Dielectric and electro-optic behaviour of two chiral compounds and their antiferroelectric mixtures

Abstract

Dielectric and electro-optic properties of two chiral compounds (MHPOBC analogues) and their three antiferroelectric mixtures have been studied. Mixtures of both compounds show SmA*, SmC*_α, SmC* and an induced antiferroelectric phase, which is not present for pure substances. All materials were studied using differential scanning calorimetry, frequency domain dielectric spectroscopy and the reversal currents method. Spontaneous polarisation of the mixtures is between 200 and 280 nC/cm²; in the antiferroelectric phase it depends linearly on temperature. Ferroelectric and antiferroelectric phase of mixtures display a mono-domain texture grown in a strong electric field upon slow cooling from the SmA* phase. In the SmC* a domain mode was observed under the bias field, while the antiferroelectric phase shows two characteristic dielectric relaxation processes that are weakly bias field dependent. The low frequency relaxation is not a single Debye-type process, and it also shows up without a bias field. The dielectric data will be discussed based on the Parry-Jones–Elston theory.

Keywords:

• ferroelectric liquid crystals
• induced antiferroelectric phase
• dielectric properties
• relaxation phenomena

Acknowledgements

The research was carried out with the equipment purchased thanks to the financial support of the European Regional Development Fund in the framework of the Polish Innovation Economy Operational Program (contract no. POIG.02.01.00-12-023/08).