Suspensions Of Magnetic Particles Research Articles

Magnetization Dynamics of a Suspension of Noninteracting Magnetic Particles in the Presence of a Static Uniform Magnetic Field

Magnetization Dynamics of a Suspension of Noninteracting Magnetic Particles in the Presence of a Static Uniform Magnetic Field

Discontinuous Shear Thickening of Suspensions of Magnetic Particles in Relation to the Polymer Coating on Their Surfaces

The phenomenon of discontinuous shear thickening (DST) is observed in suspensions of solid particles with a very high-volume fraction. It is characterized by an abrupt decrease in the shear rate for critical stress during a ramp of stress. This behavior can be reproduced in numerical simulations by introducing a local friction between two particles above a given local force. We present experimental results showing this DST behavior obtained with suspensions of magnetic (iron) and nonmagnetic (calcium carbonate) particles and different amounts of a superplasticizer molecule used in the cement industry. For both types of particles, the same behavior was observed with first an increase in critical stress with the amount of plasticizer followed by a decrease at higher concentrations but with a larger viscosity before critical stress was reached. At a low concentration of plasticizer, the low critical stress is interpreted by the local sliding of plasticizer molecules on the surface of particles. At higher concentrations, when total coverage is achieved, the critical stress is higher since it has to remove the molecules out of the surface. At still higher concentrations, the increase in viscosity is explained by the formation of multilayers of molecules on the surface of the particles. This interpretation is supported by the measurement of the adsorption isotherm of the plasticizer on the surface of the particles.

IMPACT ANALYSIS OF SURFACE ROUGHNESSOF THE PLATE-PLATE MEASURING SYSTEM ON RESISTANCETORQUE IN INTERACTION WITH MR FLUID

Magnetorheological (MR) fluids are complex suspensions of magnetic particles in a non-magnetic carrierfluid. They exhibit ‘smart’ properties that enable them to change their rheological parameters in responseto a change in the external magnetic field applied. This behavior is used in some engineering solutions, e.g.MR clutches or brakes. For such systems to work correctly, the resistance torque achieved by contact withthe MR fluid must be properly determined. This paper demonstrates how surface roughness of a contactsurface between the solid and the MR fluid affects the resistance torque value. Measurements were madeon a dedicated rotational rheometer using a shear mode fluid, most closely replicating the way MR clutchesand brakes work. Plate-plate geometry was used, in standard design, and modified by pasting sandpaper withdifferent grit levels. The tests have shown that the roughness of the mating surface affects the resistance torqueresults.

Elucidation of the trapping characteristics of magnetic disk-like particles in a Hagen-Poiseuille flow via Brownian dynamics simulations (usage of multi-magnetic poles)

In the present study, we elucidate the behaviour of a suspension composed of magnetic disk-like particles that flow in a Hagen-Poiseuille flow in a gradient magnetic field and the trapping characteristics of the magnetic particles. To this end, we utilise multiple pairs of magnetic poles located outside the cylindrical system. Brownian dynamics simulations were performed in order to clarify the dependence of these characteristics on a variety of factors. It is seen that an increase in the magnetic field strength improves the trapping characteristics of disk-like particles if the influence of an applied magnetic field is sufficiently more dominant than that of a flow field and that of the magnetic particle-particle interaction. In the case of a strong magnetic particle-particle interaction, thin chain-like clusters are formed from an anchored particle trapped around a magnetic pole. If the two poles are sufficiently close to each other, an arch-type cluster is formed between them. We expect that this arch-type cluster may give rise to good trapping performance even in the presence of a strong flow field if the formation arises at a sufficiently large separation distance between the pair of magnetic poles. Highlights We have performed Brownian dynamics simulations for a magnetic disk-like particle suspension in a Hagen-Poiseuille flow. If the magnetic particle-particle interaction is sufficiently more dominant than the flow field, thin chain-like clusters are formed from an anchored particle. As the pole separation distance decreases, an arch-type configuration tends to be formed along the surface of the wall. This arch-type cluster that is formed between the pair of magnetic poles may be expected to improve the trapping characteristics depending on the pole separation distance.

