Magnetoviscous Effect Research Articles

Rotational dynamics of magnetic nanoparticles in different matrix systems

Abstract Dynamic magnetic measurements on magnetic nanoparticle (MNP) samples have been widely used for the determination of structural MNP parameters as well as for the realization of bioassays. On the other hand, proposed that the MNPs are thermally blocked, i.e., that the dynamics are dominated by the Brownian rotation, and knowing the distribution of their hydrodynamic size, information on the matrix properties can be obtained. In contrast to conventional rheology, the local environment of the MNPs is sensed on the nanoscale so that important information on the embedding of MNPs in the matrix and thus the particle-matrix interaction is obtained. Depending on the characteristic length scales of the matrix and the size of the MNPs, rheological parameters, such as viscosity and shear modulus, derived from nanorheological measurements can differ from the values obtained from conventional rheology. To measure the MNP dynamics, different experimental techniques can be applied. In this contribution, the focus lies on ac susceptometry and fluxgate magnetorelaxometry. The analysis of the complex ACS spectra is generally carried out within a modified Debye model. Different approaches for the estimation of rheological parameters from the complex ACS spectra will be presented. Two model systems will exemplarily be discussed in detail. As a Newtonian matrix system, water-glycerol mixtures were studied. It is demonstrated that the dynamic viscosity can accurately be estimated from ACS measurements on well thermally blocked single-core as well as on multicore MNP systems, which include Brownian and Néel dynamics. As a viscoelastic matrix system, aqueous gelatin solutions were studied. Gelatin is known to be a Voigt-Kelvin model system, in which elastic and viscous forces are parallel. In particular, we studied the gelation dynamics by repetitive measurements of the complex ACS spectrum. Different approaches to derive viscosity and shear modulus are applied and compared. In order to identify magnetoviscous effects in dynamic magnetic measurements, the magnetic field dependence of the Brownian relaxation time has to be eliminated. ACS measurements on various sufficiently strongly diluted aqueous MNP suspensions were performed in dependence of ac field amplitude and superimposed dc field strength and compared to theory. Excellent agreement was found.

Electropermanent magnet-driven droplet size modulation for two-phase ferromicrofluidics

A new ferrofluidic droplet generator is demonstrated using an electropermanent magnet to change the viscosity of the ferrofluid oil phase in a flow-focusing junction, which enables control of the aqueous droplet size. Electropermanent magnets are capable of fast switching (< 100 $$\upmu$$ s) and have magnetic field strengths comparable to those of permanent magnets. When switched on, the magnetoviscous effect increases the viscosity of the ferrofluid, thus increasing the channel’s fluidic resistance, slowing the flow rate of the oil-based phase and changing the droplet diameter. We have demonstrated on-demand droplet size modulation as large as 44% at speeds fast enough to modulate the size of a single droplet in a stream. Due to compliance in the supply tubing and Polydimethylsiloxane (PDMS) microfluidic channels, the change in droplet size relaxes with a time scale of seconds. An application of droplet size modulation was demonstrated by integrating a passive size-based magnetic droplet sorting stage.

Magnetoviscous effects on revolving ferrofluid due to an immersed rotating rod in the presence of gravitational force

In the present investigation, the effects of the rotating magnetic field, magnetization body force, and magnetic torque on revolving ferrofluid due to an immersed rotating rod are considered. The impact of the rotation of the rod and gravitational force are taken into deliberation in the present physical model. A similarity transformation is used to transform the governing partial differential equations into a set of nonlinear-coupled differential equations in dimensionless form. The numerical solution of the transformed nonlinear-coupled differential equations is obtained using COMSOL Multiphysics software in a framework of the finite element method. Results for radial, tangential, and axial velocity distributions are presented for different values of ferromagnetic interaction number, effective magnetization number, the volume concentration of particles, gravitational number, and speed of the rotation of the immersed rod. Coefficients of skin friction on the surface of the disk and wall of the rod are also computed for different values of considered physical parameters. Present results show that magnetic torque creates an additional resistance on the velocity distributions.

