How to change the sensitivity of liquid crystals in external magnetic field

2012 ◽  
Vol 48 (2) ◽  
pp. 407-414 ◽  
Keyword(s):  
Magnetic Field ◽  
Liquid Crystals ◽  
External Magnetic Field

Numerical investigation of influence of ionic space charge and flexoelectric polarization on measurements of elastic constants in nematic liquid crystals

2009 ◽  
Vol 17 (2) ◽  
Author(s):  
M. Buczkowska ◽  
G. Derfel ◽  
M. Konowalski
Keyword(s):  
Magnetic Field ◽  
Liquid Crystal ◽  
Liquid Crystals ◽  
External Magnetic Field ◽  
Space Charge ◽  
Elastic Constants ◽  
High Concentration ◽  
Light Passing ◽  
The Magnetic Field

AbstractDeformations of nematic layers caused by magnetic field allow determination of the elastic constants of liquid crystal. In this paper, we simulated numerically the deformations of planar and homeotropic nematic layers. The flexoelectric properties of the nematic and presence of ions were taken into account. Our aim was to show the influence of flexoelectricity on the results of the real measurement of the elastic constants k33 and k11. In these simulations, we calculated the optical phase difference ΔΦ between the ordinary and extraordinary rays of light passing through the layer placed between crossed polarizers as a function of the magnetic field induction B. One of the elastic constants can be calculated from the magnetic field threshold for deformation. The ratio k33/k11 can be found by means of fitting theoretical ΔΦ(B) dependence to the experimental results. The calculations reveal that the flexoelectric properties influence the deformations induced by the external magnetic field. In the case of highly pure samples, this may lead to false results of measurement of the elastic constants ratio k33/k11. This influence can be reduced if the nematic material contains ions of sufficiently high concentration. These results show that the flexoelectric properties may play an important role, especially in well purified samples.

Nonreciprocal localization of light in magnetoactive cholesteric liquid crystals in an external magnetic field

Optik ◽  
2021 ◽  
Vol 247 ◽  
pp. 167927
Author(s):  
A.H. Gevorgyan ◽  
S.S. Golik ◽  
Y.N. Kulchin ◽  
N.A. Vanyushkin
Keyword(s):  
Magnetic Field ◽  
Liquid Crystals ◽  
External Magnetic Field ◽  
Cholesteric Liquid Crystals

scholarly journals How to Enhance Sensitivity of Liquid Crystals to External Magnetic Field?

2015 ◽  
Vol 127 (2) ◽  
pp. 157-162 ◽  
Author(s):  
P. Kopčanský ◽  
N. Tomašovičová ◽  
V. Gdovinová ◽  
M. Timko ◽  
N. Éber ◽  
...  
Keyword(s):  
Magnetic Field ◽  
Liquid Crystals ◽  
External Magnetic Field

NMR Field-Cycling Study of Rotational Flow and Viscosity in Nematic Liquid Crystals

1994 ◽  
Vol 49 (12) ◽  
pp. 1179-1187 ◽  
Author(s):  
H. Gotzig ◽  
S. Grunenberg-Hassanein ◽  
F. Noack
Keyword(s):  
Magnetic Field ◽  
Liquid Crystals ◽  
External Magnetic Field ◽  
Rotational Flow ◽  
Magnetic Field Direction ◽  
Initial Field ◽  
Diamagnetic Anisotropy ◽  
Polymer Liquid Crystals ◽  
Field Cycling ◽  
Fast Electronic

Abstract A proton NMR method is described which enables rotational flow and viscosity measurements of low molecular weight ṉematic ḻiquid c̱rystals (NLC's). This is achieved by an extension of the common NMR field-cycling technique, namely by fast electronic switching of both the external magnetic field direction and strength. In thermodynamic equilibrium, the director of an NLC with positive diamagnetic anisotropy (Δχ > 0) orients parallel to the external magnetic field. Thus a change of this direction causes a reorientation process of the molecules to align to the new equilib­rium, which in low viscous systems in contrast to polymer liquid crystals is rather fast and hence requires fast field switching. We have studied systematically this response as a function of the initial field rotation angle 90 relative to the director for some homologous NLC's of the n-alkyl-cyano-biphenyl (nCB) series. It is shown that there exists a critical angle θcr in such a way that for θo < θcr, however (e.g. in the case of 5 CB θcr is ≈ 85 degrees) the viscoelastic behaviour is more complicated because of a coupling between flow and director gradients. The analysis of the alignment process by the changes of the proton line spectra also allows to determine the Leslie viscosities α1, α2, α3, α4 + α5, and the average Frank elastic constant K̄ by a single measurement.

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