Dielectric spectroscopy of unsymmetrical liquid crystal dimers showing wide temperature range TGBA and TGBC* phases

Abstract

The electrical properties of frustrated twist grain boundary (TGB) phase are a matter of curiosity. Some studies have indicated the existence of soft and Goldstone modes in TGBA and TGBC* phases respectively. However, the experimental results are still not very conclusive. In the present work, we report dielectric studies of wide temperature range TGBA and TGBC* phases of an optically active dimeric compound 4‐n‐decyloxy‐4′‐(cholesteryloxycarbonyl‐1‐butyloxy) chalcone in the frequency range of 1 Hz to 35 MHz for the planar and homeotropic anchoring of the molecules. Two different relaxation processes have been detected for the planar anchoring of molecules in the TGBA and TGBC^* phases. The soft mode like behaviour is obtained due to tilt fluctuation of molecules in the megahertz region for both TGBA and TGBC* phases. Goldstone mode like behaviour due to phase fluctuation of molecules has been detected for the TGBC* phase in the low frequency region (∼200–300 Hz). Activation energies for DC conductivity have also been determined for various phases of the material.

Keywords:

• TGB phases
• dielectric permittivity and anisotropy
• dielectric strength
• relaxation frequency
• ionic conductivity.

Acknowledgements

We thank the Department of Science of Technology (DST), New Delhi for financial support under a research project. ASP thanks the DST for fellowship under the project. RD thanks the University Grants Commission, New Delhi for leave from teaching lead under the National Research Award scheme. We are grateful to Professor I.M.L. Das, In‐charge Impedance Spectroscopy Laboratory, and Professor Pradip Kumar (Head), Physics Department, Allahabad University for providing low frequency dielectric measurement facilities.