Rheological implications of the inclusion of ferrofluids and the presence of uniform magnetic field on heavy and extra-heavy crude oils

This study embraces the evaluation of the rheological and magneto-rheological properties of heavy and extra-heavy crude oils by applying nanotechnology and magnetism as technological solutions in reducing viscosity. Mixtures of heavy oils with ferrofluids were used to study the viscous effects induced by the action of external magnetic fields. The rheological evaluation covered rotational and oscillatory tests as a function of time and temperature. In the magneto-rheological characterization, there were analyzed the magnetoviscous effects. The results revealed that the crude oils are viscoelastic materials that follow the Generalized Maxwell Model over a wide range of temperatures (-5 to 60 °C). It was also proved that the synergy between the carrier liquid and the nanoparticles promoted a significant reduction of viscosity (~98–99%) and viscoelasticity, which was directly related to the simultaneous action of the solvent and the asphaltene adsorption onto the nanoparticles surface. Critical concentrations of nanoparticles (0.2 wt% and 0.6 wt%) were proved to promote the maximum decrease in viscosity (additional ~ 0.3–0.5% or 1000-3000 cP) and the elastic storage modulus, which was crucial evidence of their effect on hindering the aggregation mechanisms of asphaltenes. In the heavy oil–ferrofluid mixtures, a magneto-rheological effect was demonstrated. The magnetic field attenuated the initial relaxation processes, leading to an increase in the viscosity and shear stress. The phenomenon was attributed to the formation of magnetic chains, such as that observed in magneto-rheological fluids. These results were supported by Scanning Electron Microscopy, which showed the formation of magnetic-field induced thick columnar assemblies of nanoparticles-asphaltene complexes.

Frequency Dispersion of the Coefficient of Shear Viscosity and the Magnetic Viscous Effect in Magnetic Liquids

Dynamic expressions for bulk and shear viscosity coefficients are obtained on the basis of statistical theory and a model of a two-component system. The dependence of the coefficients of shear viscosity of magnetic fluids based on water, kerosene, and undecane on the frequency and magnitude of an external magnetic field is calculated from the selection of potential energies for intermolecular and dipole–dipole interactions, the radial distribution functions, and the effect of an external magnetic field. The regions of frequency dispersion for the coefficients of shear viscosity of the studied fluids are determined, and the magneto–viscous effect in magnetic fluids is considered.

Modeling and experiments of capillary flow of non-symmetric magnetic fluids under uniform field

The present work aims to investigate the flow of a non-symmetric ferrofluid undergoing a uniform magnetic field in axial symmetry through both theoretical and experimental approaches. The magneto viscous effect is investigated for a fully developed laminar flow. The governing equations are made non-dimensional in order to identify the physical non-dimensional numbers such as the Péclet number, the particle volume fraction and the parameter of effective applied magnetic field. A regular perturbation method is used to obtain new asymptotic solutions on the limits of very low and very high Péclet numbers. Additionally, numerical integration of the equations system provides a solution for the entire range of Péclet. The magnetization profiles and more global quantities like wall viscosity and the relative viscosity are determined. The numerical and asymptotic solutions present an excellent agreement in the application range of the asymptotic solution. Finally, the magneto viscous effect in capillary flow is also determined through an experimental investigation, showing a very good agreement with the asymptotic solution corresponding to the limit of a low Péclet number.

Relating magnetization, structure and rheology in ferrofluids with multi-core magnetic nanoparticles

Due to their magnetic moments solubilized magnetic nanoparticles are able to spontaneously assemble into dipolar mesostructures, which affect the flow behavior. Multi-core magnetic nanoparticles developed for biomedical applications have enhanced magnetic properties and show significant magnetoviscous effect, but the quantitative interpretation of this phenomenon is incomplete. We apply rheological measurements, magnetic granulometry and dimensional scaling to show the existence of a master curve for magnetorheology of these materials. Using the developed approach the magnetoviscous effect can now be interpreted in a unified way within the stochastic chain model.

Experimental Investigations on the Effect of Axial Homogenous Magnetic Fields on Propagating Vortex Flow in the Taylor-Couette System.

Experimental investigations of propagating vortex flow states (pV states) in a short Taylor–Couette system with asymmetric boundary conditions are presented. The flow state was established in a ferrofluid showing no magneto-viscous effect and was exposed to axial magnetic fields. It was found that the magnetic field led to a change in the spatial and temporal behavior of the pV state, indicating complex interactions between the flow field and magnetic field. A stepwise applied axial magnetic field destabilized the pV state, leading to an intermittent flow state. Gradually increasing the axial magnetic fields changed the temporal behavior of the regime. Up to magnetic field strengths of 20 kA/m, the orbital frequency, as a measure for the temporal periodicity, was increased with field strength.

