scholarly journals Magnetic field induced orientational transitions in liquid crystals doped with carbon nanotubes

2017 ◽  
Vol 8 ◽  
pp. 2807-2817 ◽  
Author(s):  
Danil A Petrov ◽  
Pavel K Skokov ◽  
Alexander N Zakhlevnykh
Keyword(s):  
Magnetic Field ◽  
Carbon Nanotubes ◽  
Liquid Crystal ◽  
Continuum Theory ◽  
Weakly Coupled ◽  
Transitions In Liquid Crystals ◽  
The Matrix ◽  
Liquid Crystal Matrix ◽  
Planar Phase ◽  
Orientational Transitions

We propose a continuum theory of orientational phase transitions induced by an external magnetic field in a suspension of carbon nanotubes in a nematic liquid crystal. It is shown that in a magnetic field a non-uniform and two different uniform phases are possible in the suspension. The uniform phases of the suspension differ by the type of orientational coupling of nanotubes with the liquid crystal matrix (the planar type when the nanotubes are oriented along the matrix director, and the homeotropic type when the nanotubes are perpendicular to the director). The possibility of a redistribution of the nanotube concentration (segregation effect) is shown. The fields of orientational transitions between uniform and non-uniform phases of the suspension are found analytically. It is shown that, when the nanotubes are weakly coupled to the matrix, the magnetic field induces reentrant transitions (uniform planar phase–non-uniform phase–uniform homeotropic phase–non-uniform phase). These transitions can be of first or of second order depending on the carbon nanotubes segregation intensity.

scholarly journals Magneto-orientation response of ferronematic with a tilted orientation of the director and magnetization

2021 ◽  
pp. 48-58
Author(s):  
Danil A. Petrov ◽  
◽  
Rifat R. Khannanov ◽  
Keyword(s):  
Magnetic Field ◽  
Liquid Crystal ◽  
Continuum Theory ◽  
Weak Magnetic Fields ◽  
Orientation Response ◽  
Analytical Expressions ◽  
Ferromagnetic Particles ◽  
Pretilt Angle ◽  
The Continuum ◽  
Orientational Transitions

The article considers orientational transitions induced by a magnetic field in a highly dispersed suspension of ferromagnetic particles in a nematic liquid crystal – ferronematic. We research the case when, in the absence of an external magnetic field between the directions of the liquid crystal director and magnetization of the impurity particles, a constant pretilt angle is maintained, and the coupling of the liquid crystal molecules to the surface of the ferroparticles is assumed to be soft and planar. An example of such an impurity is ferromagnetic carbon nanotubes magnetized at a certain angle to their long axes. On the basis of the continuum theory, the equilibrium values of the orientation angles of the liquid crystal director and magnetization are calculated for different values of the pretilt angle. The results of calculations are compared with the previously considered case of planar coupling between the director and magnetization. Analytical expressions are obtained for determining the orientational and magnetic structure of the ferronematic in the case of weak magnetic fields. The magnetization of the ferronematic is studied for different values of the pretilt angle.

scholarly journals Dynamic behavior of a nematic liquid crystal with added carbon nanotubes in an electric field

2018 ◽  
Vol 9 ◽  
pp. 233-241 ◽  
Author(s):  
Emil Petrescu ◽  
Cristina Cirtoaje
Keyword(s):  
Carbon Nanotubes ◽  
Relaxation Time ◽  
Liquid Crystal ◽  
Electric Field ◽  
Dynamic Behavior ◽  
Nematic Liquid Crystal ◽  
Relaxation Times ◽  
Continuum Theory ◽  
Pure Liquid ◽  
Significant Difference

The dynamic behavior of a nematic liquid crystal with added carbon nanotubes (CNTs) in an electric field was analyzed. A theoretical model based on elastic continuum theory was developed and the relaxation times of nematic liquid crystals with CNTs were evaluated. Experiments made with single-walled carbon nanotubes dispersed in nematic 4-cyano-4’-pentylbiphenyl (5CB) indicated a significant difference of the relaxation time when compared to pure liquid crystal. We also noticed that the relaxation time when the field is switched off depends on how long the field was applied. It is shorter when the field is switched off immediately after application and longer when the field was applied for at least one hour.

scholarly journals Exploring the alignment of carbon nanotubes dispersed in a liquid crystal matrix using coplanar electrodes

2015 ◽  
Vol 117 (12) ◽  
pp. 125303 ◽  
Author(s):  
D. Volpati ◽  
M. K. Massey ◽  
D. W. Johnson ◽  
A. Kotsialos ◽  
F. Qaiser ◽  
...  
Keyword(s):  
Carbon Nanotubes ◽  
Liquid Crystal ◽  
Crystal Matrix ◽  
Liquid Crystal Matrix ◽  
Coplanar Electrodes

scholarly journals Electrical response of liquid crystal cells doped with multi-walled carbon nanotubes

2015 ◽  
Vol 6 ◽  
pp. 396-403 ◽  
Author(s):  
Amanda García-García ◽  
Ricardo Vergaz ◽  
José Francisco Algorri ◽  
Xabier Quintana ◽  
José Manuel Otón
Keyword(s):  
Carbon Nanotubes ◽  
Liquid Crystal ◽  
Electric Field ◽  
Electrical Response ◽  
Characteristic Impedance ◽  
Self Organized ◽  
The Matrix ◽  
Multi Walled Carbon Nanotubes ◽  
Elongated Nanoparticles ◽  
Walled Carbon Nanotubes

The inclusion of nanoparticles modifies a number of fundamental properties of many materials. Doping of nanoparticles in self-organized materials such as liquid crystals may be of interest for the reciprocal interaction between the matrix and the nanoparticles. Elongated nanoparticles and nanotubes can be aligned and reoriented by the liquid crystal, inducing noticeable changes in their optical and electrical properties. In this work, cells of liquid crystal doped with high aspect ratio multi-walled carbon nanotubes have been prepared, and their characteristic impedance has been studied at different frequencies and excitation voltages. The results demonstrate alterations in the anisotropic conductivity of the samples with the applied electric field, which can be followed by monitoring the impedance evolution with the excitation voltage. Results are consistent with a possible electric contact between the coated substrates of the LC cell caused by the reorientation of the nanotubes. The reversibility of the doped system upon removal of the electric field is quite low.

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.

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