FREEDERICKSZ TRANSITION IN PRETILTED NEMATIC CELLS IN THE MAGNETIC FIELD NORMAL TO THE DIRECTOR

1979 ◽  
Vol 40 (C3) ◽  
pp. C3-519-C3-524 ◽  
Author(s):  
H. ONNAGAWA ◽  
M. KUWAHARA ◽  
K. MIYASHITA
Keyword(s):  
Magnetic Field ◽  
Freedericksz Transition ◽  
Fréedericksz Transition ◽  
The Magnetic Field

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.

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 Fréedericksz transition in a periodic magnetic field

1988 ◽  
Vol 38 (5) ◽  
pp. 2641-2649 ◽  
Author(s):  
M. C. Torrent ◽  
F. Sagués ◽  
F. Arias ◽  
M. San Miguel
Keyword(s):  
Magnetic Field ◽  
Freedericksz Transition ◽  
Periodic Magnetic Field ◽  
Fréedericksz Transition

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.

Static and Dynamic Behavior of Ferronematics Under Magnetic Fields

1998 ◽  
Vol 12 (13) ◽  
pp. 529-540 ◽  
Author(s):  
Cornelia Motoc ◽  
Emil Petrescu
Keyword(s):  
Dynamic Behavior ◽  
Threshold Field ◽  
Relaxation Processes ◽  
Relaxation Phenomena ◽  
Electrical Measurements ◽  
Freedericksz Transition ◽  
Fréedericksz Transition ◽  
Electrical Methods ◽  
The Magnetic Field ◽  
Good Agreement

The static and dynamic behavior under magnetic elds of ferronematics obtained by adding an organomagnetic material to the nematic E3 is investigated. First, by using both optical and electrical measurements, an increase of the threshold field for magnetic Freedericksz transition was noticed. Second, we examined both theoretically and experimentally the relaxation phenomena occurring in these ferronematics when the magnetic field was suddenly varied. We found that for ferronematics the relaxation processes are delayed when compared to those occurring in pure nematics. The threshold fields for magnetic Freedericksz transition were determined by means of the relaxation time and the results are in good agreement with the ones obtained when using the optical and electrical methods reported before.

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