First-principles magnetization relaxation equation of interacting ferrofluids with applications to magnetoviscous effects

Magnetization relaxation equation (MRE) plays a primary role in numerous phenomena and applications involving ferrofluid dynamics. However, as yet there exist no MREs derived from first principles and applicable to concentrated and strongly interacting ferrofluids. In this paper, we derive a novel MRE based on the projection operator technique. It sufficiently accounts for interparticle correlations beyond the scope of previous models. The MREs by Martsenyuk, Raikher, and Shliomis and by Zubarev and Yushkov (ZY), respectively, for ideal and weakly nonideal (WNI) ferrofluids, are recovered as low-order approximations. We also investigate the magnetoviscous effects. For the first time, we unveil qualitatively the different roles played by short- and long-range interparticle correlations. The long-range correlation effect dominates in a WNI ferrofluid, and both our MRE and the ZY model are in quantitative agreement with simulations on field-dependent rotational viscosity. However, for strongly nonideal ferrofluids, short-range correlations can become substantial and compete with long-range correlations to reduce rotational viscosities. Our MRE is the first dynamic model faithfully capturing both short- and long-range correlations, thereby applicable to ferrofluids characterized by a broad range of concentrations and interacting strengths. It is expected to be a cornerstone for quantitative modeling of the dynamic response of ferrofluids to external fields or flow deformations. Because most commercial ferrofluids are designed to be strongly nonideal to enhance magnetic response, our theory may provide fresh insights for applications of realistic ferrofluids in industry and biomedicine.

Magnetic Field Effect on Thermal, Dielectric, and Viscous Properties of a Transformer Oil-Based Magnetic Nanofluid

Progress in electrical engineering puts a greater demand on the cooling and insulating properties of liquid media, such as transformer oils. To enhance their performance, researchers develop various nanofluids based on transformer oils. In this study, we focus on novel commercial transformer oil and a magnetic nanofluid containing iron oxide nanoparticles. Three key properties are experimentally investigated in this paper. Thermal conductivity was studied by a transient plane source method dependent on the magnetic volume fraction and external magnetic field. It is shown that the classical effective medium theory, such as the Maxwell model, fails to explain the obtained results. We highlight the importance of the magnetic field distribution and the location of the thermal conductivity sensor in the analysis of the anisotropic thermal conductivity. Dielectric permittivity of the magnetic nanofluid, dependent on electric field frequency and magnetic volume fraction, was measured by an LCR meter. The measurements were carried out in thin sample cells yielding unusual magneto-dielectric anisotropy, which was dependent on the magnetic volume fraction. Finally, the viscosity of the studied magnetic fluid was experimentally studied by means of a rheometer with a magneto-rheological device. The measurements proved the magneto-viscous effect, which intensifies with increasing magnetic volume fraction.

From high colloidal stability ferrofluids to magnetorheological fluids: tuning the flow behavior by magnetite nanoclusters

The flow behavior of practically structureless ferrofluids was tuned over a large range by adding well-defined amounts of magnetite nanoparticle clusters. Magnetite nanoparticle clusters with hydrophobic coating were dispersed in high colloidal stability transformer oil based ferrofluid samples, initially free of clusters. The resulting ferrofluid composition consists both of single (approx. 7 nm mean size) and clustered (280 nm average size) magnetite nanoparticles, each of them in a prescribed amount. This new approach allows a precise evaluation of the role of clusters on the ferrofluid flow behavior. The magnetite nanoparticle clusters obtained by a solvothermal method have a saturation magnetization of 75 emu g−1 and a remnant magnetization of 0.2 emu g−1 due to the large size (∼25 nm) of the magnetite nanoparticles in their composition. Long bundles of thin elongated needle like aggregates of magnetic nanocluster particles are formed in a magnetic field and produce a significant magnetorheological response of the bidisperse magnetic suspensions observed already for moderate applied magnetic field values. The dynamic yield stress and magnetoviscous effect are analyzed and compared with previous results concerning suspensions of micrometer size iron particles in a ferrofluid carrier. The viscoelastic properties and the interactions between the components of ferrofluid based magnetite nanoparticle cluster suspensions were evaluated by creep tests in zero and non-zero applied magnetic field. The bidisperse magnetic nanocomposite suspensions investigated provide a promising new formulation of MR fluids with improved kinetic stability to be used in seismic dampers and flow control devices.

Influence of the Carrier Fluid Viscosity on the Rotational and Oscillatory Rheological Properties of Ferrofluids.

