Concentrated Magnetic Fluids Research Articles

Optimization of the coating process in the PEGylated chitosan-based doped cobalt ferrite nanoparticles for hyperthermia applications using the Taguchi method

In this study, the parameters of coating process in the PEGylated chitosan-based doped cobalt ferrite nanoparticles for hyperthermia applications was optimized using the Taguchi method. The effect of chitosan and polyethylene glycol as well as the glutaraldehyde (crosslinker) contents on the structural, microstructural, and magnetic properties and the colloidal stability of the nanoparticles were investigated. Ultimately, to optimize the properties of the nanoparticles, the Taguchi method (L16 orthogonal array) was employed. The incorporation of the Ca2+ and Gd3+ into the spinel structure with an average crystallite size of 21 nm was successfully verified by X-ray diffraction (XRD) and the Rietveld refinement analysis. Moreover, thermogravimetric (TGA) analysis and Fourier-transform infrared spectroscopy (FT-IR) demonstrated the effective functionalization of the chitosan and polyethylene glycol coatings. Vibrating sample magnetometer (VSM) measurements revealed that saturation magnetization (Ms) was achieved in the range of 54.91–60.42 emu/g. Also, microstructural observations indicated that the coating layer can affect the particle size distribution and morphology. The Taguchi method identified that the glutaraldehyde content is the most expressive parameter influencing the nanoparticles’ properties, with the optimum properties achieved at chitosan, polyethylene glycol, and glutaraldehyde of 0.4 g, 0.08 g, and 1.2 ml, respectively. The antibacterial analysis confirmed the promising potential of the coated nanoparticles for biomedical applications. Furthermore, the magnetic heating efficiency of the synthesized nanoparticles was investigated in various concentrations of magnetic fluid, demonstrating their suitability for magnetic hyperthermia application.

Particle correlations in concentrated aqueous ferrofluids upon dilution by small-angle X-ray scattering

Small-angle X-ray scattering is applied to study particle correlations in concentrated (up to 7.5 vol% magnetite) aqueous magnetic fluids with double-layer coating by either oleic or lauric acids. The structure of aggregates in these fluids is analyzed when diluting samples with the goal of finding out a concentration threshold at which the aggregates can be considered weakly interacting independent formations. For dilute systems, suitable models fitting experimental scattering curves are proposed, which take into account the polydispersity of both particles and aggregates. It is shown that particle correlations found in aggregates are dependent on the surfactant coating.

Preparation of water-based dextran-coated Fe3O4 magnetic fluid for magnetic hyperthermia

Abstract Fe3O4 nanoparticles were prepared by chemical co-precipitation, modified with dextran, and dispersed in water to form a magnetic fluid (MF) for use in biomedical areas. The analyses of stability and magnetic property demonstrate that the prepared functional MF possesses outstanding stability (stability index within 60 days, high dilution stability, and autoclaved stability) and high magnetization (the values χ and M s of MF are 5.87 × 10−4 and 20.57 emu/g, respectively). Due to the coating of dextran, the toxicity of MF is minimal (in vitro survival rate of MCF-7 cells, blood compatibility, and in vivo toxicity). In addition, although the outer layer is coated with dextran, the M s intensity remains high, so the Fe3O4 MF owns a fast magnetic temperature response (when the MF concentration is 55 mg/mL, it can rapidly rise to 55°C within 800 s), which plays an extremely vital role in MF hyperthermia. So, the MF can effectively cause necrosis of human lung A549 cells, which shows a certain application potential.

