscopy and pulse radiolysis. The observed changes in the dielectric parameters are related to the detachment of the CN group from some of the 8CB molecules due to the electron beam irradiation.

Keywords:

• electron beam irradiation
• dielectric parameters
• relaxation frequency
• UV-visible
• Fourier transform infrared spectroscopy

Acknowledgements

The work was financially supported under a DAE-BRNS research project. RV thanks DAE-BRNS for a fellowship under a research project. VKW also acknowledges the DAE-BRNS for the award of a Raja Ramanna Fellowship. R Dh especially thanks the University Grants Commission, New Delhi, for granting leave exclusively for research work under the National Research Award scheme.