Particles In Magnetic Fluids Research Articles

Influence of large size magnetic particles on the magneto-viscous properties of ferrofluid

We compare the magneto-viscous behavior in a shear flow of three different types of magnetic suspension in the presence of a magnetic field. The first suspension contains magnetite particles of average size 10 nm dispersed in transformer oil. The second one is made of large sized magnetite particles having 30 nm particle size dispersed in transformer oil. The third suspension is a mixture of the first and second fluids in different weight proportions. The size and size distribution have been confirmed by transmission microscopy and small angle neutron scattering experiments. The rheological properties of the first two suspensions were measured for varying shear and field values. The flow behavior of the nanosized dispersed ferrofluid is described with Bingham’s yield stress model and it varied from 2.2 to 5.5 Pa on increasing the field from 0 to 1 T. The large sized particle dispersed fluid exhibits magneto-viscous behavior with increasing field. The value of Bingham’s yield stress obtained is nearly 15 times higher than that of the small size dispersion. On mixing these two fluids with different weight fractions, the Bingham yield stress value increases by a factor of three compared with that of the large sized particle dispersed fluid. The Mason number provides a good scaling of data in the steady simple flow regime. The observed yielding behavior is due to the formation of a longer chain structure in the system under the field and in-field microscopy confirms the same. The present study shows that the addition of large sized magnetic particles in magnetic fluid increases the yield stress as well as the fluid stability under a field.

The Out-Rotator of Spin Traveling Wave Pump on Magnetic Fluid

According to researching the spin traveling wave pump, the relationship of the characteristics of magnetic fluid and the press is investigated under the spin magnetic field by the theory method. The relationship of moving, magnetic field and press is investigated by the decoupled computation between the magnetic field and force. The method is scientificity and rationality by the testing. The distributing shape of magnetic fluid in the pump is affected by the adding magnetic field under the spin magnetic field when the magnetic fluid is filled in the pump. At the same time, the adding magnetic field is affected by magnetic particles of magnetic fluid. The magnetic fluid can be moved by the effect of the adding magnetic field in the pump. The flux of magnetic fluid increases with the magnetic field.

Simulation of Magnetic Fluid to Develop the Magnetic Chromatography for Magnetic Particle Separation

A magnetic chromatography is a very useful system for an ion and/or fine magnetic particle separation. Recently, its performance has been enhanced using a superconducting magnet. The superconducting magnet can generate a high magnetic field and its strong magnetic field gradients in a very small flow channel. We have developed the magnetic chromatography system to separate the fine particles. However, its numerical simulation is difficult, since the scale of the fine magnetic particles in fluid is much different from the scale of the superconducting magnet generating the strong magnetic field. In order to accurately simulate the magnetic separation, it is necessary to develop the simulation code dealing with the multiscale. The performance of the developed magnetic chromatography is evaluated by the developed simulation tool, and it is clarified that it is unsuitable for magnetic particle separation. Therefore, a magnetic chromatography is newly designed and its performance is evaluated by the developed simulation tool.

Viscous Force Model Analysis of Magnetic Viscous Effect in Magnetic Fluid

From the perspective of microscopic mechanism to study the origin and the macroscopic behavior of the magnetic viscosity characteristics need to discuss the magnetic viscosity effects of the magnetic fluid dynamics, and the magnetic viscous forces in the magnetic fluid dynamics equations is the root cause of the magnetic viscosity effects. In the paper, the common expressions of first-order viscous force and quatratic viscous force of the magnetic fluid are derived from combining the magnetic fluid viscosity expression forms under different concentrations together, while based on the molecular circulation theory and electromagnetic dynamics principle, the quatratic magnetic viscous force model of magnetic fluid is derived from the basic relationship between the magnetic relaxation process. Furthermore the coefficient correction model of the quatratic viscous force is given when the solid particles of magnetic fluid present the formation of chain. Finally it shows the magnetic fluid viscous force model and a clear description of the external magnetic field influence on the magnetic fluid viscosity changes.