This work mainly presents a comprehensive experimental study on the magnetorheological behavior of ferrofluids with carrier fluids of different viscosities. Three lubrication oil based ferrofluids of different viscosities and similar saturation magnetization values were prepared and characterized. Static and dynamic rheological tests of the three ferrofluids were performed using an advanced rotational rheometer with a magnetic field generating module. According to the experimental results, the magneto viscous effect, yield stress and storage modulus increase with the viscosity of carrier fluid, indicating that the structures of ferrrofluids tend to be larger and more stable in a carrier fluid with larger viscosity. The emergence and growth of "crossover" region with the increase in carrier fluid viscosity was observed using the strain-rate frequency superposition method, which were explained according to the microscopic mechanism of magnetorheology. These findings contribute to a better understanding of the microscopic mechanism of magnetorheology and provide guidance for practical applications.

Rheological behavior of magnetic colloids in the borderline between ferrofluids and magnetorheological fluids

Magnetic colloids were formulated by dispersion of magnetic oxide spheres in water. Their rheological behavior was investigated for a wide range of particle diameters covering in detail the magnetic single-multidomain transition and therefore spanning the gap between ferrofluids and conventional magnetorheological fluids. The magnetoviscous effect (i.e., the ratio between the viscosity increment under field and the viscosity value in the absence of field) was found to reach a maximum for a critical particle size in the single-multidomain transition region. The observations were explained in terms of magnetization changes with particle size. The results obtained are applicable to any magnetic material (not only iron oxides) and therefore constitute a new route to enhance the magnetorheological effect. For very small particle sizes (in the superparamagnetic region), thermal motion plays a crucial role and the dimensionless viscosity scales with the Peclet number as expected for Brownian Hard Spheres. For larger particle sizes and λ&amp;gt;1, the dimensionless viscosity scales with the Mason number and closely follows the structural viscosity model under the mean magnetization approximation.

Study on MHD Cylindrical Couette Flow and Rheological Properties of Some Magnetic Suspensions

The study of magnetic suspensions (MS) and magnetic field effects on their rheological properties is of evident practical importance due to its ability to orient and change their physical properties, especially their viscosity, by magnetic fields. This research presents the effect of a uniform magnetic field on the flow of MS in the annular region between two concentric cylinders. The motion of the fluid is due to the rotation of the inner cylinder with a constant angular velocity. An exact solution of the governing equations is obtained in the form of modified Bessel functions of the first and second kinds. The torque, which must be applied to the inner cylinder in order to maintain the rotation, is also calculated. The results show that as the magnetic parameter increases, the velocity profile decreases, while the torque increases due to the effect of magnetic force against the flow direction.&#x0D; In order to model the magnetoviscous effects, experiments were performed for different shear rates and different magnetic field strengths by using specially designed rheometers. The studied samples are iron oxide-water-glycerol system, ferrofluid nanoparticles, MAG DX biocompatible ferrofluid. The theoretical analysis is based on Giesekus model for MS. This model gives more accurate results and takes into account the effects of viscoelastic shear thinning characteristics. It is found that a magnetic field increases the viscosity of all suspensions under consideration. Finally, new proposed correlation for the viscosity of MS as a function of both shear rate and magnetic field has been suggested.

Magnetoviscous effect investigation of water based Mn-Zn Fe2O4 magnetic nanofluid under the influence of magnetic field: An experimental study

Abstract This experimental study presents the magnetoviscous effect of water based Mn-Zn Fe2O4 with C-TAB as surfactant under the influence of magnetic fields. Mn-Zn Fe2O4 magnetic nanoparticles have been synthesized and characterized using correspondingly co-precipitation method and XRD, SEM and VSM analysis. Effect of various parameters like flow shear rate (0.1–1000 1/s), nanoparticle volume concentration (0.0–0.6%), sample temperature (20–60 °C) and magnetic field (0–600 A/m), has been investigated. The results show that, for the cases without magnetic field, the viscosity behaves shear thinning, Newtonian and shear thickening at respectively low, moderate, and high shear rate values. With applying magnetic fields, the larger the field strength the larger the viscosity value. Also, with nanoparticle volume fraction augmentation as well as field increase, the two shear thinning and shear thickening behaviors have been augmented; Finally, an empirical correlation is proposed to predict magnetoviscous behavior of the ferrofluid as function of the various mentioned parameters. This correlation can be helpful in thermomagnetic convection investigations.

