Research on Control Method for MR Damper

The relation between drive current and damper force was developed and a controller of MR damper was successfully designed. The experimental results indicated the controller’s outputs have good performance with rapid response speed and high precision. The control effect on MR damper is excellent.     

Additive role of attapulgite nanoclay on carbonyl iron-based magnetorheological suspension

Attapulgite (ATP), a fibrous nanoclay mineral, was adopted as an additive in this study to improve the sedimentation problem of soft magnetic carbonyl iron (CI)-based magnetorheological (MR) fluids caused by the density mismatch between the CI particles and medium oil. The MR characteristics of the two MR fluid systems with and without ATP were measured and compared using a rotational rheometer under different magnetic field strengths. Scanning electron microscopy indicated that ATP filled the interspaces among the CI particles, explaining the improved dispersion stability of the MR fluid based on the Turbiscan sedimentation measurements. Despite the slight decrease in MR characteristics, the MR fluid with the additive exhibited the typical MR performance of an increase in shear stress in an applied magnetic field.     

Soft magnetic carbonyl iron microsphere dispersed in grease and its rheological characteristics under magnetic field

Magnetorheological (MR) grease, comprised of a suspension of soft magnetic carbonyl iron (CI) microspherical particles dispersed in a grease medium, was fabricated by a mechanical stirring method. As potential medium oil for MR system, shear viscosity of the pure grease was measured as a function of temperature. Its MR characteristics were investigated using a rotational rheometer under an external magnetic field. Flow curve responses (shear stress and shear viscosity), yield stress, and elasticity were investigated using various magnetic field strengths ranging from 0 to 342 kA/m. It was confirmed that MR grease has a yield stress under no external magnetic field due to the inherent property of grease. In addition, CI based MR grease exhibited a characteristic of a Bingham fluid.     

Nano-sized Fe soft-magnetic particle and its magnetorheology

As a new magnetoresponsive magnetorheological (MR) material under an applied magnetic field, magnetic Fe nanoparticles were synthesized from a simple process of thermal decomposition of pentacarbonyl iron using oleyl amine and kerosene at 150 °C. Morphology of the fabricated Fe nanoparticle was examined using both scanning electron microscopy and transmission electron microscopy. MR characteristics of the nano-sized magnetic particle-based MR fluid dispersed in non-magnetic carrier fluid was investigated using a rotational rheometer under different external magnetic field strengths, focusing on their flow behaviors at a steady shear mode and yield stress. Flow curve was also found to be fitted well with the Casson equation.     

Effect of carbon black on the mechanical performances of magnetorheological elastomers

Several magnetorheological elastomer (MRE) samples, with different weight percentages of carbon black, were fabricated under a constant magnetic field. Their microstructures were observed by using an environmental scanning electron microscope (SEM), and their mechanical performance including magnetorheological (MR) effect, damping ratio and tensile strength were measured with a dynamic mechanical analyzer (DMA) system and an electronic tensile machine. The experimental results demonstrate that carbon black plays a significant role in improving the mechanical performance of MR elastomers. Besides the merits of high MR effect and good tensile strength, the damping ratio of such materials is much reduced. This is expected to solve a big problem in the application of MR elastomers in practical devices, such as in adaptive tuned vibration absorbers.     

Atom transfer radical polymerized PMMA/magnetite nanocomposites and their magnetorheology

We synthesized core/shell-typed magnetic nanoparticle composites using poly(methyl methacrylate) (PMMA) as a shell and magnetite nanoparticle (MN) as a core, in which the PMMA shell was prepared via atomic transfer radical polymerization (ATRP) method. Chemical structure and morphology of the synthesized MN–PMMA nanocomposite were investigated using FT-IR and TEM, respectively. Magnetorheological (MR) fluid was prepared by dispersing synthesized MN–PMMA in non-magnetic medium. Both shear stress and shear viscosity of the MR fluids as a function of shear rate were measured using a rotational rheometer with a magnetic field generator, exhibiting that a yield stress increased with an external magnetic field strength.     