Аналитический расчет значения магнитной проницаемости суспензии магнитных частиц в немагнитной жидкости

The issues of the hyperthermia method is primarily associated with attempts to concentrate the electromagnetic field, which has a heating effect, in the area of influence using an introduced suspension of magnetic nanoparticles. These particles are concentrated using a magnetic field in the desired area and then heated by an alternating electromagnetic field, thereby heating the body tissue to provide a therapeutic effect. To determine the heating temperature and its connection with the parameters of the acting electromagnetic field, it is necessary to know the electromagnetic parameters of the heated medium, namely the body tissues and the introduced suspension of magnetic particles. First of all, it is necessary to determine such suspension parameters as effective magnetic permeability and effective conductivity. This work is devoted to the analytical solution of the problem of determining the effective magnetic permeability of a suspension of magnetic particles in a liquid.

Phase separation of a magnetic fluid: Asymptotic states and nonequilibrium kinetics.

We study self-assembly in a colloidal suspension of magnetic particles by performing comprehensive molecular dynamics simulations of the Stockmayer (SM) model, which comprises spherical particles decorated by a magnetic moment. The SM potential incorporates dipole-dipole interactions along with the usual Lennard-Jones interaction and exhibits a gas-liquid phase coexistence observed experimentally in magnetic fluids. When this system is quenched from the high-temperature homogeneous phase to the coexistence region, the nonequilibrium evolution to the condensed phase proceeds with the development of spatial as well as magnetic order. We observe density-dependent coarsening mechanisms-a diffusive growth law ℓ(t)∼t^{1/3} in the nucleation regime and hydrodynamics-driven inertial growth law ℓ(t)∼t^{2/3} in the spinodal regimes. [ℓ(t) is the average size of the condensate at time t after the quench.] While the spatial growth is governed by the expected conserved order parameter dynamics, the growth of magnetic order in the spinodal regime exhibits unexpected nonconserved dynamics. The asymptotic morphologies have density-dependent shapes which typically include the isotropic sphere and spherical bubble morphologies in the nucleation region, and the anisotropic cylinder, planar slab, cylindrical bubble morphologies in the spinodal region. The structures are robust and nonvolatile, and exhibit characteristic magnetic properties. For example, the oppositely magnetized hemispheres in the spherical morphology impart the characteristics of a Janus particle to it. The observed structures have versatile applications in catalysis, drug delivery systems, memory devices, and magnetic photonic crystals, to name a few.

Flow and Heat Transfer of Micropolar Ferrofluid at Stagnation Point on a Horizontal Flat Plate in the Presence of Magnetic Field and Thermal Radiation

Ferrofluid demonstrates Newtonian or non-Newtonian fluid behaviour depending on the characteristics of ferrofluid. Generally, ferrofluid consists of a stable colloidal suspension of single-domain magnetic particles in a base fluid that can assume non-Newtonian fluid behaviour involving a spin vector and microinertia tensor in flow motion. These two properties possess the theory of micropolar fluid which exhibits microrotational motions and spin inertia in microscopic behaviour. Therefore, this theoretical study is focused to investigate the boundary layer of micropolar ferrofluid flow and heat transfer at the stagnation point on the horizontal flat plate. Magnetite (Fe3O4) nanoparticles and water (H2O) compose in ferrofluid exposed to the magnetic field and thermal radiation is considered. The influences of ferroparticles volume fraction and micropolar parameter on the ferrofluid flow and heat transfer are evaluated mathematically. The partial differential equations have been formulated based on purposed assumptions using Tiwari and Das model and are simplified into ordinary differential equations, which are then solved numerically by Runge-Kutta Fehlberg (RFK45) method. The numerical results of the velocity profile, temperature profile, angular velocity profile, reduced skin friction and reduced Nusselt number are scrutinised in different values of ferroparticles volume fraction and micropolar parameter to estimate the ferrofluid flow and heat transfer. It is found the velocity profile of micropolar ferrofluid flow increases when elevates the ferroparticles volume fraction but decreases when increasing the micropolar parameter. Meanwhile, enlarging ferroparticles volume fraction of micropolar ferrofluid also enhances the temperature profile, reduced skin friction and reduced Nusselt number in the presence of magnetic field and thermal radiation parameter.