Magnetoviscous effect in case of magnetic fluid oscillations in strong magnetic field

Magnetoviscous effect in case of magnetic fluid oscillations in strong magnetic field

Investigation on Magnetoviscous Effects of Water-Based Magnetic Fluid

Magnetic fluid or called ferro-fluid is such kind of magnetic nanomaterials, which is stable of solid-liquid two phase colloidal solution composited by magnetic nanoparticles coated by surfactant and highly disperse in a carrier liquid. The basis of magnetic fluid widely applied mainly is due to their unique magnetic properties and rheological properties, which enable its action as intelligent control materials in the magnetic field so as to achieve the goal of magnetic liquid dynamic seal, magnetic damping vibration and so on. In our recent research, the water-based magnetic fluid was synthesized using a co-precipitation method and its magnetorheological properties were studied. During the process, the magnetorheological properties of stable water-based magnetic fluids were determined by magnetic rheometer. The results show that the shear-thinning behavior of magnetic fluids was observed both in the absence and presence of magnetic field. However, there was a remarkable magnetoviscous effect with magnetic field function and the unexpected variation of shear stress was related to the chain aggregation. Furthermore, the constitutive equation of water-based magnetic fluid at a low magnetic field was discussed.

Dipolar Interaction and Magneto-Viscoelasticity in Nanomagnetic Fluid.

We investigate the effect of dilution on dipolar interaction with linear and non-linear rheological properties of kerosene based magnetic fluid. The steady-state behavior demonstrate a shear thinning behavior and corroborated with a power law, (η = c <mml:math display="block"> <mml:mover accent="true"> <mml:mi>γ</mml:mi> <mml:mo>˙</mml:mo> </mml:mover></mml:math>n + η∞) exponent, n ≤ 1. The shear-induced-breakup (separation) of nanoparticles and the yielding behavior has been explained by Bingham model. Moreover, the magnetoviscous effect showed an initial increase at low shear rate and decrease at higher shear rate. Further, specific viscosity (ηF)-versus-Mason number (Mn) shows a perfect scaling at lower Mn (≤10-4) confirming negligible thermal and colloidal forces. Whereas, at higher Mn (≥10-3) deviation from collapse indicates the dominance of Brownian forces acting on nanofluids. The magnetic field dependent elastic (G') and viscous (G″) modulus reveal a crossover from viscoelastic-to-viscous behavior of nanofluid at critical concentration. Finally, we compare viscoelastic results with De Gans diagonal scaling theory to correlate the functional dependence of storage and loss modules with different particle volume concentration.

Rheological and Thermal Transport Characteristics of a Transformer Oil Based Ferrofluid

Ferrofluids based on insulating liquids are intensively studied as a potential substitute of liquid dielectric in high voltage technologies. In this work we focus on the experimental investigation of flow and thermal transport characteristics of a ferrofluid based on transformer oil (Mogul) and iron oxide nanoparticles. The magneto-rheological behavior of the ferrofluid was studied by a rotational rheometer in the shear rate range from 1 to 1000 s-1 and magnetic field up to 1 T. By means of a thermal constants analyzer and a transient plane source method we obtained the thermal conductivity, specific heat and thermal diffusivity values for the studied oil and the ferrofluid. It is shown that the Newtonian character of the ferrofluid changes to a non-Newtonian with application of the magnetic field. The notable magneto-viscous effect has been observed especially at low shear rates. We found that the doping of the transformer oil by 3 wt% of the nanoparticles results in a thermal conductivity enhancement by about 3.2%. (Less)

Influence of Particle Size Distribution of Magnetic Fluid on the Resistance Torque of Magnetic Fluid Seal

Magnetic fluid seal is widely used in military and aerospace industry owing to its zero leakage property, long life and reliability. The resistance torque is often required to be small and stay within allowable scope with the standing time expanding and the working environment changing. In this paper, we discussed the influence of the particle size distribution of magnetic fluid on the resistance torque of magnetic fluid seal. Samples of magnetic fluid of different particle size distribution were processed by applying a magnetic field gradient. Afterwards, the rheological property of different samples was analyzed using rheometer. Besides, the resistance torque of magnetic fluid seal on different occasions was measured. We explained these results from the point of formation and destruction of magnetic aggregations based on the theory of magnetoviscous effect, thus provided feasible ways to improve the performance of magnetic fluid seal.