有机分子修饰铁粒子表面改善水基磁流变液的抗氧化性和稳定性

采用有机分子N-葡萄糖基乙二胺三乙酸(GED3A)修饰羰基铁(CI)粒子表面的方法, 制备了复合磁性粒子(CMPs)和水基磁流变(MR)液; 用扫描电镜(SEM)、振动样品磁强计(VSM)和带磁场供应和控制器的流变仪表征了CMPs及水基MR液的性能; 同时, 通过稳定性试验、空气氧化试验、酸腐蚀试验分别分析了水基MR液的分散稳定性和抗氧化性. 结果表明, 用此方法制备的CMPs具有良好的软磁性能, 饱和磁化强度(Ms)为182.2 emu·g-1, 矫顽力(Hc)为4.17 Oe, 剩磁(Mr)为0.1944 emu·g-1. 与原CI粒子水基MR液比较, 制备的水基MR液的沉降率下降了约24.4%; 在酸的浓度为0.02-0.10 mol·L-1范围内, 抗HCl氧化的能力提高了92.6%-95.7%, 抗HNO3氧化的能力提高了86.1%-93.8%.     

The Preparation of Light Magnetic Materials and it's Application on Magnetorheological Fluids

It is reported that preparation of magnetic material(nickel and cobalt) on the surface of light material. The density of the new material is low (Effective density of it is 2~3 g/cm3). The sedimental stability of the new magnetorheological fluid made by light magnetic material is similar to that of the MR fluid made by carbonyl nickel powders containing lots of anti-sedimental agent. The apparent viscosity of new MR fluids under magnetic field is dozens of times as high as the inital viscosity. Therefore the problem of settling of solid particles under gravity can be effectively prevented by manufacturing magnetorheological fluids using the new material.     

Microfluidic capturing-dynamics of paramagnetic bead suspensions

We study theoretically the capturing of paramagnetic beads by a magnetic field gradient in a microfluidic channel treating the beads as a continuum. Bead motion is affected by both fluidic and magnetic forces. The transfer of momentum from beads to the fluid creates an effective bead-bead interaction that greatly aids capturing. We demonstrate that for a given inlet flow speed a critical density of beads exists above which complete capturing takes place.     

Iron oxide/MCM-41 mesoporous nanocomposites and their magnetorheology

Mesoporous nanocomposite materials of magnetic iron oxide-containing MCM-41 (IO/MCM-41) were prepared by simple thermal oxidation of Fe-containing MCM-41 initially prepared by a direct synthesis route using Fe³⁺ salt. The magnetic saturation of the fabricated nanocomposite materials was measured using a vibrating sample magnetometer, while surface morphology and inner framework of the composite materials were studied using a field emission scanning electron microscope and a transmission electron microscope to confirm their mesoporous nanocomposite formation. The fabricated magnetic materials were then adopted as a magnetorheological (MR) fluid, where the IO/MCM-41 magnetic nanocomposites were dispersed in a nonmagnetic medium oil in addition to as an additive for carbonyl iron-based MR fluid. Their MR properties of flow curve along with yield stress and viscoelastic properties under applied magnetic fields were investigated using a rotational rheometer.     

Magnesium ferrite nanocrystal clusters for magnetorheological fluid with enhanced sedimentation stability

In this study, magnesium ferrite (MgFe₂O₄) nanocrystal clusters were synthesized using an ascorbic acid-assistant solvothermal method and evaluated as a candidate for magnetorheological (MR) fluid. The morphology, microstructure and magnetic properties of the MgFe₂O₄ nanocrystal clusters were investigated in detail by field emission scanning electron microscopy (FESEM), transmission electron microscope (TEM), thermogravimetric analyzer (TGA), X-ray diffraction (XRD) and superconducting quantum interference device (SQUID). The MgFe₂O₄ nanocrystal clusters were suspended in silicone oil to prepare MR fluid and the MR properties were tested using a Physica MCR301 rheometer fitted with a magneto-rheological module. The prepared MR fluid showed typical Bingham plastic behavior, changing from a liquid-like to a solid-like structure under an external magnetic field. Compared with the conventional carbonyl iron particles, MgFe₂O₄ nanocrystal clusters-based MR fluid demonstrated enhanced sedimentation stability due to the reduced mismatch in density between the particles and the carrier medium. In summary, the as-prepared MgFe₂O₄ nanocrystal clusters are regarded as a promising candidate for MR fluid with enhanced sedimentation stability.     