B-058 Development and Evaluation of the Assay for Detection of Human Specific IgE Against Animal Dander Allergens on a Fully Automated Chemiluminescence Immunoassay Platform—Autolumo® A2000 Plus

Abstract Background The detection of specific IgE is a key method for diagnosing allergic diseases. An accurate, user friendly and cost-effective way to clinically diagnosing allergies is beneficial for the patients. Our detection kit together with the Autolumo A2000 Plus chemiluminescence fully automated platform provide a new and more effective (40 minutes) way for detection of specific IgE with simple operation, high sensitivity and specificity. Methods The Animal Dander Allergen Mix Assay kit detects specific IgE against cat dander (E1), horse dander (E3), cow dander (E4) and dog dander (E5). Performance evaluation of the animal dander mix, E1, E3, E4 and E5 assay kits for the detection of specific IgE in serum was performed on our automated chemiluminescence platform (Autolumo A2000 Plus) and compared to a well-characterized platform (ImmunoCAP, Phadia). During detection, magnetic particle suspension, antigen solution, patient sample, and enzyme conjugate were added sequentially. A streptavidin-biotinylated antigen-sIgE antibody-anti-IgE-HRP conjugate complex is formed, wherein the amount of the anti-IgE-HRP conjugate is positively correlated to the amount of sIgE antibodies in the patient sample. After the substrate is added, the HRP catalyze the chemical reaction to generate a recordable signal in the form of light. The intensities of the light were obtained by using a chemiluminescence quantitative analyzer, and the standard curve was generated according to the 7-point calibration, and then the sIgE antibody concentrations in the serum sample were analyzed. The overall agreement, method comparison, precision, linearity, and stability of our mixed and single assay kits were evaluated using serum samples (n > 140) that had been characterized with Phadia. Results The overall agreement for the animal dander mix assay is 91.84%, with the average intra-run and inter-run precision to be 1.97% and 4.21% respectively. The limit of blank (LoB) and limit of detection (LoD) for the animal dander mix assay is 0.019 kU/L and 0.045 kU/L respectively. The sensitivity for our single E1, E3, E4, and E5 assays are 97%, 85.6%, 70.8%, and 80.2%, respectively. All single assays have a specificity >90%, total precision <5% CV, and a linearity with R2 > 0.999. The LoB, LoD and recommended LoQ for all single assays are 0.019 kU/L, 0.037 kU/L, and 0.1 kU/L respectively. The average signal drifts after 10 days incubation in 37C is less than 10% indicating the assays are stable. Conclusion Autolumo A2000 Plus is a fully automated chemiluminescence Immunoassay platform that provides accurate and cost-effective screening for allergy diagnostics with excellent overall agreement, precision, and stability.

Effect of interparticle correlation on magnetic hyperthermia in biological media: A numerical study

Numerical simulations of the temperature field of a circular tumour subjected to magnetic hyperthermia are presented. The calculation domain is composed by a 5 mm circular tumour surrounded by a 2 cm × 2 cm region of a healthy tissue. Realistic values of the biological media properties are considered. Simulations are carried by an in-house research code that solves the biological heat equation in the presence of a magnetic dissipation term through a finite differences scheme. The magnetic source term is expressed in terms of the out-of-phase response of the fluid’s complex susceptibility, when subjected to an oscillatory magnetic field. This quantity is obtained using asymptotic theories and numerical simulations in the scale of the magnetic nanoparticles through another in-house research code based on Langevin Dynamics. Dipolar particle interactions are computed through a robust scheme of Ewald summation. The microscopic formulation for the particles also considers Brownian effects in their translational and rotational motion. Realistic values of these parameters are considered in order to provide a dimensional evaluation of the temperature field in the biological tissue comparable to previous numerical and experimental studies. The role of particle size distribution on the temperature field is carefully investigated. Temperature fields are also linked with microscopic geometrical features of suspended magnetic particles in order to provide a clear multiscale understanding of the physics of magnetic heat induction using alternating fields. Our results indicate that the role of dipolar interactions seems to be relevant for particle radii in the range 5nm≤a≤7nm, specially for higher volume fraction of particles, where the classical Langevin model for the saturation susceptibility fails in the prediction of the steady-state tumour temperature. For a volume fraction of particles of 15% the differences on the final temperature of the tumour associated with dipolar interactions are in the order of 20% for particles with a nominal radius in the range 5nm≤a≤7nm. In dilute regimes the classical Langevin model succeeds in the prediction of the final temperature of the tumour as expected.

