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Open AccessArticle

Dielectric Properties of Chiral Ferroelectric Liquid Crystalline Compounds with Three Aromatic Rings Connected by Ester Groups

1
Department of Physics, University of North Bengal, Siliguri 734013, West Bengal, India
2
Department of Physics, Siliguri Institute of Technology, Siliguri 734013, India
3
Institute of Physics of the Czech Academy of Sciences, 18221 Prague, Czech Republic
*
Author to whom correspondence should be addressed.
Crystals 2019, 9(9), 473; https://doi.org/10.3390/cryst9090473
Received: 12 August 2019 / Revised: 1 September 2019 / Accepted: 7 September 2019 / Published: 10 September 2019
(This article belongs to the Special Issue Ferroelectric and Ferromagnetic Liquid Crystals)
The tilted ferroelectric SmC* phase of three structurally different series having three aromatic rings in the core structure connected by ester groups with different end alkyl chain lengths, all of which are derived from lactic acid, have been observed by broadband dielectric spectroscopy. Introduction of structural variations within the liquid crystalline compounds has led to the formation of chiral nematic N*, or the paraelectric orthogonal SmA* phase at higher temperatures. The dielectric spectra strongly depend both on the temperature as well as the specific molecular structure of the self-assembling compounds possessing the ferroelectric polar order. The results reveal a strong Goldstone mode in the ferroelectric SmC* phase with ~kHz relaxation frequency. In the SmC* phase, the real and imaginary parts of the complex permittivity increase up to certain temperature near the SmC*-N*/SmA* transition and then decrease with increasing temperature, perhaps due to the disruption of the molecular domains at the onset of the SmA*/N* phase transition. The dielectric strength attains a maximum value in the SmC* phase and then decreases near the SmA*/N* phase transition. The dielectric strength is also influenced by the lengths of the alkyl chain and the nature of the connecting unit of the constituent molecules. The relaxation time and the relaxation frequency are found to vary with the molecular structure of the studied ferroelectric compounds. View Full-Text
Keywords: ferroelectric liquid crystals; lactic acid derivative; dielectric spectroscopy; dielectric strength; relaxation time; structure-property correlations ferroelectric liquid crystals; lactic acid derivative; dielectric spectroscopy; dielectric strength; relaxation time; structure-property correlations
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MDPI and ACS Style

Das, M.K.; Barman, B.; Das, B.; Hamplová, V.; Bubnov, A. Dielectric Properties of Chiral Ferroelectric Liquid Crystalline Compounds with Three Aromatic Rings Connected by Ester Groups. Crystals 2019, 9, 473.

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