Magnetic orientation of diamagnetic amorphous polymers

Molecular order in an amorphous polymer with anisotropic magnetic susceptibility is altered by applying external magnetic fields. Disks of atactic polystyrene (a‐PS) are prepared by solvent casting outside or inside a magnet. The effect of the magnetic field on the polymer samples is investigated by magnetic levitation and solid state NMR spectroscopy. Magnetic levitation of the a‐PS disks shows that the orientation of disk symmetry axis with respect to the magnetic field gradient depends on the magnitude and direction of the applied field during casting. Similarly, carbon‐13 two‐dimensional cross‐polarization/magic angle spinning rotor‐synchronized NMR measurements in these samples show modulation patterns of the spinning side bands only on disks prepared in the presence of a magnetic field. These findings suggest that macromolecular order could be induced in a fluid or fluid–solid phase transition with cooperative segmental motions reorienting the diamagnetic susceptibility tensor to minimize the magnetic contribution to free energy of the sample. © 2010 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 48: 1009–1015, 2010     

Ultrathin polydimethylsiloxane-coated carbonyl iron particles and their magnetorheological characteristics

An ultrathin polydimethylsiloxane (PDMS) layer with a mean thickness of 1 nm was coated on soft magnetic carbonyl iron (CI) particles by using a simple thermal evaporation process, and then their physical characteristics were examined using scanning electron microscopy (SEM), X-ray photoelectron spectroscopy (XPS), thermal gravimetry analysis (TGA), and vibrating sample magnetometry (VSM). Magnetorheological (MR) fluid was prepared by using PDMS-coated CI powder, and its rheological behavior was investigated under different external magnetic field strengths using a rotational rheometer. The CI particles coated by a thin PDMS layer showed higher oxidation temperature than pristine CI particles and MR fluid consisting of PDMS-coated CI particles demonstrated better dispersion stability in a nonmagnetic carrier fluid.     

Rapid linear scale-up of a protein separation by centrifugal partition chromatography

The scaling up of the separation of two proteins with an aqueous two-phase system (ATPS) from 176 mg with a 500 ml laboratory scale centrifugal partition chromatography (CPC) column to 2.2g with a 6.25 litre pilot-scale column is presented. A model sample system of a mixture of lysozyme and myoglobin was chosen for this study using an ATPS system comprising 12.5% (w/w) PEG-1000:12.5% (w/w) K2HPO4. It was found that the maximum sample concentration possible without precipitation was 2.2mg/ml for each constituent. The optimisation of rotor speed, mobile phase flow rate and sample loading was performed on a laboratory-scale device. It was found that a centrifuge speed of 2000 rpm (224 'g'), 10 ml/min mobile phase flow rate with a 43 ml (10% of active column volume) sample volume gave optimum operating conditions. This was linearly scaled up to pilot scale by increasing mobile phase flow rate, fraction size and sample loading in the ratio of the system capacities (i.e. 12.5:1). Flow rate was therefore increased from 10 ml/min to 125 ml/min, fraction size from 10 ml to 125 ml and sample loading from 43 ml to 500 ml. Rotor speed however was reduced from 2000 rpm on the laboratory device to 1293 rpm on the pilot-scale device to maintain the same 224 'g' field in each chamber, as the pilot-scale CPC unit has a larger rotor radius than the laboratory one. Resolution increased from Rs=1.28 on the 500 ml rotor to Rs=1.88 on the 6.25 litre rotor, giving potential throughputs in batch mode of over 40 g/day.     

Experimental characterization and viscoelastic modeling of isotropic and anisotropic magnetorheological elastomers

The paper presents experimental research and numerical modeling of dynamic properties of magnetorheological elastomers (MREs). Isotropic and anisotropic MREs have been prepared based on silicone matrix filled by micro-sized carbonyl iron particles. Dynamic properties of the isotropic and anisotropic MREs were determined using double-lap shear test under harmonic loading in the displacement control mode. Effects of excitation frequency, strain amplitude, and magnetic field intensity on the dynamic properties of the MREs were examined. Dynamic moduli of the MREs decreased with increasing the strain amplitude of applied harmonic load. The dynamic moduli and damping properties of the MREs increased with increasing the frequency and magnetic flux density. The anisotropic MREs showed higher dynamic moduli and magnetorheological (MR) effect than those of the isotropic ones. The MR effect of the MREs increased with the rise of the magnetic flux density. The dependence of dynamic moduli and loss factor on the frequency and magnetic flux density was numerically studied using four-parameter fractional derivative viscoelastic model. The model was fitted well to experimental data for both isotropic and anisotropic MREs. The fitting of dynamic moduli and loss factor for the isotropic and anisotropic MREs is in good agreement with experimental results.     

