Magnetic segregation effect in liquid crystals doped with carbon nanotubes

• Danil A. Petrov,
• Pavel K. Skokov,
• Alexander N. Zakhlevnykh and
• Dmitriy V. Makarov

Beilstein J. Nanotechnol. 2019, 10, 1464–1474, doi:10.3762/bjnano.10.145

• 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

• anisotropy of the diamagnetic susceptibility, this leads to a decrease in the critical fields of magnetic [27][28] and electric [14][16][26][29][30] Fréedericksz transition (a threshold process of changing the orientational structure inside an NLC layer under the action of external fields [31]). Experiments

Effect of ferroelectric BaTiO₃ particles on the threshold voltage of a smectic A liquid crystal

• Abbas R. Imamaliyev,
• Mahammadali A. Ramazanov and
• Shirkhan A. Humbatov

Beilstein J. Nanotechnol. 2018, 9, 824–828, doi:10.3762/bjnano.9.76

• electric field [10]. The Fréedericksz transition occurs at least in two stages when the BaTiO3 nanoparticles are added to the liquid crystal [11][12]. In colloids of ferroelectric particles in nematic LCs, as a rule, oleic acid is present as a stabilizer, the role of which is to prevent the aggregation of

Dynamic behavior of nematic liquid crystal mixtures with quantum dots in electric fields

• Emil Petrescu,
• Cristina Cirtoaje and
• Octavian Danila

Beilstein J. Nanotechnol. 2018, 9, 399–406, doi:10.3762/bjnano.9.39

• on a sample containing 0.89% (mass fraction) of CdSe/ZnS quantum dots revealed a decrease of the relaxation time compared to pure 5CB. Keywords: Fréedericksz transition; nematic liquid crystals; quantum dots; Introduction The expansion of liquid crystal (LC)-based devices in common life domains as

• than the Fréedericksz transition threshold [18][19] is applied transversely to a planar liquid crystal cell, the molecules change their orientation tending to align their director in parallel to the field. This reorientation is illustrated by an intensity variation of a laser beam crossing through the

• -based device parameters. Theoretical Background When a nematic liquid crystal with positive dielectric anisotropy is exposed to an electric field, and if the intensity of the field is higher than the Fréedericksz transition threshold, the molecular director changes its orientation, trying to align in

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

• Emil Petrescu and
• Cristina Cirtoaje

Beilstein J. Nanotechnol. 2018, 9, 233–241, doi:10.3762/bjnano.9.25

• : Fréedericksz transition, nanotubes; Introduction The increased interest for nanomaterials in different domains such as chemistry, medicine or engineering, makes their characterization quite necessary. This might be the reason why there are so many research papers presenting new materials and new experiments

• molecules and align themselves parallel with the long axis of the nematic [12][13][14]. Under the action of an external magnetic or electric field above a critical threshold, nematic molecules collectively change their orientation. This is called the Fréedericksz transition [15][16] and the molecular

• -cyano-4’-pentylbiphenyl (5CB) liquid crystal (LC). Theoretical Background When a liquid crystal with positive dielectric anisotropy is exposed to an external electric field higher than the critical Fréedericksz transition threshold, its molecules have a tendency to orient their director parallel to the

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

• Danil A. Petrov,
• Pavel K. Skokov and
• Alexander N. Zakhlevnykh

Beilstein J. Nanotechnol. 2017, 8, 2807–2817, doi:10.3762/bjnano.8.280

• , one should expect decreasing of the threshold field of the magnetic Fréedericksz transition, which is confirmed by experiment [18][19], as well as a decrease in the electric field of the Fréedericksz transition [11][14][20][21][22]. Along with this, there are experimental studies devoted to the

• . This effect is known as the Fréedericksz transition [32]. CNTs are also oriented by the magnetic field, because they possess an anomalously strong diamagnetism and positive diamagnetic anisotropy [10][33][34][35], so even small concentrations of CNTs in suspension should lead to a decreasing of the

• Fréedericksz transition threshold in comparison with the pure NLC. These two mechanisms of the field influence on the suspension prove to be interdependent due to the orientational interaction of CNTs with the LC matrix. In the framework of continuum theory, the equilibrium state of the suspension corresponds

Dynamic behavior of a nematic liquid crystal mixed with CoFe₂O₄ ferromagnetic nanoparticles in a magnetic field

• Emil Petrescu,
• Cristina Cirtoaje and
• Cristina Stan

Beilstein J. Nanotechnol. 2017, 8, 2467–2473, doi:10.3762/bjnano.8.246

• and only a small distortion angle of the liquid crystal molecular director is observed. A comparison with a previously developed theoretical model confirms this small deviation. Keywords: ferromagnetic nanoparticles; Fréedericksz transition; Introduction Currently, there is a high interest in the

• reason is the long response time of liquid crystals to the field action. The second reason is the high threshold for the Fréedericksz transition, which requires powerful DC voltage sources and large electromagnets. By using ferromagnetic particles, the response time can be reduced, but at the cost of a

• the support area. This new structure obtained inside the cell exhibits a different Fréedericksz transition and a shorter response time compared to a pure 5CB nematic cell. Theoretical background Nematic liquid crystals are uniaxial crystals. When placed between crossed polarizers and passed through by