Investigation of quasistatic and dynamic mechanical properties of thermoplastic polyurethane magnetorheological elastomers

Thermoplastic magnetorheological elastomers (MRE) are soft magnetic materials with multi stimuli response. As the name suggests, thermoplastic MREs are formed by the suspension of magnetic particles in a thermoplastic elastomer matrix, whose rheological properties can be controlled by temperature. The composite itself can thus be controlled by temperature and magnetic field. In this article, we present the method and results of quasistatic and dynamic mechanical properties of thermoplastic polyurethane MREs (TPU-MREs) based on the observations made on the influence of hardener and plasticizer content from the composition point of view and the directional interdependence of strain and magnetic field on the magnetorheological (MR) effect. Quasistatic tensile and torsion tests followed by dynamic oscillation tests conducted within the linear elastic regime at three different temperatures with and without externally applied magnetic field are performed on the TPU-MRE samples. The tests are conducted with an inhouse developed test setup adapted to a commercial rheometer. The obtained results demonstrate a strong correlation to the change in moduli of the TPU-MRE with respect to change in composition and temperature. From the results obtained, one can conclude that samples with lower hardener content with plasticizer have the highest relative MR effect.

Macroscopic Helicity of a Suspension of Chiral Magnetic Particles Based on a Nematic Liquid Crystal

Macroscopic Helicity of a Suspension of Chiral Magnetic Particles Based on a Nematic Liquid Crystal

Macroscopic helicity of a suspension of chiral magnetic particles based on nematic liquid crystal

The basic state of a suspension of chiral ferroparticles based on a nematic liquid crystal is studied when the finite coupling between the impurity and liquid crystal subsystems is considered. An additional contribution to the free energy functional due to the chiral shape of impurity particles, which describes the formation of spontaneous macroscopic helicity of the orientational structure of a nematic liquid crystal, is proposed.

Rheometric and stability analysis of additive infused magnetorheological fluids: a comparative study.

Magnetorheological fluid (MRF) is a smart responsive fluid, when exposed to the magnetic field, reflects a noticeable transformation in fluid viscosity due to the presence of field responsive particles in the fluid. MRF has been utilized in variety of applications, which despite possess significant concerns regarding on sedimentation due to the density mismatch between the carrier fluid and the suspended magnetic particles. To improve the resistance of rapid sedimentation, this research aims to incorporate one of the component (additive/surfactants) blended into the fluid. The objective of the study focuses to determine the efficient incorporate-infused fluid for further application and sedimentation resistance. In this study, MRF is infused with siloxane, lithium, oleic acid and SDBS (Sodium Dodecyl Benzene Sulfonate) as additive and surfactants along with silicon oil as a carrier fluid. The significant repercussion parameters such as rheology behavior of the samples, temperature and particle sedimentation has been examined and interpreted. Substantially, the effective sample and performance has been comprehended with the insightful comparative results obtained.

Synergistic interactions of binary suspensions of magnetic anisotropic particles.

We report the effect of the dipole-dipole interaction and shape anisotropy in suspensions of permanently magnetized anisotropic particles. We quantify the dipolar interaction energy using an ellipsoid-dipole model to describe particles with similar or dissimilar shapes. The expression captures the physics of the point-dipole interaction energy between uniformly magnetized spherical particles. Additionally, we report Monte Carlo simulations to describe the effect of dipolar interaction and shape anisotropy under different field strengths. Results show that the shape anisotropy and dipolar interactions modify the head-to-tail interaction with respect to spheres, promoting dendritic and barbed-wire structures in uniform ellipsoids and binary mixtures, respectively. Furthermore, competing entropic and energy interactions generate a synergistic effect reducing the magnetic response of binary suspensions.

