scholarly journals Magnetic segregation effect in liquid crystals doped with carbon nanotubes

2019 ◽  
Vol 10 ◽  
pp. 1464-1474 ◽  
Author(s):  
Danil A Petrov ◽  
Pavel K Skokov ◽  
Alexander N Zakhlevnykh ◽  
Dmitriy V Makarov
Keyword(s):  
Magnetic Field ◽  
Carbon Nanotubes ◽  
Liquid Crystal ◽  
Phase Lag ◽  
Freedericksz Transition ◽  
Planar Texture ◽  
Segregation Effect ◽  
Fréedericksz Transition ◽  
The Magnetic Field ◽  
Crystal Composite

We study the orientational transitions in a suspension of carbon nanotubes in a nematic liquid crystal induced by an external magnetic field. The case of a finite orientational anchoring of liquid crystal molecules at the surface of doped carbon nanotubes is considered. It is shown that in a magnetic field the initial homogeneous planar texture of the liquid crystal–carbon nanotubes mixture is disturbed in a threshold manner (Fréedericksz transition). The orientational and concentration distributions of the suspension are studied for different values of the magnetic field strength and segregation intensity of the impurity subsystem. The optical phase lag between ordinary and extraordinary rays of light transmitted through a layer of a liquid crystal composite is calculated. The possibility of changing the nature of the Fréedericksz transition from second order to first order is shown. This tricritical behavior is related to the redistribution of the carbon nanotubes (segregation effect) inside the layer.

scholarly journals Bifurcation analysis of the twist-Fréedericksz transition in a nematic liquid-crystal cell with pre-twist boundary conditions

2009 ◽  
Vol 20 (3) ◽  
pp. 269-287 ◽  
Author(s):  
FERNANDO P. DA COSTA ◽  
EUGENE C. GARTLAND ◽  
MICHAEL GRINFELD ◽  
JOÃO T. PINTO
Keyword(s):  
Magnetic Field ◽  
Liquid Crystal ◽  
Boundary Conditions ◽  
Nematic Liquid Crystal ◽  
Pitchfork Bifurcation ◽  
Critical Magnetic Field ◽  
Twist Boundary ◽  
Freedericksz Transition ◽  
Diamagnetic Anisotropy ◽  
Fréedericksz Transition

Motivated by a recent investigation of Millar and McKay [Director orientation of a twisted nematic under the influence of an in-plane magnetic field. Mol. Cryst. Liq. Cryst435, 277/[937]–286/[946] (2005)], we study the magnetic field twist-Fréedericksz transition for a nematic liquid crystal of positive diamagnetic anisotropy with strong anchoring and pre-twist boundary conditions. Despite the pre-twist, the system still possesses ℤ2 symmetry and a symmetry-breaking pitchfork bifurcation, which occurs at a critical magnetic-field strength that, as we prove, is above the threshold for the classical twist-Fréedericksz transition (which has no pre-twist). It was observed numerically by Millar and McKay that this instability occurs precisely at the point at which the ground-state solution loses its monotonicity (with respect to the position coordinate across the cell gap). We explain this surprising observation using a rigorous phase-space analysis.

scholarly journals The Freedericksz Transition in a Spatially Varying Magnetic Field

Crystals ◽  
2021 ◽  
Vol 11 (5) ◽  
pp. 541
Author(s):  
Tianyi Guo ◽  
Xiaoyu Zheng ◽  
Peter Palffy-Muhoray
Keyword(s):  
Magnetic Field ◽  
Cylindrical Symmetry ◽  
Central Plane ◽  
Freedericksz Transition ◽  
Radial Magnetic Field ◽  
Director Field ◽  
Electric And Magnetic Fields ◽  
Fréedericksz Transition ◽  
Spatially Varying ◽  
The Magnetic Field

Much is known about the Freedericksz transition induced by uniform electric and magnetic fields in nematic liquid crystals. In this work, we are interested in the effects of a spatially varying field on the transition. Specifically, we study the director configuration in a homeotropic nematic cell in a spatially varying magnetic field with cylindrical symmetry. The experiment is conducted with a ring magnet which provides a radial magnetic field with magnitude monotonically decreasing to zero at the center. The nematic cell is positioned in the central plane of the ring, with the cell normal parallel to the ring normal. Interference patterns of the nematic cell between crossed polarizers were observed. The director configuration in the nematic cell is modeled with Frank–Oseen theory, and the computed interference pattern from the simulated director field are compared with experiment. We conclude that if the magnetic field strength varies with position in the plane of the cell, there is no Freedericksz transition.