ON SOME FUČÍK TYPE PROBLEM WITH CUBIC NONLINEARITY ADI APPROACH TO THE PARTICLE DIFFUSION PROBLEM IN MAGNETIC FLUIDS

The present study is devoted to the development of an ADI approach to simulate two-dimensional time-dependent diffusion process of ferromagnetic particles in magnetic fluids. Specific features of the problem are the Neumann boundary conditions. We construct an ADI scheme of formally second order accuracy approximation in time and space. It is proved that the scheme is absolutely stable and it has the accuracy in the energy norm of the second order in time and the order 3/2 in space. The numerical results of a test problem indicate that the convergence rate in space is of the second order as well.

Numerical Analysis of the Polishing Process of Inner Tube Wall Using Micron-Size Particles in Magnetic Fluids

Distribution and behaviour of micron-size magnetic particles and nonmagnetic particles in magnetic fluids in the polishing process of inner wall of small tube is investigated numerically by using the particle method based on the simplified Stokes dynamics. In this study, it is shown that chain-like clusters of both magnetic particles and those of nonmagnetic abrasive particles are formed between the two magnetic poles. The clusters are strongly held during the polishing process. The clusters of the nonmagnetic abrasive particles are surrounding the clusters of magnetic particles and they are combined with each other.

Distribution of micrometer-size particles in magnetic fluids in the presence of steady uniform magnetic field

In this paper, distribution of suspended micrometer-size particles in magnetic fluids is investigated. Microstructure formation of particles in magnetic fluids is simulated by using the discrete particle method based on the simplified Stokes dynamics. Not only magnetic particles but also nonmagnetic particles are rearranged in the field direction and form chain-like clusters due to the apparent magnetization in magnetic fluids in the presence of magnetic field. When the diameter of nonmagnetic particles is smaller than that of magnetic particles, nonmagnetic particles move into the empty space of microstructure of magnetic particles, and they are rearranged in the field direction. Uniformity of distribution of particles on the plane perpendicular to the field direction is maintained even after microstructure formation.

Magnetophoresis and diffusion of colloidal particles in a thin layer of magnetic fluids

Experimental and theoretical studies were carried out to investigate the spatial distribution of colloidal particles in magnetic fluids formed under the influence of magnetophoresis and gradient diffusion in a strong magnetic field. Several theoretical models, describing the equilibrium concentration profiles for rigid chain-like and quasispherical aggregates, are discussed. The experiment was made for four samples of magnetic fluids, differing in the average diameter of magnetic particles and the width of the particle size distribution. The analysis of the experimental data shows that the aggregates essentially change the concentration profile, making it nonlinear even in small (2 mm) magnetic fluid samples. Good agreement between the experimental and theoretical curves is observed in the case when the aggregates contain on the average 40–50 particles. The average diameter of single particles, calculated from the concentration profile curves, coincides with the average diameter, found from the magnetogranulometric analysis.

Centrifugation of dilute ferrofluids

The influence of gradient gravity field on the distribution of colloid particles in magnetic fluid placed in a long narrow cylinder is explored experimentally. The dependence of the initial magnetic susceptibility on the layer depth is measured for different times of exposure to the gradient field. The average diameter of an aggregate is estimated using the obtained results.

Dynamics of magnetophoresis in dilute magnetic fluids

Experimental and theoretical studies were carried out to investigate the spatial distribution of colloidal particles in magnetic fluids formed under the influence of magnetophoresis and gradient diffusion in strong magnetic fields. The analysis of experimental data shows that aggregates essentially change the concentration profile, making it nonlinear even in small (2 mm) magnetic fluid samples. Theoretical models, describing concentration profiles, are discussed. Good agreement between experimental and theoretical curves is observed in the case when aggregates contain on average 40–50 particles.

