磁流变液组分对其沉降性影响的研究进展

磁流变液是一种形态和性能受外加磁场控制的新型智能材料。在汽车、建筑、医疗、航空航天多种领域具有重要的应用价值,但磁流变液沉降性问题一直是影响其广泛应用的难题。因此,首先从载液、磁性颗粒和添加剂三方面出发,简要回顾了近几年在磁流变液沉降性方面的研究,指出了影响磁流变液沉降性的因素主要有：载液的粘度、磁性颗粒的形状和尺寸、磁性颗粒与载液之间的密度差、添加剂的种类与添加量等。并给出了有效提高磁流变液沉降性的可行策略,最后从磁流变液的沉降现象与应用方面对沉降性研究进行了展望。     

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.     

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.     

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.     

Fabrication of liquid crystal Fe3O4 composites and their magnetorheological properties

Some supramolecular polyacrylate-based liquid crystal polymers (PLCPs) were prepared by polyacrylic acid, a liquid crystal monomer and 3,5-pyridinedicarboxylic acid. Series of magnetic liquid crystal particles (Fe₃O₄@PLCPs) with core-shell structure were prepared by modifying surface of magnetic nanoparticles Fe₃O₄ by the PLCPs. The Fe₃O₄@PLCPs showed a saturation magnetization strength above 51.17 emu/g, which is similar to pure magnetic Fe₃O₄, indicating good magnetism and magnetic field dependence. Series of magnetorheological fluids were fabricated by Fe₃O₄@PLCPs (using as dispersed phase) and silicone oil (using as carrier liquid). The effects of mesogen, magnetic particle, and the polymer matrix on magnetorheological performance and settling stability were investigated. The magnetorheological fluid based on 10% Fe₃O₄@PLCP-1 showed the best performance at an applied magnetic field of 100 mT in this study. Furthermore, the magnetorheological fluids showed excellent settling stability because the density of Fe₃O₄@PLCPs was lower than that of Fe₃O₄. The Fe₃O₄@PLCPs-based fluids presented certain application potential in the field of magnetic fluid due to the excellent magnetorheological effect and settling stability.     

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%.     

Magnetorheology of soft magnetic carbonyl iron suspension with single-walled carbon nanotube additive and its yield stress scaling function

The serious dispersion problem of carbonyl iron (CI) based magnetorheological (MR) fluid, due to the large density mismatch between CI particles and continuous medium, has hampered its MR applications. To resolve this undesirable sedimentation, we introduced fibrous single-walled carbon nanotube (SWNT) into CI suspension as additives. The dynamic yield stress change measured as a function of magnetic field strength was examined by adopting a universal equation which was originally applied for electrorheological (ER) fluids. In addition, the viscoelastic performances of CI/SWNT suspension were compared to investigate the influence of additives on the pristine CI suspension. The sedimentation ratio was also examined to confirm the role of submicron SWNT bundles.     

Synthesis and characterization of monodisperse magnetic composite particles for magnetorheological fluid materials

Monodisperse magnetic composite particles (MCP) were prepared and characterized for a study of magnetic field-responsive fluids. Magnetic composite particles used are iron oxide-coated polymer composite particles, which were synthesized through in situ coating of iron oxide onto pre-existing polymer particles by the reduction of ferrous fluids. For a uniform and bulk coating of iron oxide, the porous structure was introduced into the substrate polymer particles through a two-step seeded polymerization method. Moreover, surface cyano-functionality was born from acrylonitrile unit of substrate polymer and it played an important role in obtaining successful uniform coating. The structure of the composite particle was analyzed by using a thermo gravimetric analysis (TGA) and a X-ray diffraction (XRD) analysis. The magnetization property of the particle was also observed. Then, the rheological properties of monodisperse magnetorheological (MR) suspensions of magnetic composite particles were examined under a magnetic field using a parallel-plate type commercial rheometer. From the rheological measurements, it was found that MR properties of the magnetic composite suspensions are dependent on the iron oxide content and the fluid composition.     