Interactions Between Carbon Nanotubes and Liquid Crystals in Binary Nematic Electro-Optic Cells

2009 ◽  
Vol 1228 ◽  
Author(s):  
Georgi Yordanov Georgiev ◽  
Erin A Gombos ◽  
Michael B McIntyre ◽  
Michael F Mattera ◽  
Peter A. Gati ◽  
...  
Keyword(s):  
Carbon Nanotubes ◽  
Liquid Crystal ◽  
Electric Field ◽  
Electromagnetic Radiation ◽  
Azimuthal Angle ◽  
Freedericksz Transition ◽  
Multiwalled Carbon ◽  
Complete Control ◽  
Electro Optic ◽  
Fréedericksz Transition

AbstractWe studied the effects of multiwalled carbon nanotubes (MWCNTs) on the Freedericksz transition of a liquid crystal (LC) and calibrated the altitudinal angle of CNTs as a function of the electric field. In addition, we directed the azimuthal angle which gave us complete control of the 3D orientation of the CNTs. We constructed anti-parallel electro-optic cells using a nanocomposite at a concentration of 0.01% CNTs with 4-Cyano-4'-pentylbiphenyl (5CB) liquid crystal. This low concentration was necessary to achieve maximum transmission of electromagnetic radiation through the cell and to minimize the Van der Waals attraction between the CNTs responsible for their aggregation. We chose two dimensional microscopic transmission ellipsometry (2D-MTE) to measure the phaseshift of the polarized electromagnetic radiation through the cell and to derive from it the altitudinal angle of the CNTs. Our results show that in the presence of CNTs the Freedericksz transition occurs at 55% of the transitional electric field as compared to the control electro-optic cell without CNTs. The width of the Freedericksz transition narrows by a similar factor. The switching time of the cell decreased in the presence CNTs by 18.5%.

Magnetic-Field-Induced Freedericksz Transition of a Homeotropical Alignment Liquid Crystal Doped with Double-Azo

1999 ◽  
Vol 38 (Part 1, No. 10) ◽  
pp. 6017-6018 ◽  
Author(s):  
Ying Xiang ◽  
textscLin Ziyang ◽  
textscLi Tao ◽  
textscLiang Xuxia ◽  
textscZhang Jieli ◽  
...  
Keyword(s):  
Magnetic Field ◽  
Liquid Crystal ◽  
Freedericksz Transition ◽  
Fréedericksz Transition

Magnetic field induced Freedericksz transition of a planar aligned liquid crystal doped with metalloporphyrins FeTPPCl, MnTPPCl and ZnTPP

2000 ◽  
Vol 27 (2) ◽  
pp. 211-214 ◽  
Author(s):  
Xiang Ying ◽  
Shi Jue ◽  
Lin Ziyang ◽  
Li Tao ◽  
Jin-Wang Huang ◽  
...  
Keyword(s):  
Magnetic Field ◽  
Liquid Crystal ◽  
Freedericksz Transition ◽  
Fréedericksz Transition

scholarly journals Dynamics of a liquid crystal close to the Fréedericksz transition

2013 ◽  
Vol 104 (2) ◽  
pp. 26004 ◽  
Author(s):  
A. Caussarieu ◽  
A. Petrosyan ◽  
S. Ciliberto
Keyword(s):  
Liquid Crystal ◽  
Freedericksz Transition ◽  
Fréedericksz Transition
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