Structuralization of Magnetic Nanoparticles Induced by Laser Heating in Magnetic Fluids

The structuralization of magnetic particles in magnetic fluids due to the thermodiffusion induced by laser light illumination was experimentally observed in two types of magnetic fluids: one based on a mineral oil with magnetite particles covered by a monolayer of oleic acid as a surfactant and the other a kerosene-based magnetic fluid sterically stabilized by a double layer consisting of oleic acid and dodecylbenzenesulphonic acid (DBS). Forced Rayleigh scattering (FRS) showed different behaviors of magnetic particle structuralization in the observed magnetic fluids. While for the case of mineral oil-based magnetic fluids, there was observed a positive thermodiffusion (S > 0), an indication of negative thermodiffusion (S < 0) was observed in magnetic fluids based on kerosene. This was also confirmed by the time-dependent decay of a grating of magnetic particles. Numerical simulation of aggregation for the case of negative thermodiffusion was confirmed by the observed aggregation after laser illumination in kerosene-based magnetic fluids and enabled an estimated value of the negative Soret constant in the magnetic fluid studied (S ≈ −10−2 K−1).

Investigation on configuration of self-assembly in magnetic fluid film under a magnetic field

We experimentally study transmittances of water-based magnetic fluid (MF) film and the behaviors of nanoparticles under an external magnetic field. The transmittances of two orthogonally polarized rays exhibit different curve shapes. The experimental data are used to determine the values of three important parameters that are related to the intensity of the field. Based on the relationship between these parameters and the field, the self-assembly of particles is discussed. The method introduced in this paper can be employed as an available means to inspect the behavior of the particles in MF.

Contrast Variation in Small-Angle Neutron Scattering from Magnetic Fluids Stabilized by Different Mono-Carboxylic Acids

Contrast variation method in small-angle neutron scattering (non-polarized neutrons) is applied to magnetic fluids (MFs) with magnetite dispersed in benzene and coated with myristic or oleic acid in zero external magnetic field. The basic functions approach for polydisperse superparamagnetic systems is used to get structure parameters of particles in MFs.

On direct and reverse magnetically operated acoustic effect in nanocomposites

A model description of the direct and reverse acoustomagnetic effect (AME) in nanocrystaline composites produced by solidification of magnetic fluid (MF) is performed, in particular, the frequency, orientation and field dependences of the speed-induced generator voltage in the conducting circuit in the acoustic field and the elastic wave amplitudes generated in the waves in a variable magnetic field in the accompanying constant magnetic fields are addressed. Their values can be derived by setting the distribution function of the easy axes of MF particles, which in turn is controlled by the MF solidification temperature and the “freezing” magnetic field. This provides for nanocomposites with predetermined parameters of the direct and reverse AME.

Protein-stabilized magnetic fluids

The adsorption of bovine serum albumin (BSA) and egg yolk phosvitin on magnetic fluid particles was investigated. Incubation mixtures were prepared by mixing an alkaline suspension of tetramethylammonium-coated magnetite cores with protein solutions at various protein/Fe 3O 4 ratios, followed by dialysis against a 5 mM TES buffer (pH 7.0), after which separation of bound and non-bound protein by high-gradient magnetophoresis was executed. Both the kinetic profiles as well as the isotherms of adsorption strongly differed for both proteins. In case of the spherical BSA, initially, abundant adsorption occurred, then it decreased and—at high protein concentrations—it slowly raised again. In contrast, with the highly phosphorylated phosvitin, binding slowly started and the extent of protein adsorption remained unchanged both as a function of time and phosvitin concentration. Competition binding studies, using binary protein mixtures composed of equal weight amounts of BSA and phosvitin, showed that binding of the latter protein is ‘unrealistically’ high. Based on the geometry of the two proteins, putative pictures on their orientation on the particle's surface in the various experimental conditions were deduced.