球状磁性ヤヌス粒子からなる分散系を対象にした擬2次元モンテカルロ・シミュレーション（磁気モーメントが粒子中心から横方向にずれた粒子モデル）

I have addressed a magnetic Janus particle suspension in the thermodynamic equilibrium situation. The magnetic moment of Janus particles treated in the present study is shifted from the particle center, which is perpendicular to the magnetic moment direction. From the viewpoint of elucidating the internal structure of particle aggregates in a three-dimensional (3D) system, I have treated a dispersion composed of magnetic Janus particles with a full 3D rotational ability in a quasi-two-dimensional (2D) system. The quasi-2D Monte Carlo simulations have been performed in order to investigate the dependence of a regime change in the aggregate structures on various factors such as the magnetic particle-particle interaction strength, magnetic particle-field interaction strength and the distance of the magnetic moment from the particle center. In no applied magnetic field, the Janus particles aggregate to form a stable cluster unit composed of 2-4 particles if the magnetic particle-particle interaction strength is increased. As the magnetic field is increased, the cluster units collapse and chain-like clusters are formed aligned in the magnetic field direction. In the situation of a strong magnetic field, the chain-like clusters composed of Janus particles tend to be thicker as the magnetic moment is shifted away from the particle center. This is because the magnetic interaction between neighboring particles increases due to the magnetic moments of constituent particles in chain-like clusters being closer to each other. The present results are useful for elucidating the internal structure of complex aggregates in a 3D system.

Multicore-based ferrofluids in zero field: initial magnetic susceptibility and self-assembly mechanisms.

The necessity to improve magnetic building blocks in magnetic nano-structured soft materials stems from a fascinating potential these materials have in bio-medical applications and nanofluidics. Along with practical reasons, the interplay of magnetic and steric interactions on one hand, and entropy, on the other, makes magnetic soft matter fundamentally challenging. Recently, in order to tailor magnetic response of the magnetic particle suspensions, the idea arose to replace standard single-core nanoparticles with nano-sized clusters of single-domain nanoparticles (grains) rigidly bound together by solid polymer matrix - multicore magnetic nanoparticles (MMNPs). To pursue this idea, a profound understanding of the MMNP interactions and self-assembly is required. In this work we present a computational study of the MMNP suspensions and elucidate their self-assembly and magnetic susceptibility. We show that depending on the magnetic moment of individual grains the suspensions exhibit qualitatively distinct regimes. Firstly, if the grains are moderately interacting, they contribute to a significant decrease of the remanent magnetisation of MMNPs and as such to a decrease of the magnetic susceptibility, this way confirming previous findings. If the grains are strongly interacting, instead, they serve as anchor points and support formation of grain clusters that span through several MMNPs, leading to MMNP cluster formation and a drastic increase of the initial magnetic response. Both the topology of the clusters and their size distribution in MMNP suspensions is found to be notably different from those formed in conventional magnetic fluids or magnetorheological suspensions.

The behavior and heat generation effect of a magnetic rod-like particle suspension in an alternating and a rotating magnetic field

We have investigated the behavior of magnetic rod-like particles and their relationship with the heat generation effect for both alternating and rotating magnetic fields, by means of Brownian dynamics simulations. As a common feature for both type of magnetic field variations, in the case of significantly strong particle-particle interaction strengths, densely-packed clusters are formed, which do not contribute to the heat generation. For the case of the alternating magnetic field, in the intermediate frequency range, linear thick chain-like clusters are formed and the constituent rod-like particles themselves tend to rotate to follow the change in the field. In contrast, for the case of the rotating field, linear clusters rotate as a whole body to respond to the magnetic field rotation. In both type of magnetic field variations, the magnetic interactions between the constituent particles in a cluster tend to function to suppress the relaxational motion of the rod-like particles, which, as a result, leads to increase in the heat generation effect in certain situations. In a relatively large frequency region, the rotating applied magnetic field gives rise to a larger heat generation effect, whereas in contrast, in the lower frequency region the alternating magnetic field yields the larger heating effect. Highlights The behavior of magnetic rod-like magnetic particles has been elucidated in the case of an alternating and a rotating magnetic field. The magnetic interactions between the constituent particles in a cluster tend to suppress the relaxation motion of the rod-like particles. The frequency and strength of a time-dependent magnetic field have complex influences on the heating effect. In a relatively large frequency region, the rotating applied magnetic field gives rise to a larger heat generation effect. In a relatively lower frequency region, the alternating magnetic field is superior to the rotating field.

An open-source automated magnetic optical density meter for analysis of suspensions of magnetic cells and particles.

