Formation Of Chain-like Clusters Research Articles

Attachment characteristics of charged magnetic cubic particles to two parallel electrodes (3D Monte Carlo simulations)

ABSTRACT The cubic particles magnetised along a diagonal direction are negatively charged and confined between two parallel electrode walls. These particles have a tendency to migrate toward and attach to the positive electrode together with the formation of chain-like clusters. We here have focused on three cases of external magnetic field direction. In the case of an external magnetic field applied in the oblique direction to the electrode wall, almost all the constituent particles of the chain-like clusters attach to the positive electrode wall in a face-to-face contact manner. In the case of an external magnetic field applied along the surface of the electrode wall, the chain-like clusters are formed in the space of the two parallel walls. In the case of an external magnetic field applied normal to the electrode wall, the tendency for the particles to form chain-like clusters along the electrode wall is the weaker among the three field directions. In this situation, the cubic particles attach to the wall surface with a vertex of the cube contacting with the surface, and from the anchored particle, a chain-like cluster is formed in the space between the two parallel walls.

Thermal conduction anisotropy of a magnetic functional fluids utilizing cluster formation of dispersed fine particles (in the case of micron-sized graphite particles)

The thermal conductivity of a magnetic fluid is expected to enhance by adding micron-sized particles with high thermal conductivity. The thermal conductivity of the magnetic fluid containing micron-sized graphite particles was investigated experimentally. The shapes of the graphite particles were sphere and flake-like. As the results of visualization experiments using the dark field microscope, the spherical graphite particles form chain-like clusters under applied magnetic field, while the fibrous structure is formed by the flake-like graphite particles, however, chain-like cluster formation cannot be clearly observed. The experiments using the transient hot-wire method showed that the thermal conductivity of magnetic fluid containing graphite particles is enhanced by applying magnetic field and by increasing the volume fraction of graphite particles.

Structural, Magnetic and Rheological Behavior of Mn–Zn Ferrofluid

Oleic acid coated Mn–Zn ferrite nanoparticles with different compositions have been synthesized by a chemical co-precipitation method to prepare kerosene based ferrofluid. XRD confirms the synthesis of single crystalline phase of Mn–Zn ferrite nanoparticles. The saturation magnetization increases with increase in zinc concentration, reaches maximum at x = 0.4 and decreases for further increase in zinc concentration. The variation in saturation magnetization can be correlated to the modifications in cation distribution as a result of replacement of Mn-ion by Zn-ion thereby modifying the superexchange interaction between the A and B sublattices. The synthesized ferrofluids behaved as Newtonian fluids in the absence of the magnetic field, which naturally reflected the lack of large aggregates. However, under the magnetic field, viscosity increased because of formation of chain-like clusters of nanoparticles showing non-Newtonian behavior of the fluid. The viscosity increases with increase in zinc concentration, reaches maximum at x = 0.4 and decreases for further increase in zinc concentration. The variation in viscosity can be correlated to the modifications in saturation magnetization as a result of substitution of Zn.

Influence of the Magnetic Interaction among Particles on Distributions of Magnetic Fluids Using Computer Simulations

Magnetic fluid is a stable colloidal dispersion of ferromagnetic particles in a liquid carrier. Once a magnetic field is applied to magnetic fluids (MF), various structures of MF are formed. A detailed understanding of structures and particle distributions in gradient magnetic fields is much important. But very few works have been done on this. In the present study, the effects of magnetic field gradient and magnetic interaction among magnetic particles on the structures of MF are investigated using a two-dimensional Monte Carlo simulation. The results show that a gradient distribution of magnetic particles is formed under gradient magnetic fields. However, as the interaction between magnetic particles increases, the distribution gradient decreases, accompanied by the formation of chain-like clusters. Moreover, with increasing the magnetic interaction, particle distribution changes from grass-like clusters to needle-like ones.

Rheology of a ferrofluid based on nanodisc cobalt particles

Rheological investigations as well as theoretical studies on ferrofluids have shown strong field and shear dependent changes in viscosity, which are correlated with the formation of chain-like clusters of magnetic nanoparticles. Moreover, the formation of these clusters leads to the appearance of viscoelastic effects or other non-Newtonian features in ferrofluids in the presence of a magnetic field. Previous investigations were carried out with differently composed ferrofluids, all of them containing particles of nearly spherical shape, but differing in the size of the nanoparticles, the volume concentration and the magnetic material. In the work presented here a ferrofluid with non-spherical cobalt nanoparticles is used, to get more information about the influence of the shape of the nanoparticles on their interparticle interaction and the resulting rheological behaviour of the suspension. For the experiments an especially designed stress controlled rheometer has been used. Experiments on yield stress as well as measurements of the magnetoviscous effect have been performed for this ferrofluid with nanodisc particles for different magnetic field strengths. The results from the yield stress experiments have been compared with those achieved for a cobalt-based ferrofluid containing spherical nanoparticles.