Nanodrop of an Ising magnetic fluid on a solid surface

The density functional theory of inhomogeneous simple fluids is extended to an Ising magnetic fluid in contact with a solid surface, which is subjected to an external uniform or nonuniform magnetic field. The system is described by two coupled integral equations regarding the magnetic moment and fluid density distributions. The dependence of the contact angle that a nanodrop makes with the solid surface on the parameters involved in the magnetic interactions between the molecules of fluid and between the molecules of fluid and an external magnetic field is calculated. For the uniform magnetic field, the contact angle increases with increasing magnetic field, approaching an asymptotic value that depends on the strength of the fluid-fluid magnetic interactions. In the nonuniform field generated by a permanent magnet, the contact angle first increases with increasing magnetic field B(M) and then decreases, with the decrease being almost linear for large values of B(M). The obtained results are in qualitative agreement with the experimental data on the contact angle of magnetic drops on a solid surface available in the literature.     

Pickering emulsions with controllable stability

We prepare solid-stabilized emulsions using paramagnetic particles at an oil/water interface that can undergo macroscopic phase separation upon application of an external magnetic field. A critical field strength is found for which emulsion droplets begin to translate into the continuous-phase fluid. At higher fields, the emulsions destabilize, leading to a fully phase-separated system. This effect is reversible, and long-term stability can be recovered by remixing the components with mechanical agitation.     

Xanthan gum-coated soft magnetic carbonyl iron composite particles and their magnetorheology

The dispersion stability of carbonyl iron (CI)-based magnetorheological (MR) fluid was improved by coating soft magnetic CI particles with an environmentally benign biopolymer of xanthan gum to reduce the density gap between the medium oil and dispersed particles. The sedimentation test of the MR fluid showed that the xanthan gum/CI composite particles improved the sedimentation drawback of the pristine CI-based MR fluid. The rheological properties of the MR fluid were also examined using a rotational rheometer to observe the typical MR characteristics, such as yield stress and shear viscosity.     

Heterocoagulation in Bidisperse Magnetorheological Fluids Containing Like-Charged Nanosized and Micron Particles Without a Magnetic Field

Based on extended Derjaguin–Landau–Verwey–Overbeek theory, a heterocoagulation model is proposed for magnetorheological (MR) fluids containing like-charged nanosized and micron particles without a magnetic field. This model considers three major interactions, namely van der Waals attraction, electrical double layer (EDL) interaction, and steric repulsion. The EDL interaction has been identified as the most important factor. The surface potential ratio β (ψ₂/ψ₁) between two dissimilar particles with like charge plays an important role in controlling the change of EDL interaction. At higher β ratios, the EDL interaction becomes attractive when the surface separation falls within a certain range. Two groups of MR fluid samples have been used in experimental studies based on electroacoustic measurements. In the first group, the ratio and the sum of the zeta potentials between carbonyl iron particles and ceria were 4 and ?734.57 mV, respectively. In the second group, these parameters were 1.38 and ?108.17 mV, respectively. The experimental results suggested that the second group did not undergo heterocoagulation, whereas the first group showed extensive heterocoagulation. The difference in surface potentials between particles of two different phases has been found to be critical for determining the state of dispersion or heterocoagulation in concentrated MR fluid systems.     

Destabilizing effect of time-dependent oblique magnetic field on magnetic fluids streaming in porous media

The present work studies Kelvin-Helmholtz waves propagating between two magnetic fluids. The system is composed of two semi-infinite magnetic fluids streaming throughout porous media. The system is influenced by an oblique magnetic field. The solution of the linearized equations of motion under the boundary conditions leads to deriving the Mathieu equation governing the interfacial displacement and having complex coefficients. The stability criteria are discussed theoretically and numerically, from which stability diagrams are obtained. Regions of stability and instability are identified for the magnetic fields versus the wavenumber. It is found that the increase of the fluid density ratio, the fluid velocity ratio, the upper viscosity, and the lower porous permeability play a stabilizing role in the stability behavior in the presence of an oscillating vertical magnetic field or in the presence of an oscillating tangential magnetic field. The increase of the fluid viscosity plays a stabilizing role and can be used to retard the destabilizing influence for the vertical magnetic field. Dual roles are observed for the fluid velocity in the stability criteria. It is found that the field frequency plays against the constant part for the magnetic field.