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Liquid Crystals and their Application
Russian Journal

Zhidkie kristally i ikh prakticheskoe ispol'zovanie

Жидкие кристаллы и их практическое использование

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Rus Eng

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Zhidk. krist. ikh prakt. ispol'z. = Liq. Cryst. and their Appl., 2017, 17 (2), 14—20.
DOI: 10.18083/LCAppl.2017.2.14





Flexopolarization in the Vicinity of the Nematic Mesophase – Isotropic Liquid Phase Transition



O. A. Denisova

Author affiliations
Department of Physics, Ufa State Petroleum Technological University,
1 Kosmonavtov St., Ufa, 450062, Russia
E-mail: denisovaolga@bk.ru

Abstract
Flexoelectric effect in nematic liquid crystals was studied by modulation acoustic spectroscopy. A "sandwich" type cell, consisting of three plates separated by spacers, one of which is movable, was used. The movable spacer made shear vibrations in the horizontal plane. Thin layers of nematic liquid crystals with a homeotropic orientation of molecules and layer thickness of 20 to 100 μm were studied. The excitation frequency was 1 kHz. In the framework of the model proposed by De Gen, based on the Landau theory of phase transitions, the signal observed near the mesophase – isotropic liquid phase transition is of a flexoelectric nature and is due to a dipole mechanism. The temperature dependences of a piezoelectric signal induced by shear vibrations, the temperature influence on the value of the average constant angle of inclination
θ
c, and the oscillation amplitude
θ
d of the director of a liquid crystal were investigated. The dependences of the flexo-coefficients e33 on temperature for the studied liquid crystals, which demonstrate the role of dipole and quadrupole mechanisms in the observed molecular-orientation polarization, were also obtained. The relevance of the studied problem is connected with the possibility of creating liquid crystal displays or banners of a new generation. The use of liquid crystals offers a number of advantages (simplification of design, low power consumption, moderate overall dimensions and low cost).

Keywords: nematic liquid crystals, piezoelectric effect, flexoelectric polarization





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