Relation of Viscosity and Inner Structure of Suspension under Magnetic Field

When an external magnetic field was applied on the suspension composed of ferromagnetic Ni and nonmagnetic ZrO_2 particles,the viscosity of the suspension increased drastically.The relation of viscosity and inner structure of suspension was investigated by using magnetic coils,rotational vis- cometer and optical microscope.The results show that the viscosity increases with the magnetic field strength and Ni content increasing because of the formation of chain-like clusters in the suspension. As the magnetic field increases,Ni clusters become larger,which hinders the free move of particles,so the viscosity increases.Similarly,Ni clusters in the suspension increase with Ni content increasing,and hence the viscosity increases.

PROPERTIES OF ULTRASONIC PROPAGATION IN FUNCTIONAL FLUIDS UNDER MAGNETIC FIELDS

The properties of ultrasonic propagation velocity in water-based and kerosene-based magnetic fluids and an MR fluid are examined experimentally. The ultrasonic frequency used is 1 MHz and the measurement scheme is based on the pulse method. The external magnetic field intensity is varied from 0 mT to 550 mT and is swept at a constant rate dB/dt (sweep rate). The ultrasonic propagation velocity changes with applied magnetic field and hysteresis is observed. The properties of ultrasonic propagation seem to be highly influenced by the formation of chain-like clusters (in the magnetic fluids) and robust clusters (in the MR fluid).

2302 印加磁場による磁性流体,MR流体中の超音波伝播速度への影響(S42-1 複雑流体の流動現象(1),S42 複雑流体の流動現象)

The properties of ultrasonic propagation velocity in water-based and kerosene-based magnetic fluids and an MR fluid are examined experimentally. The ultrasonic measurement scheme is based on the pulse method. The external magnetic field intensity is varied from 0mT to 550mT and the angle between the magnetic field direction and the direction of ultrasonic wave propagation is adjusted from 0°to 90°. The ultrasonic propagation velocity changes with the elapsed time of external magnetic field application and with magnetic field intensity. Moreover, the ultrasonic propagation velocity in MR fluid is larger than that in magnetic fluids. These properties of ultrasonic propagation seem to be highly influenced by the formation of chain-like clusters (in the magnetic fluids) and robust clusters (in the MR fluid).

Effect of External Magnetic Field on Ultrasonic Propagation Velocity in Magnetic Fluids

Experimental results for the properties of ultrasonic propagation velocity in kerosene-based and water-based magnetic fluids are reported. Ultrasonic wave frequencies of 1 MHz, 2 MHz and 4 MHz are used and the measurement scheme is based on the pulse method. The external magnetic field intensity is varied from 0 mT to 550 mT and the angle between the magnetic field direction and the direction of ultrasonic wave propagation is varied from 0° to 90°. The ultrasonic propagation velocity in magnetic fluids is dependent on temperature, elapsed time of applying the magnetic field, and magnetic field intensity. Hysteresis and anisotropy of ultrasonic propagation velocity are observed. These interesting results seem to be related to chain-like cluster formation in the magnetic fluids and the characteristic period of Brownian motion of the magnetic particles.

Thermal behavior and cluster formation of ferromagnetic particles in magnetic fluids

Thermal behavior and cluster formation of ferromagnetic particles in the water-based, kerosene-based and alkylnaphthalene-based magnetic fluids were investigated using an optical microscope system. Real-time visualization of the Brownian motion and the chain-like cluster formation of three types of particles were carried out under a magnetic field. The influence of the magnetic field intensity and the temperature variation on cluster formation of ferromagnetic particles was investigated.

Behavior of micromagnetic particles in an opposed-poles orientation magnetic field

Uniform microparticles with a dimension of about 1 μm in diameter and several microns in length, were obtained by an electroless deposition technique of CoNiP on bacilli initiated by molecular palladium catalysts. Water-based magnetic fluid containing the small particles was treated with magnetic fields in order to obtain regular arrays of aligned particles. Using an optical microscope with camera system, real time visualization of the magnetic particles was carried out. Both array and chain-like cluster formation of particles under magnetic field were observed. The interaction with the magnetic fields was also analyzed.