Temperature‐Sensitive Properties and Mechanism of Smart Magnetic Fluids Modified with Cellulose Derivatives

AbstractCombining magnetic materials with environmentally sensitive polymers to develop intelligent magnetic fluids that respond to external stimuli has become a new research hotspot. At present, the bottlenecks in the development of temperature‐sensitive materials are the complex composition, and its properties in different laboratories vary greatly. Moreover, despite extensive research on magnetic fluids, there remains a dearth of systematic investigation into temperature‐sensitive intelligent magnetic fluids. In this study, we utilized a UV‐visible spectrophotometer to measure the change in transmittance of different magnetic fluid solutions with temperature variation. We systematically investigated the effects of the magnetic fluid dispersion medium, size and concentration of magnetic nanoparticles, type and viscosity of cellulose on the temperature sensitivity of the magnetic fluid. We found that compared with Hydroxypropyl Methyl Cellulose (HPMC) (type I), HPMC (type II) modified magnetic fluid has better stability and a higher phase transition temperature. Moreover, with the increase of the concentration of magnetic fluid, the phase transition temperature is higher. In addition, the lower the viscosity of HPMC‐modified magnetic fluid, the better the stability and the higher the phase transition temperature. We also studied the mechanism of temperature sensitivity, and the results showed that hydrogen bond interactions play an important role. This research will facilitate the use of temperature‐sensitive smart magnetic fluids for biomedical application.

Magnetic Field Sensing Using Tapered Small-Core Optical Fibre Surrounded by Different Concentrations of Magnetic Fluid.

In this paper, a high-sensitivity magnetic field sensor based on a single-mode-tapered small-core-single-mode (STSCS) optical fibre structure is investigated. The tapered small-core section of STSCS is surrounded by magnetic fluid (MF) containing ferromagnetic particles (FMPs) of different concentrations. The FMPs align themselves along the magnetic field, depending on the strength of the magnetic field. This alignment of FMPs changes the refractive index around the tapered small-core section, which in turn changes the output spectral response of the STSCS optical fibre structure. The change in spectral response is then calibrated for sensing the magnetic field strength. This paper also investigates the effect of both the taper waist diameter of the STSCS optical fibre structure and the concentration of MF surrounding it on the magnetic field sensitivity. The maximum sensitivity demonstrated in this paper is 0.46 nm/mT for a taper waist diameter of 10 μm surrounded by 1.22% FMPs in the MF. The magnetic sensor demonstrates reversible results, and its effects on the orientation of the magnetic field along the X-Y, X-Z and Y-Z axes are also investigated, which suggest that the sensor is capable of vector magnetic field measurement.

Ferrofluid high internal phase emulsion polymer foams for soft, magnetic materials

Magnetic components are an essential part of current electronics, although the materials used to make magnetic components are almost exclusively rigid and non-deformable. The high modulus and inflexible behavior of typical magnetic materials makes their integration into soft, deformable electronics challenging. Soft electronics, however, is a dynamic field pushing forward the state-of-the-art in wearable sensors, human-machine interaction, and biomimetic robots. In order to access the wide range of functionality of rigid electronics, magnetic materials must be made that are high performing and deformable. One previously unexplored route to creating such materials is the encapsulation of a high concentration of magnetic fluids, such as ferrofluids (FF), into an elastomer using high internal phase emulsification. In this work, the formulation factors required to make an effective ferrofluid high internal phase emulsion polymer foam (polyHIPE) utilizing polydimethylsiloxane (PDMS) were investigated such as the emulsifiers, polyHIPE curing kinetics, and the interaction of emulsified nanoparticles. The porous structure, magnetic properties, and mechanical properties of the final, successful FF/PDMS polyHIPE were subsequently characterized. Pores ranged between 10 and 50 μm with visible nanoparticle aggregation. FF/PDMS polyHIPE had an Ms of 18 A∙m2/kg and susceptibility of 0.69, which is reduced as compared to neat ferrofluid, as expected, but an improvement on ferrofluid polymer dispersions found in the literature. Coercivity and magnetic remanence also decreased with respect to the neat ferrofluid. Rheology demonstrated that the polyHIPE had a significantly lower modulus than the neat PDMS as well as a lower modulus than any magnetic composite material currently published. The FF/PDMS polyHIPE created in this work not only demonstrates the potential for deformable magnetic materials based on the emulsification of high concentrations of magnetic fluid into elastomers, but also the potential to create even higher performing materials using a higher concentration of magnetic fluid or ferrofluids with superior magnetic properties.

