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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., 2018, 18 (4), 88—94.
DOI: 10.18083/LCAppl.2018.4.88

Capillary Flow and Shear Viscosity of Ferroelectric Liquid Crystal

D. V. Shmeliova1, E. P. Pozhidaev1,2, S. S. Kharlamov1, S. V. Pasechnik1, V. A. Barbashov2, V. G. Chigrinov3

Author affiliations
1MIREA – Russian Technological University, Problem Laboratory of Molecular Acoustics,
78 Vernadsky Av., Moscow, 119454, Russia
2P. N. Lebedev Physical Institute,
53 Leninsky Pr., Moscow, 119991, Russia
3Hong Kong University of Science and Technology,
Clear Water Bay, Kowloon, Hong Kong

Experimentally shown that the shear flow of a ferroelectric smectic C* liquid crystal (FLC) in flat capillary with homeotropic boundary conditions can be described in the framework of the Newtonian fluids theory if the pitch p0 of the FLC helix is much less than the capillary gap. The motion of the contact line during the filling of the capillary was recorded in the experiment and compared with the theory, which made it possible to estimate the shear viscosity coefficient η ≈ 0.5 Pa·s, which turned out to be much larger than the rotational viscosity coefficient γφ. In the capillary filling process, the principal optical axis of the FLC helical structure was oriented mainly perpendicular to the substrates, and the smectic layers were parallel to the substrates. At the same time, narrow dislocation bands arose along the flow direction. The principal optical axis deviated from the normal to the substrates at different angles within the dislocation bands. The total area occupied by dislocations does not exceed 5 % of the flow area; therefore, dislocations do not have a significant effect on the rheological behavior of the smectic C* phase.

Keywords: ferroelectric liquid crystal, capillary shear flow, shear viscosity

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