Ferromagnetic Carbon Nanotubes Research Articles

Investigation of Ferromagnetic Nanoparticles’ Behavior in a Radio Frequency Electromagnetic Field for Medical Applications

This work raises the hypothesis that it is possible to use ferromagnetic carbon nanotubes filled with iron to hyperthermally destroy cancer cells in a radiofrequency electromagnetic field. This paper describes the synthesis process of iron-filled multi-walled carbon nanotubes (Fe-MWCNTs) and presents a study of their magnetic properties. Fe-MWCNTs were synthesized by catalytic chemical vapor deposition (CCVD). Appropriate functionalization properties of the nanoparticles for biomedical applications were used, and their magnetic properties were studied to determine the heat generation efficiency induced by exposure of the particles to an external electromagnetic field. The response of the samples was measured for 45 min of exposure. The results showed an increase in sample temperature that was proportional to concentration. The results of laboratory work were compared to the simulation using COMSOL software.

Orientational Transitions in Magnetically Compensated Liquid-Crystal Suspensions of Ferromagnetic Carbon Nanotubes

Purpose of research is to study the influence of ferromagnetic carbon nanotubes on orientational transitions in magnetically compensated liquid-crystal suspensions.Methods. The problem was solved in the framework of the continuum theory. By minimizing the Helmholtz free energy functional, a system of Lagrange-Euler equations is obtained that determines the equilibrium dependences of the orientation angles of liquid crystal and impurity ferromagnetic carbon nanotubes directors, as well as the concentration distributions of the dispersed phase of the suspension as a function of the transverse coordinate, material parameters, and magnetic field strength.Results. It is shown that in the presence of an external magnetic field, a liquid-crystal suspension of ferromagnetic carbon nanotubes can be in a non-uniform phase (angular phase) and two uniform phases (planar and homeotropic phases). Expressions for the threshold fields of transitions between coexisting orientational phases are obtained analytically as functions of the material parameters of the composite. Diagrams of the orientational phases of the suspension are plotted.Conclusion. As a result of the research, it was shown that the addition of low concentrations of ferromagnetic carbon nanotubes can significantly reduce the threshold of the magnetic Fréedericksz transition compared to a pure liquid crystal, which is important for various technical applications. The obtained analytical formulas for the threshold fields of transitions between different orientational phases can be used to determine the anchoring energy and material parameters of suspensions of ferromagnetic carbon nanotubes in a liquid crystal.

Optimization of Mass Flow in the Synthesis of Ferromagnetic Carbon Nanotubes in Chemical Vapor Deposition System.

Carbon nanotubes have unique properties, which make it possible to be applied in a variety of sensing applications. Moreover, by controlling the synthesis chemistry process, it is possible for carbon nanotubes to either fill or attach to its surface metal particles, e.g., iron. In an industrial scale, the yield and purity of the final product is very important. This work describes the chemical vapor deposition (CVD) method of carbon iron nanocontainers with maximum nanoparticles to impurities ratio. As one of the main parameters, the mass flow of gases was considered. To investigate the quality of the product, the scanning electron microscopy and thermogravimetric methods were used. Results for different process conditions were presented and discussed. The low gas velocity and high temperatures may affect the catalyst decomposition and ionization. The optimum flow and temperature in the reactor were determined.

Магнитоориентационный отклик ферронематика с наклонным сцеплением директора и намагниченности

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.

Self-Assembly Prepared Millimeter Length Ferromagnetic Carbon Nanotubes with Spin Nontrivial Electronic Transport Properties

Exploring the spin degree of freedom in electronic transport of carbon-based materials, such as carbon nanotubes (CNTs), is of interest from the point of view of materials and applications. However...