Behavior of a gas bubble separating from a cavity formed in magnetic fluid in an inhomogeneous magnetic field

In this work, we report results of the experimental study of the dynamics of a gas bubble separating from the air cavity in a magnetic fluid placed in an inhomogeneous magnetic field created by a ring magnet. Two experiments were carried out for samples with different concentrations: video recordings of the interphase boundary in a flat channel and recordings of electromagnetic vibrations caused by the gas bubble oscillations in a magnetic fluid. It is shown that the bubbles have a stable size. The respective dependencies of the bubble size on the magnetic fluid concentration and the air supply argue that it is possible to use the considered setup as a microdoser or a gas meter in microfluidics applications.

Magnetic sensor based on WGM hollow microbubble resonator filled with magnetic fluid

In this work, a magnetic sensing scheme based on whispering gallery mode (WGM) hollow microbubble resonator (HMR) filled with magnetic fluid (MF) is proposed. The HMR is made by the pressure-assisted arc discharge method on the microcapillary. WGM is excited by evanescent fields in HMR. The quality factor of resonator is 4.02×106. Then, the influence of the wall thickness of HMR and the concentration of MF on the sensor is studied both theoretically and experimentally. When MF is infiltrated in the HMR, the refractive index (RI) of the MF increases with the increase of the magnetic field intensity, resulting in the shift of the resonance wavelength. By reducing the wall thickness, the magnetic sensing sensitivity is increased from 2.6 pm/mT to 25.21 pm/mT within the magnetic field intensity range of 2 mT–20 mT. In addition, the increase in the concentration of MF and the clustering phenomenon caused by it have also been observed. This work provides a novel magnetic sensing scheme, and the proposed WGM resonator has great application prospects in optofluidic sensing.

Gyrotropy and magnetic fluid dependences of magneto-optical properties in YIG-magnetic photonic crystal fiber

In this work, a kind of magnetic photonic crystal fiber (MPCF) design based on yttrium iron garnet (YIG) structure filled with magnetic fluid (MF) is presented. In order to improve the magneto-optical (MO) properties of isolator devices, a numerical study has been developed to investigate the non-reciprocal TE-TM mode conversion. This technique consists in producing, under the influence of a magnetic field parallel to the direction of propagation, a coupling between the modes. The influence of gyrotropy and MF infiltration at different magnetic nanoparticle volume fraction concentrations is investigated. The results revealed that the mode conversion efficiency (Rm) increases with the increase of the MF concentration, while modal birefringence (∆n) is inversely proportional to its increase. Thus, the higher concentration provides the best results. For MF concentration and gyrotropy equal respectively to 1.75% and 0.0125, Rm is improved to over 93%, and ∆n is reduced to close to 10–6. Whereas, Rm decreases to 89.59 and ∆n increases to 6 × 10–6 for MF concentration equal to 0.25%. From these results, it can be seen that this MPCF filled with MF concentration equal to 1.75% is well suited to the design of MO isolators.

Air Cavity Capture by a Flat Channel with Magnetic Fluid in an Annular Magnet

The paper discusses research on visualization of air cavity capture and transportation in a flat channel filled with magnetic fluid and located along the annular magnet axis. It takes the results of the model theory of “weakly magnetic medium” based on construction of a system of isolines of magnetic field intensity module (Н = const) for the magnetic fluid filling the tube and compares them to the air cavity image produced in a thin fluid layer. Distinctive features of the stage-by-stage air cavity capture are theoretically explained for different magnetic fluid concentrations. The results can be useful in solving practical microhydraulics problems.

