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D. V. Shmeliova¹, E. P. Pozhidaev^1,2, 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
E-mail: s-p-a-s-m@mail.ru
²P. N. Lebedev Physical Institute,
53 Leninsky Pr., Moscow, 119991, Russia
E-mail: epozhidaev@mail.ru
³Hong Kong University of Science and Technology,
Clear Water Bay, Kowloon, Hong Kong
E-mail: eechigr@ust.hk

Abstract
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 γ_φ. 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