Effect of Inhomogeneous Electric Field in a Cell with Side Electrodes: Nematic Liquid Crystal 5CB
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Effect of Inhomogeneous Electric Field in a Cell with Side Electrodes: Nematic Liquid Crystal 5CB M. Dencheva-Zarkovaa, G. B. Hadjichristova, Y. G. Marinova, I. A. Maslyanitsynb, A. G. Petrova, L. Popovaa, V. D. Shigorinb, *, and S. I. Torgovac aGeorgi
Nadjakov Institute of Solid State Physics, Bulgarian Academy of Sciences, Sofia, 1784 Bulgaria Prokhorov General Physics Institute of the Russian Academy of Sciences, Moscow, 119991 Russia c Lebedev Physical Institute, Russian Academy of Sciences, Moscow, 119991 Russia *e-mail: [email protected]
b
Received September 17, 2019; revised October 18, 2019; accepted November 21, 2019
Abstract—The influence of the geometry of a cell with side electrodes and the parameters of applied pulsedperiodic voltage on the director orientation in nematic liquid crystal 5CB is analyzed. It is shown that the twodimensional model of director motion taking into account the electric field inhomogeneity in the cell provides satisfactory agreement with experimental results. DOI: 10.3103/S1541308X2003005X
1. INTRODUCTION Nematic liquid crystals (NLCs) have long been successfully used in technical devices of various types [1, 2]. This fact stimulates a search for new applications of NLCs and materials on their basis, as well as the development and modification of the corresponding investigation methods. Cells with side electrodes must be used in a number of electro-optic studies of homeotropically (planarly) oriented liquid crystals with positive (negative) dielectric anisotropy [3–7]. Previously, when carrying out experiments on secondharmonic generation (SHG) with such cells, we observed a number of specific features. The study of SHG in samples of homeotropically oriented NLC npentyl-n'-cyanobiphenyl (5CB) under a pulsed-periodic electric field revealed the existence of regions with significantly different director orientations and relatively sharp boundaries. This finding was confirmed by polarization microscopy: “dark” and “bright” domains were observed in the LC cell [8, 9]. In this paper, we report the results of a theoretical analysis of this domenization with allowance for the type of electric field and the cell geometry. The analysis is based on the results of our experiments with NLC 5CB.
The symmetry of the cell under study differs from that analyzed in [1]. In this case, reverse liquid flow (see [1]) is absent: one of the component of its velocity vector V is zero due to the symmetry of the problem under consideration, and the other two components (oriented perpendicular to the electrode planes and to the plane of glass plates, respectively) are zero (according to the continuity equation). For this reason, we used the Erickson‒Leslie equation [10] with allowance for the 2D character of the problem and the absence of reverse flow [11]:
K ( θ xx + θ yy ) + 1 ε0ΔεE 2 sin ( 2θ) = γ1 ∂θ , 2 ∂t Y d/2 T
n X
E –d/2
2. EQUATIONS IN USE Calculations were performed for an LC cell of thickness d and interelectrode distance L. The cell cross section is presented in
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