Structural characterization of concentrated aqueous ferrofluids

Structure characterizations of concentrated water-based magnetic fluids stabilized by oleic and lauric acids were done by means of small-angle neutron scattering (SANS) and complemented by dynamic light scattering and magnetization analysis. Stability of ferrofluids with time against sedimentation was concluded despite the presence of aggregates in solutions. Differences in the average sizes of individual polydisperse magnetite nanoparticles coated with surfactants and their aggregates were revealed. Structural parameters obtained from SANS have been confirmed by magnetogranulometry data. The comparative analysis of the aggregation and its change upon dilution is made basing on the data of SANS and dynamic light scattering techniques.

Magnetic field and temperature dual-parameter sensor based on magnetic fluid materials filled photonic crystal fiber.

A dual-parameter sensor based on a photonic crystal fiber (PCF) concatenated with a fiber Bragg grating (FBG) is proposed and experimentally demonstrated for simultaneous measurement of magnetic field and temperature. Novel magnetic fluids (MF) with different concentration and surfactant are filled in the air holes of PCF. The magnetic field measurement property is only determined by PCF, while the temperature is co-determined by PCF and FBG. Experimental results show that the wavelength shift has a good linearity corresponding with temperature and magnetic field. Temperature and magnetic field sensitivity are proportional to concentration of MF and are affected by different surfactants. For PCF point, when polyethylene glycol is used as a surfactant and the magnetic fluid concentration is equal to 0.15, the highest magnetic field sensitivity is up to 924.63 pm/mT. The proposed sensor has a high sensitivity as well as cross-sensitivity resistance, which provides a promising candidate for dual-channel filtering or multi-parameter measurement applications.

Preliminary in-vitro investigation of magnetic fluid hyperthermia in cervical cancer cells

The present study reports auto-tunable temperature sensitive iron-based magnetic nanoparticles fluid synthesized for its application in magnetic fluid hyperthermia. The effect of magnetic field and concentration of the sample is investigated for the induction heating at 350 kHz frequency. The concentration of magnetic fluid and magnetic field was optimized based on the specific absorption of the sample. The cytotoxicity of the optimized magnetic fluid was analyzed on cervical cancer cell line HeLa with and without magnetic field applicator by performing MTT assay. The cytotoxicity assay after induction heating for the magnetic fluid showed cell death up to 75% for 24 h of interaction of fluid with cells. Upon increasing the time of interaction of magnetic fluid to 36 h and for 60 min hyperthermia heating session, almost all cells were found dead. The preliminary analysis revealed significant efficacy of the synthesized magnetic fluid to caused cell death due to hyperthermia of one hour session. In future such type of magnetic fluids can be used for localized treatment of cancer under magnetic field.

Characterization of a magnetic fluid exposed to a shear flow and external magnetic field using small angle laser scattering

The paper demonstrates a possibility to use Small Angle Light Scattering (SALS) method realized in a conventional laboratory to investigate structuring processes in a magnetic fluid simultaneously exposed to a shear flow and an external magnetic field. We have used a custom made SALS-setup with a laser source combined with a microfluidic chip, an electromagnet and a magnetic circuit to obtain scattering images of a low concentrated biocompatible magnetic fluid with clustered iron oxide nanoparticles. The application of an external magnetic field drastically influences the physical behaviour of the fluid and this effect is directly related to aggregation of particles resulting in chains with a dimension of several micrometers. These chains lead to an anisotropy of the scattering patterns. We have observed an influence of the field and flow on the intensity gradient of the obtained scattering patterns. The presented method opens broad perspectives to obtain microstructural information as well to evaluate structuring kinetics of the diluted magnetic suspensions using conventional laboratory conditions. The SALS measurements are accomplished with a full characterization of the fluid using magneto-rheometry, vibrating sample magnetometry, microscopy as well as dynamic light scattering.

Spectral dependences of the complex refractive index of concentrated magnetic fluids

Spectral dependences of the complex refractive index of concentrated magnetic fluids

Complex refractive index of concentrated magnetic fluids

The spectra of the real and imaginary parts of the refractive index of magnetic fluids based on kerosene with a solids phase concentration of 1% to 35% are experimentally measured. The comparison of calculations results have been made according to Maxwell-Garnett and Bruggeman’s models of effective medium approximation. The influence of refractive index spectra on the extinction of light in magnetic fluids is shown.