聚乙二醇包裹羰基铁核壳粒子的制备及水基磁流变液的性能

以羰基铁粉(CI)为原料用共溶胶-凝胶反应制备CI/聚乙二醇核壳复合粒子，并将其与水组成了磁流变液. 用SEM、TEM、FT-IR和VSM表征了核壳复合粒子的微观结构和静磁特性，并测试了水基磁流变液的性能. 结果表明，核壳复合粒子表面有SiO_x和聚乙二醇的包覆层，它有较好的亲水性和优良的软磁特性，用它组成的水基磁流变液具有抗沉降性优良、零场粘度低、磁流变效应显著等特点.     

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.     

Application of Magnetorheological Fluid Damper in Rotor Vibration Control

A shear mode magnetorheological (MR) fluid damper used for rotor vibration control is designed, and the theoretical model of a cantilever rotor system with the MR fluid damper is established. The imbalance properties of the rotor system is studied theoretically and experimentally. It is found from the study that as the magnetic field strength in the MR fluid damper increases, the damping and stiffness of the damper are increased. The vibration amplitude of the rotor system is decreased at the critical speed, and the critical speed of the rotor system is increased with the increasing of applied magnetic field. The rotor vibration when passing through the critical speed can be controlled by using simple on/off control method.     

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.     

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.     

Analysis and Testing of Automotive MR Fluid Shock Absorber Based on Poiseuille Flow Mode

Analysis methodology and design theory of magnetorheological fluid (MR fluid) shock absorber based on of Poiseuille flow mode have been parented using Newton fluid model nonlinear Bingham plastic model. In the light of the technician requirements for Changan mini-automobile, a MR fluid shock absorber has been designed and fabricated using commercial MR fluid. We have validated experimentally the nonlinear MR fluid shock absorber model. The experimental results reveal that the analysis methodology and design theory is reasonable and the MR fluid shock absorber for a specific application can be designed according to the design methodology developed.     

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.     

Two-layer coating with polymer and carbon nanotube on magnetic carbonyl iron particle and its magnetorheology

Magnetic carbonyl iron (CI)-based magnetorheological (MR) fluids generally posses serious dispersion defects due to the large density mismatch between the CI particles and continuous oil medium, which restricts further MR applications. Polymer coating technology has been introduced in an attempt to reduce the density or prevent CI particle aggregation. In this study, a unique functional coating composed of a polyaniline layer and multiwalled carbon nanotube nest was fabricated on the surface of CI particles using a dispersion polymerization and solvent casting method to improve the sedimentation problem of CI-based MR fluids when dispersed in medium oil. The coating morphology was analyzed by scanning electron microscopy. The effect of the functional coating on the MR performance along with the sedimentation observations was investigated using a rotational rheometer. The results showed that the sedimentation of dispersed particles was improved considerably by the reduced density and rough morphology.     

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.     

Core–shell-structured silica-coated magnetic carbonyl iron microbead and its magnetorheology with anti-acidic characteristics

We synthesized silica-coated soft magnetic carbonyl iron (CI) particles through a modified Stöber method, in which the CI particles were pretreated with a grafting agent to enhance the affinity of a precursor of silica. Synthesized magnetic microbeads were characterized by scanning electron microscopy, energy dispersive X-ray spectroscopy, and anti-acid test in HCl solution. Silica-coated CI shows not only improved wettability to silicone oil with a lower off-state shear viscosity as a better magnetorheological fluid under an applied magnetic field but also enhanced anti-acidic property.     

Damping of Magnetorheological Elastomers

The damping property of magnetorheological (MR) elastomers is characterized by a modified dynamic mechanical-magnetic coupled analyzer. The influences of the external magnetic flux density, damping of the matrix, content of iron particles, dynamic strain, and driving frequency on the damping properties of MR elastomers were investigated experimentally. The experimental results indicate that the damping properties of MR elastomers greatly depend on the interfacial slipping between the inner particles and the matrix. Different from general composite materials, the interfacial slipping in MR elastomers is affected bythe external applied magnetic field.