We present a spectrophotometer (optical density meter) combined with electromagnets dedicated to the analysis of suspensions of magnetotactic bacteria. The instrument can also be applied to suspensions of other magnetic cells and magnetic particles. We have ensured that our system, called MagOD, can be easily reproduced by providing the source of the 3D prints for the housing, electronic designs, circuit board layouts, and microcontroller software. We compare the performance of our system to existing adapted commercial spectrophotometers. In addition, we demonstrate its use by analyzing the absorbance of magnetotactic bacteria as a function of their orientation with respect to the light path and their speed of reorientation after the field has been rotated by 90°. We continuously monitored the development of a culture of magnetotactic bacteria over a period of 5 days and measured the development of their velocity distribution over a period of one hour. Even though this dedicated spectrophotometer is relatively simple to construct and cost-effective, a range of magnetic field-dependent parameters can be extracted from suspensions of magnetotactic bacteria. Therefore, this instrument will help the magnetotactic research community to understand and apply this intriguing micro-organism.

Aggregation phenomena and regime change in a magnetic cubic particle suspension in an alternating magnetic field via quasi-two-dimensional Brownian dynamics

We have addressed the aggregation phenomena of a cubic haematite particle suspension in an alternating magnetic field in order to investigate the regime change in the aggregate structure. Brownian dynamics simulations have been performed for a quasi-two-dimensional system with an alternating magnetic field applied in the plane of the system. In a weak alternating field, the cubic particles aggregate to form closely-packed structures tending to an aligned face-to-face configuration with increasing magnetic particle-particle interaction strength. In a closely-packed cluster, the orientation of the magnetic moment of a constituent particle tends to be more strongly influenced by the magnetic interaction between neighbouring particles and less influenced by the direction of the alternating magnetic field. As the strength of the applied field is increased, the particle moments become more restricted to the direction of the alternating field and the closely-packed structures transform into elongated aggregates with an offset face-to-face configuration. As the direction of the alternating magnetic field switches from the positive to the negative x-direction, the elongated aggregates tend to collapse temporarily and when the orientation of the moments is again strongly restricted to the switched field direction, elongated aggregate structures with offset face-to-face contact are re-formed in the system. Highlights of the present paper We have investigated a regime change in the internal structure of cubic particle aggregates in an alternating magnetic field. As the magnetic field strength is increased, closely-packed aggregates with an aligned face-to-face configuration transform into elongated aggregates with an offset face-to-face configuration. We have clarified that the elongated aggregates collapse temporarily and then re-form when the direction of the alternating magnetic field switches. We have suggested that the frequency of the magnetic field may be used as a means for controlling the local internal structure of particle aggregates.

Chemically-adhesive particles form stronger and stiffer magnetorheological fluids

Magnetorheological fluids (MRFs) are suspensions of magnetic particles that solidify in the presence of a magnetic field due to the particles forming chains along field lines. The magnetic forces between particles dominate the solidification process and determine the yield stress of the resulting solid. Here, we investigate how reversible chemical links between particles influence MRF behavior in terms of their yield stress and stiffness through rheological testing in flow and oscillation mode. Initially, we functionalize particles with phosphonate groups that are expected to link through hydrogen bonding and find that this MRF exhibits up to 40% higher yield stress and 100% higher stiffness than an MRF composed of unfunctionalized particles. To explain this change, we model the chemical attraction as an adhesion that supplements dipole–dipole interactions between particles. Interestingly, we find that the increase in yield stress is largest for dilute suspensions that are expected to solidify into isolated chains, while the proportional increase in yield stress is less for MRF with higher concentrations. This is explained by the higher concentration MRF forming a body-centered tetragonal lattice in which interparticle adhesion forces are no longer aligned with the applied field. To explore the possibility of dynamically tuning interparticle interactions, we functionalize particles with polystyrene polymers with thymine terminal groups that will only exhibit interparticle hydrogen bonding in the presence of a small linking molecule, namely melamine. We find that MRF formed with these particles also exhibit up to a 40% increase in yield stress and ∼100% increase in stiffness for the polymer grafted particles in the presence of melamine, due to the formation of hydrogen bonding linkages between the thymine and melamine groups. In addition to confirming the role of hydrogen bonding in increasing MRF stiffness and yield stress, these results highlight the possibility of dynamically tuning MRF performance using magnetic fields and chemical modifications.