Measurement of the refractive index of solutions based on digital holographic microscopy

A new approach for the refractive index (RI) measurement of solutions is proposed based on digital holographic microscopy. The experimental system consists of a modified Mach–Zehnder interferometer and related lab-developed analysis software. The high quality digital hologram of the tested solution is obtained by the real-time analysis software, which is firstly encapsulated into a capillary tube, and then the capillary tube is inserted in a matching fluid. An angular spectrum algorithm is adopted to extract the phase distribution from the hologram recorded by a CCD. Based on a capillary multi-layer calculation model, the RI of the tested solution is obtained at high accuracy. The results of transparent glycerol solution measured by the proposed method are more accurate than those measured by the Abbe refractometer. We also measure the RI of translucent magnetic fluid, which is not suitable to be measured by the Abbe refractometer. The relationship between the RI and the concentration of magnetic fluid is experimentally studied, and the results show that the RI is linearly related to the concentration of dilute magnetic fluid.

On variations in size distributions of particles and aggregates upon dilution of magnetic fluids

Variations in size distributions of particles and aggregates upon dilution of kerosene-based magnetic fluids have been studied by dynamic light scattering. The data obtained on samples of magnetic fluids produced by three different manufacturers have shown that the dilution of an initial concentrated magnetic fluid leads to the formation of a system of unstable aggregates with sizes ranging from 70−100 nm to 1 μm. The aggregates peptize for 2−4 days to result in the establishment of stationary particle and aggregate size distributions.

Evaluation of nano-magnetic fluid on malignant glioma cells.

The temperature variation rule of nano-magnetic fluid in the specific magnetic field and the effect on the treatment of malignant glioma were examined. The temperature variation of nano-magnetic fluid in the specific magnetic field was investigated by heating in vitro, and cell morphology was observed through optical microscopy and electron microscopy. MTT detection also was used to detect the effect of Fe3O4 nanometer magnetic fluid hyperthermia (MFH) on the proliferation of human U251 glioma cell line. The Fe3O4 nano MFH experiment was used to detect the inhibition rate of the tumor volume in nude mice with tumors. The results of the experiment showed that the heating ability of magnetic fluid was positively correlated with its concentration at the same intensity of the magnetic field. The results also indicated the prominent inhibitory effect of nanometer MFH on the proliferation of glioma cells, which was a dose-dependent relationship with nanometer magnetic fluid concentration. The hyperthermia experiment of nude mice with tumors displayed a significant inhibiting effect of Fe3O4 nanometer magnetic fluid in glioma volume. These results explain that iron (II, III) oxide (Fe3O4) nanometer MFH can inhibit the proliferation of U251 glioma cells, and has an obvious inhibitory effect on glioma volume, which plays a certain role in the treatment of brain glioma.

Magneto-optical properties of magnetic photonic crystal fiber of terbium gallium garnet filled with magnetic fluid

We present in this work, magneto-optical (MO) properties of a magnetophotonic crystal fiber (MPCF) based on terbium gallium garnet Tb3Ga5O12 or TGG. The air holes of a periodic triangular lattice are filled with magnetic fluid (MF). With a light which can be confined in the core area of this MF filled MPCF we obtain a confinement corresponding to the propagation of the single mode by assuming an effective index (neff). The variations of neff as a function of the gyrotropy parameter (g) and magnetic nanoparticle volume fraction concentrations are well established at the telecommunication wavelength λ=1.55μm. The TE-TM mode conversion based on the Faraday rotation and modal birefringence are then numerically simulated. Faraday rotation exhibits largest value of 8700.08°/cm at MF concentration of 0.25% and g=0.0144, whereas the modal birefringence is reduced to 0.00177 at the same conditions. These results could be helpful for experimentally designing and realizing isolators with these filled MF-MPCFs based on this TGG material. They appear to possess significant potential for the practical applications due to their unique MO properties.