Stokesian Dynamics Simulations of Ferromagnetic Colloidal Dispersions Subjected to a Sinusoidal Shear Flow

We have conducted Stokesian dynamics simulations to investigate the dynamic properties of ferromagnetic colloidal dispersions subjected to a sinusoidal shear flow. Thick chain-like cluster formation is significantly influenced by an oscillatory shear flow even if the amplitude is relatively small, since the internal structures of thick chain-like clusters are highly sensitive to the change in the direction of the shear flow. The motion of thick chain-like clusters is out of phase to a sinusoidal shear rate, and the phase difference is strongly correlated with that of the viscosity and normal stress coefficients. The viscoelastic properties become more apparent with decreasing frequency of the oscillatory shear flow, since such properties have a strong relationship with the thick chain-like cluster formation. In other words, since thick chain-like clusters are more stable for the case of a smaller frequency shear flow, such stable clusters induce significant viscoelastic properties of ferromagnetic colloidal dispersions in a strong, applied magnetic field.

Stokesian Dynamics Simulations of Ferromagnetic Colloidal Dispersions in a Sinusoidal Shear Flow. Non-Newtonian Viscosities and Viscoelastic Properties.

We have conducted Stokesian dynamics simulations to investigate the dynamic properties of ferromagnetic colloidal dispersions subjected to a sinusoidal shear flow. Thick chainlike cluster formation is significantly influenced by an oscillatory shear flow even if the amplitude is relatively small, since the internal structures of thick chainlike clusters are highly sensitive to the change in the direction of the shear flow. The motions of thick chainlike clusters are out of phase to a sinusoidal shear rate, and this phase difference is strongly correlated with that of the viscosity and normal stress coefficients. The viscoelastic properties become more apparent with decreasing frequency of the oscillatory shear flow, since such properties have a strong relationship with thick chainlike cluster formation. In other words, since thick chainlike clusters are more stable for the case of a smaller frequency shear flow, such stable clusters induce significant viscoelastic properties of ferromagnetic colloidal dispersions in a strong applied magnetic field.

Three Dimensional Monte Carlo Simulations of Thick Chainlike Clusters Composed of Ferromagnetic Fine Particles

Three-dimensional Monte Carlo simulations have been carried out in order to investigate the thick chainlike cluster formation of ferromagnetic fine particles in an applied magnetic field. The results of the aggregate structures are summarized as follows. If a magnetic field is sufficiently strong and magnetic particle–particle interactions are relatively strong, thick chainlike clusters are formed along a field direction. The thick chainlike clusters obtained by the simulations agree well with those observed experimentally. For the increased particle–particle interactions, high potential barriers arise between thin chainlike clusters, so that it is impossible for the thin chainlike clusters to aggregate to form thick chainlike clusters. In small magnetic fields, thick chainlike clusters are not observed, since nonlinear clusters are preferred to linear clusters in this situation, whereby strong attractive forces do not act between clusters, due to flux closure.

Three Dimensional Monte Carlo Simulations of Thick Chainlike Clusters Composed of Ferromagnetic Fine Particles.

Three-dimensional Monte Carlo simulations have been carried out in order to investigate the thick chainlike cluster formation of ferromagnetic fine particles in an applied magnetic field. The results of the aggregate structures are summarized as follows. If a magnetic field is sufficiently strong and magnetic particle-particle interactions are relatively strong, thick chainlike clusters are formed along a field direction. The thick chainlike clusters obtained by the simulations agree well with those observed experimentally. For the increased particle-particle interactions, high potential barriers arise between thin chainlike clusters, so that it is impossible for the thin chainlike clusters to aggregate to form thick chainlike clusters. In small magnetic fields, thick chainlike clusters are not observed, since looplike clusters are preferred to linear clusters in this situation, whereby strong attractive forces do not act between clusters, due to flux closure.

Magneto-optical absorption in infrared region for magnetic fluid thin film

The magnetic field and wavelength dependences of the optical absorption coefficient, alpha , were measured in the infrared range for magnetic fluids containing Fe/sub 3/O/sub 4/ or MnZn ferrite particles. The absorption in the absence of magnetic fields is due mainly to the magnetic particles themselves. With increasing applied magnetic field, Delta alpha decreases for the ordinary ray and increases for the extraordinary ray. This magnetic field dependence is attributed to the formation of chainlike clusters of a few colloidal particles (microclusters) whose length is much shorter than the wavelength of the infrared ray. In the Mn-Zn ferrite magnetic fluid, Delta alpha for the ordinary and extraordinary rays increases gradually after a magnetic field is applied. The time dependence is caused presumably by growth into macroclusters whose length is comparable with the wavelength.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>