Dielectric properties of a highly polar liquid crystalline material showing various types of layered structures

ABSTRACT

Liquid crystal compound N-(4-n-pentyloxybenzalidene) 4′-n-pentylaniline is very interesting because of its rich phase variant, i.e. nematic, smectic A, smectic C, smectic F and smectic G phases. In the present work, temperature- and frequency-dependent dielectric studies on this compound in the homeotropic and planar orientation of molecules have been carried out in the frequency range of 1 Hz–10 MHz. The compound shows negative dielectric anisotropy (i.e. Δε < 0). Dielectric studies have shown three relaxation modes of different origin in various phases of the material. Relaxation frequencies of the observed modes follow Arrhenius behaviour. The relaxation due to interfacial polarisation, i.e. Maxwell–Wagner–Sillars effect has been observed in the nematic and isotropic phases. A relaxation mode due to the fluctuation of molecular tilt resembling the soft mode has been detected in the smectic A phase with pre- and post-transitional effects. Another mode due to the fluctuation of molecules about their short axes has been detected in the nematic and smectic A, C, F and G phases. Activation energies and ionic conductivity of these phases have also been determined.

GRAPHICAL ABSTRACT

KEYWORDS:

• Permittivity and loss
• dielectric relaxation modes
• conductivity
• nematic and smectic phases

Acknowledgement

One of the author (RG) wishes to thank the Centre of Material Sciences, University of Allahabad, Allahabad and Department of Physics, NERIST, Nirjuli, for providing facilities.

Disclosure statement

No potential conflict of interest was reported by the authors.