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Timofey P. Tkachenko*, Vadim A. Barbashov, Evgeny P. Pozhidaev

Author affiliations
Р. N. Lebedev Physical Institute of the Russian Academy of Sciences, Moscow, Russia
*Corresponding author: tptkachenko@lebedev.ru

Abstract
The effect of non-mesogenic chiral additives, such as (S,S)-bis-(1,1,1-trifluoro-oct-2-yl)-4,4"-terphenyl-dicarboxylate (FODTA-6) and (S,S)-(1-butoxy-1-oxo-propan-2-yl)-[1,1':4'1"-terphenyl]-4,4″-dicarboxylate (SS-LACT-4), on the properties of ferrielectric liquid crystal (FiLC) mixtures FerriLCM-1 and FerriLCM-2 was investigated. FODTA-6 induced a positive sign for spontaneous polarization and handedness in mixtures of polar smectic C* liquid crystals, while SS-LACT-4 induced a positive sign for spontaneous polarization but a negative sign for handedness. A non-chiral smectic C liquid crystal 2-(4'-pentylbiphenyl-4'-yl)-5-hexyl pyrimidine (BPP-65) was used as a matrix. It was found that the absence of the chiral SS-LACT-4 dopant in FerriLCM-2 mixture resulted in a significant change of dielectric and electro-optical properties of the FiLC. In FerriLCM-2 mixture, several parameters decreased compared to FerriLCM-1: spontaneous polarization, electro-optical response time, rotational viscosity, electric susceptibility, and orientational Kerr-effect coefficient K_Kerr. At the same time the electric critical fields E_cp1 and E_cp2 significantly increased. Within the framework of the existing phenomenological theory of chiral smectics C*, a quadratic dependence between orientational Kerr-effect coefficient and free relaxation time of helical structure was obtained. This quadratic relationship has been experimentally confirmed, yet it was also demonstrated that there are significant quantitative discrepancies between experimental data and theoretical calculations for FiLCs.

Keywords: ferrielectric liquid crystals, liquid crystal mixtures, electro-optics, orientational Kerr-effect