Magnetic resonance of magnetic fluid and magnetoliposome preparations

In this study, magnetic resonance was used to investigate lauric acid-coated magnetite-based magnetic fluid particles and particles which are surrounded by a double layer of phospholipid molecules (magnetoliposomes). The data reveal the presence of monomers and dimers in both samples. Whereas evidence for a thermally induced disruption of dimers is found in the magnetic fluid, apparently, the bilayer phospholipid envelop prevents the dissociation in the magnetoliposome samples.

Low-temperature susceptibility of concentrated magnetic fluids.

The initial susceptibility of concentrated magnetic fluids (ferrocolloids) has been experimentally investigated at low temperatures. The results obtained indicate that the interparticle dipole-dipole interactions can increase the susceptibility by several times as compared to the Langevin value. It is shown that good agreement between recent theoretical models and experimental observations can be achieved by introducing a correction for coefficients in the series expansion of susceptibility in powers of density and aggregation parameter. A modified equation for equilibrium susceptibility is offered to sum over corrections made by Kalikmanov (Statistical Physics of Fluids, Springer-Verlag, Berlin, 2001) and by B. Huke and M. Lucke (Phys. Rev. E 67, 051403, 2003). The equation gives good quantitative agreement with the experimental data in the wide range of temperature and magnetic particles concentration. It has been found that in some cases the magnetic fluid solidification occurs at temperature several tens of kelvins higher than the crystallization temperature of the carrier liquid. The solidification temperature of magnetic fluids is independent of particle concentration (i.e., magneto-dipole interparticle interactions) and dependent on the surfactant type and carrier liquid. This finding allows us to suggest that molecular interactions and generation of some large-scale structure from colloidal particles in magnetic fluids are responsible for magnetic fluid solidification. If the magnetic fluid contains the particles with the Brownian relaxation mechanism of the magnetic moment, the solidification manifests itself as the peak on the "susceptibility-temperature" curve. This fact proves the dynamic nature of the observed peak: it arises from blocking the Brownian mechanism of the magnetization relaxation.

Real-time observation of Brownian motion and cluster movement of ferro- and non-magnetic particles in magnetic fluids

Cluster movements of ferro- and non-magnetic particles in magnetic fluids were investigated using optical microscope system and image processing system. Real-time visualizations of the Brownian motion of particles and the chain-like cluster movement of both types of particle were performed under a magnetic field. The principal objectives of this study were to clarify the applicability of the optical microscope system and image processing system, and to analyze the growth process of the cluster under magnetic field. The analysis of particle image was done using Particle Tracking Velocimetry (PTV). The results clarified that the real-time observation of Brownian motion and cluster movement of ferro- and non-magnetic particles in magnetic fluids can be carried out using the optical microscope system and the PTV image measurement. Independent continuous measurements with changing positions and velocity of the minute particle were made possible. The study concluded that the system can obtain satisfactory results on growth process measurement of cluster under a magnetic field.

The Study of Kinetic Colloidal Particles in Magnetic Fluids using Diffraction Effect on an Optical Grating Created by Intersecting Laser Beams

In this paper a short characteristic of magnetic fluids and some of their applications are presented a simple one-dimensional model of creation of thermal and absorption grating is explained. The method of generation of optical grating by using the interference two intersecting coherent laser beams is presented. In conclusion some possibilities of utilisation optical created grating are also indicated.

Incrusting structure of nanosized Fe3O4 particles in magnetic fluids

High-performance nanosized Fe3O4 magnetic fluids are prepared by chemical co-precipitate method. The microstructure of magnetic fluids is characterized using a transmission electron microscope (TEM) and high-resolution microscope (HREM). The results are satisfactory. The nanosized magnetic particles have diameter of 8–10 nm and the minimum diameter is 4 nm, belonging to super-paramagnetic material. The nanosized magnetic particles crystallized completely and have clear crystal boundary. The surfactant used in the test coats the magnetic particles homogeneously and forms a uniform and complete elastic spherical shell of amorphous phase around the magnetic particles. The study proves that the incrusting layer of surfactant has the protective effect and stable effect on the magnetic particles. These effects can enhance and maintain the magnetic properties of the magnetic fluids effectively.