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Current issue   Ukr. J. Phys. 2017, Vol. 62, N 5, p.392-401
https://doi.org/10.15407/ujpe62.05.0392    Paper

Lesiuk A.I., Ledney M.F., Tarnavskyy O.S.

Taras Shevchenko National University of Kyiv
(4, Prosp. Academician Glushkov, Kyiv 03127, Ukraine; e-mail: lesyuk.andrey@gmail.com, ledney@univ.kiev.ua, smalko1@bigmir.net)

Instability of Director Orientation in a Planar Nematic Cell under Tunable Boundary Conditions in the Electric Field

Section: Soft Matter
Original Author's Text: Ukrainian

Abstract: The planar-planar director reorientation in a nematic liquid crystal (NLC) cell by an external static electric field has been studied. The gliding of the NLC director easy axis over the polymer substrate due to the interaction between the easy axis and the electric field is taken into account. The contribution of this interaction to the surface free energy of the system is assumed to be linear in the electric field, if the elastic fragments of substrate polymer molecules possess their own dipole moments. If the dipole moments of the elastic fragments of polymer molecules are induced by the electric field, the corresponding contribution is taken to be quadratic in the electric field. Depending on the character of the interaction between the easy axis and the electric field, the orientation instability of the director is shown to either have a threshold or not. In both cases, the dynamics of the director and the easy axis has been analyzed, by starting from the field switching-on time moment, during the transition of the system to a stationary state, and until the field is switched-off and the system returns to the initial homogeneous state.

Key words: nematic liquid crystal, orientational instability, easy axis gliding, director evolution, switching-on/off time, Fr´eedericksz transition threshold.