Thermodynamic and dielectric studies of liquid crystalline compound (S)-(+)-4-(1-methylheptyloxycarbonyl)phenyl 4′-(6-octanoyloxyhex-1-oxy)biphenyl-4-carboxylate

Abstract

Dielectric spectroscopy of a newly synthesized antiferroelectric material (S)-(+)-4-(1-methylheptyloxycarbonyl)phenyl 4′-(6-octanoyloxyhex-1-oxy)biphenyl-4-carboxylate has been carried out over a frequency range 0.1 Hz to 35 MHz for a planar anchoring geometry of sample molecules. Material possesses paraelectric SmA* and ferroelectric SmC* phases along with antiferroelectric Sm phase. Generalized Havriliak–Negami equation has been applied to analyze the acquired dielectric data and consequently various dielectric parameters have been determined. SmC* phase shows two relaxation modes separated by about two decades of the frequency. The mode lying at the higher side of the frequency spectrum relates with Goldstone mode. Low-frequency mode with higher dielectric strength as compared to that of the Goldstone mode apparently seems due to the domain formation in the SmC* phase. SmA* phase shows single relaxation mechanism related with the soft mode. Two weak modes of dielectric relaxation have been detected in the Sm phase and these are related with the antiferroelectric ordering of the molecules in the phase.

Keywords:

• antiferroelectric liquid crystal
• dielectric spectroscopy
• relaxation
• soft and Goldstone modes
• DSC thermogram

Acknowledgements

Authors thank University Grants Commission (UGC), New Delhi for financial assistance under a major research project. S. Singh thanks UGC especially for a fellowship under the project. We wish to thank Dr M. Massey (Principal) and Dr L.C.T. Eusebius (Bursar), for their great help and encouragement for developing infrastructure facilities at ECC centre.