Influence of Ferromagnetic Carbon Nanotubes on Magnetic Transitions in Liquid Crystals

Magnetic field-induced orientational transitions in suspensions of carbon nanotubes (CNTs) in nematic liquid crystals have been studied in the framework of a continuum theory. Ferromagnetic CNTs are considered that possess, in addition to a large anisotropy of diamagnetic susceptibility, an additional magnetic moment due to ferromagnetic particles either situated on the CNT surface or encapsulated inside. It is established that, depending on the energy of coupling between disperse CNTs and liquid-crystalline matrix, the external magnetic field induces various sequences of orientational transitions. A threshold value of the coupling energy is determined, above which a transition from the initial homogeneous planar phase to inhomogeneous state (angular phase) becomes possible. At coupling energies below the threshold, the increasing magnetic field induces the following sequence of orientational transitions: homogeneous planar phase–inhomogeneous (angular) phase–homogeneous homeotropic phase–inhomogeneous angular phase. It is established that, depending on the intensity of segregation phenomena, these transitions can be of the first or second order. Analytical expressions for the fields of second-order transitions between phases are found. On an example of the optical phase difference between the ordinary and extraordinary rays of light passing through the cell of CNT suspension, it is shown that the suspension can exhibit optical bistability during the first-order orientational transition.

Adsorption Behavior of Ferromagnetic Carbon Nanotubes for Methyl Orange from Aqueous Solution.

The ferromagnetic carbon nanotubes which can be easily separated from aqueous solution were prepared and characterized by scanning electron microscope (SEM), Fourier transform infrared spectroscopy (FTIR) and X-ray diffraction (XRD). Batch experiments were carried out to investigate the adsorption behavior of ferromagnetic carbon nanotubes for removing methyl orange (MO). The results showed that these ferromagnetic carbon nanotubes were richer in surface function groups than the carbon nanotubes did, furthermore, both γ-Fe2O3 and Fe with ferromagnetism were found on the surface of carbon nanotubes. The results also demonstrated that ferromagnetic carbon nanotubes possessed stronger adsorption ability for MO than carbon nanotubes did. The adsorption isotherms followed Langmuir isotherm equation and the adsorption kinetics could be well described with the pseudo second-order kinetic model. The adsorption process involved an intraparticle diffusion, while it was not the only rate-controlling step. The values of AG were negative and the value of ΔH is -12.37 kJ/mol, proving that the adsorption of MO onto ferromagnetic carbon nanotubes was a spontaneous and exothermic process.

The Application of Carbon Nanotubes in Magnetic Fluid Hyperthermia

The aim of this paper is to present the results of the investigation into the applications of carbon nanotubes with ferromagnetic nanoparticles as nanoheaters for targeted thermal ablation of cancer cells. Relevant nanoparticles’ characteristics were exploited in terms of their functionality for biomedical applications and their magnetic properties were examined to determine heat generation efficiency induced by the exposure of the particles to an alternating magnetic field. The influence of the electromagnetic field on the human body tissues was assessed, providing quantitative measures of the interaction. The behavior of a liquid containing magnetic particles, during the exposure to the alternating magnetic field, was verified. As for the application for the ferromagnetic carbon nanotubes, the authors investigated temperature distribution in human liver tumor together with Arrhenius tissue damage model and the thermal dose concept.

Magnetic sensitivity of a dispersion of aggregated ferromagnetic carbon nanotubes in liquid crystals

Using carbon nanotubes filled with α-Fe, we have shown that aggregated ferronematic colloids demonstrate reliable and very effective response to a weak (<5 mT) magnetic field. The magnetic field realigns the aggregates of the particles which results in a non-threshold reorientation of the LC nearby, leading to the optically observed director distortions. The distortion regions expand with the increase of the magnetic field and achieve maximum size of several micrometres, comparable with the size of the agglomerates. In the non-distorted regions the reorientation of the director begins at the magnetic field reaching the Freedericksz transition value. Taking into account the extreme sensitivity of aggregated ferronematics to magnetic field, the following experimental and theoretical studies of the individual response of the aggregated nanoparticles to magnetic field may became the topical task of the physics and applications of ferronematics.