scholarly journals Orientational Instability Induced by the Electric Field in a Cell of a Nematic Liquid Crystal with Negative Dielectric Anisotropy

2017 ◽  
Vol 62 (9) ◽  
pp. 779-789
Author(s):  
A.I. Lesiuk ◽  
◽  
M.F. Ledney ◽  
O.S. Tarnavskyy ◽  
◽  
...  
Crystals ◽  
2020 ◽  
Vol 10 (2) ◽  
pp. 123 ◽  
Author(s):  
Rajratan Basu ◽  
Lukas J. Atwood ◽  
George W. Sterling

A small quantity of hexagonal boron nitride (h-BN) flakes is doped into a nematic liquid crystal (LC). The epitaxial interaction between the LC molecules and the h-BN flakes rising from the π−π electron stacking between the LC’s benzene rings and the h-BN’s honeycomb structure stabilizes pseudo-nematic domains surrounding the h-BN flakes. Electric field-dependent dielectric studies reveal that the LC-jacketed h-BN flakes follow the nematic director reorientation upon increasing the applied electric field. These anisotropic pseudo-nematic domains exist in the isotropic phase of the LC+h-BN system as well, and interact with the external electric field, giving rise to a nonzero dielectric anisotropy in the isotropic phase. Further investigations reveal that the presence of the h-BN flakes at a low concentration in the nematic LC enhances the elastic constants, reduces the rotation viscosity, and lowers the pre-tilt angle of the LC. However, the Fréedericksz threshold voltage stays mostly unaffected in the presence of the h-BN flakes. Additional studies show that the presence of the h-BN flakes enhances the effective polar anchoring strength in the cell. The enhanced polar anchoring strength and the reduced rotational viscosity result in faster electro-optic switching in the h-BN-doped LC cell.


2019 ◽  
Vol 9 (1) ◽  
Author(s):  
Jun-Yong Lee ◽  
Bohdan Lev ◽  
Jong-Hyun Kim

AbstractA carbon fibre is a rod-like microstructure, the longitudinal axis of which is aligned with the orientation of the director in a nematic liquid crystal. A nematic liquid crystal with negative dielectric anisotropy is mixed with carbon fibres. By applying an electric field perpendicular to the director, the carbon fibres tend to rotate in response to the electric field, and the directors around the carbon fibres tends to suppress the rotation. We control individual carbon fibres to obtain an expected orientation by handling the competition of two actions. The carbon fibre barely reacts in a small electric field. Meanwhile, when the threshold electric field is exceeded, the carbon fibre rotates with a steep gradient in the direction of the electric field. The change in the rotation shows little hysteresis. As the length of the carbon fibre is increased, the threshold electric field decreases. We analysed the above process with a theoretical model considering the response of the carbon fibre and liquid crystal. This study shows the possibility of accurate analogue orientation control of individual rod-like microstructures.


2020 ◽  
Vol 28 (3) ◽  
pp. 250-254
Author(s):  
M. Dencheva-Zarkova ◽  
G. B. Hadjichristov ◽  
Y. G. Marinov ◽  
I. A. Maslyanitsyn ◽  
A. G. Petrov ◽  
...  

1972 ◽  
Vol 33 (C1) ◽  
pp. C1-63-C1-67 ◽  
Author(s):  
M. BERTOLOTTI ◽  
B. DAINO ◽  
P. Di PORTO ◽  
F. SCUDIERI ◽  
D. SETTE

Crystals ◽  
2021 ◽  
Vol 11 (6) ◽  
pp. 605
Author(s):  
Ayushi Rastogi ◽  
Fanindra Pandey ◽  
Rajiv Manohar ◽  
Shri Singh

We report the effect of the doping of Cd1−xZnxS/ZnS core/shell quantum dots (CSQDs) in nematic liquid crystal p-methoxybenzylidenep-decylaniline (MBDA) at 0.05 wt/wt%, 0.1 wt/wt%, 0.15 wt/wt%, 0.2 wt/wt%, 0.25 wt/wt%, and 0.3 wt/wt% concentrations of CSQDs in MBDA. Dielectric parameters with and without bias with respect to frequency have been investigated. The change in electro-optical parameters with temperature has also been demonstrated. The increase in the mean dielectric permittivity was found due to the large dipole moment of CSQDs, which impose stronger interactions with the liquid crystal molecules. The dielectric anisotropy changes sign on doping CSQDs in MBDA liquid crystal. It was concluded that the CSQD doping noticeably increased the dielectric permittivity of nematic MBDA in the presence of an electric field. The doping of CSQDs in nematic MBDA liquid crystal reduced the ion screening effect effectively. This phenomenon is attributed to the competition between the generated ionic impurities during the assembling process and the ion trapping effect of the CSQDs. The rotational viscosity of nematic liquid crystal decreased with increasing concentration of the CSQDs, with a faster response time observed for the 0.05 wt/wt% concentration. The birefringence of the doped system increased with the inclusion of CSQDs in MBDA. These results find application in the field of display devices, phase shifters, LC – gratings, TIR waveguide, industries, and projectors.


2018 ◽  
Vol 173 ◽  
pp. 03002 ◽  
Author(s):  
Alexander Ayriyan ◽  
Edik Ayryan ◽  
Alexandre Egorov ◽  
Maria Dencheva-Zarkova ◽  
Georgi Hadjichristov ◽  
...  

A two-dimensional model of Fredericks effect was used for the investigation of the static electric field influence on nematic liquid crystal director orientation in the side-electrode cell. The solutions of the equations describing the model were obtained by finite-difference methods. Fredericks transition threshold for the central part of the cell, as well as dependencies of the distribution of the director orientation patterns on the electric field and location, were obtained. The numerical results are found to agree qualitatively with the experiment. Further investigations are needed to elucidate completely the Fredericks effect.


2002 ◽  
Vol 41 (Part 1, No. 7A) ◽  
pp. 4571-4576 ◽  
Author(s):  
Seung Ho Hong ◽  
Hyang Yul Kim ◽  
Jae-Hyung Kim ◽  
Sang-Hee Nam ◽  
Myong-Hoon Lee ◽  
...  

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