Magnetorheological Performance Research Articles

Significant Improvement in Magnetorheological Performance by Controlling Micron Interspaces with High Permeability Submicron Particles.

The shear yield strength, sedimentation stability and zero-field viscosity of magnetorheological fluids (MRFs) are crucial for practical vibration damping applications, yet achieving a balanced combination of these performances remains challenging. Developing MRFs with excellent comprehensive performance is key to advancing smart vibration damping technologies further. Theoretically, incorporating a multiscale particle system and leveraging synergistic effects between their can somewhat enhance MRFs' performance. However, this approach often faces issues such as insignificant increases in shear yield strength and excessive rise in zero-field viscosity. In response, this study employs a DC arc plasma method to synthesize a high magnetic permeability, low coercivity submicron FeNi particles, and further develops a novel CIPs-FeNi bidisperse MRFs. The introduction of submicron FeNi particles not only significantly enhances the shear2019 yield strength of MRFs under low magnetic fields but also promotes improvements in sedimentation stability and redispersibility without excessively increasing viscosity. Comprehensive performance analysis is conducted to explore the optimal content ratio, and detailed mechanisms for the enhancement of performance are elucidated through analysis of parameters such as chain-like structure, magnetic flux density and friction coefficient. Most importantly, the superior comprehensive performance combined with straightforward fabrication methods significantly enhances the engineering applicability of the CIPs-FeNi bidisperse MRFs.

Fabrication and property research of a new 3D-Printable magnetorheological elastomer (MRE)

In order to meet the growing design demands for shape and structure of magnetic functional materials, particularly Magnetorheological Elastomers (MREs), additive manufacturing technology has been introduced into MRE production. Reported works of printable MRE (p-MRE) have successfully obtained high relative magnetorheological (MR) performance comparable to traditional MRE. However, there are still few studies on p-MRE with both high relative and absolute MR effects that is required for some applications such as intelligent dampers in automotive industry. In this study, polyurethane (TPU) and carbonyl iron powder (CIP) were utilized as raw materials to formulate p-MRE with high printability and high comprehensive MR performance. Based on the fused deposition modeling (FDM) process, a printing strategy suitable for this p-MRE material was determined through experimental design (DOE). The test result showed that the comprehensive MR performance of the p-MRE sheet samples obtained through linear printing path exceeded the majority of previously reported p-MRE materials. In addition, based on the analysis of the correlation between magnetic hysteresis like effect and MR effects, a circular printing path that may be beneficial for improving MR performance was proposed and corresponding p-MRE sheet sample was printed. The test results showed that compared with the linear printing path, the circular printing path further increases the comprehensive MR effect of the sheet sample to a maximum absolute MR effect of 4.2 MPa and a maximum relative MR effect of 620 %, which is comparable to most conventional MRE materials. Additionally, a theoretical framework associating magnetic field strength and filling density was proposed to explain peculiar phenomena observed in the experiments. On the basis of previous research on MREs and filler modified elastomers, a hypothesis was proposed to link magnetic field intensity with filler density, allowing the existing theory of filler modified elastomers to be used to explain the special phenomena observed in our experiments.

Fabrication of liquid crystal Fe3O4 composites and their magnetorheological properties

AbstractSome 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.

Liquid crystallinity and magnetorheological performance of polymeric liquid crystal magnetic composites

ABSTRACT Magnetorheological fluids (MRF) are regarded as a novel ‘intelligent’ material because they show the ability to respond to external stimuli. However, with the extension of working time, the agglomeration and sedimentation of magnetic particles become a serious problem, which has a great impact on the magnetorheological performance. Many methods have been proposed to overcome the particle settling problem, including magnetic particle modification and carrier liquid modification, but they all show negative effects on the magnetorheological performance of MRF. A new method to prepare the magnetic liquid crystal (LC) composites [PEA-COOH]SO3H@Fe3O4 series, with Fe3O4 nanoparticles as core and side-chain supramolecular LC polymers with different mesogen contents as coating, were reported. The chemical structure, magnetic property and LC properties were investigated by a variety of techniques. In order to study the effects of the mesogen content and LC phase state of magnetic LC composites on magnetorheological performance and sedimentation stability, MRF based on silicone oil carrier liquid and [PEA-COOH]SO3H@Fe3O4 dispersed phase were prepared. It was found that dynamic yield stress, plastic viscosity and the sedimentation ratio increased slightly with increasing mesogen content in the magnetic LC composites. What’s more, MRF prepared by magnetic LC composites annealed in LC state exhibited better magnetorheological performance and sedimentation stability than those in glassy state and isotropic state. These results indicated that the synergetic effects of LC orientation and magnetic field-induced arrangement of Fe3O4 magnetic particles can improve the magnetorheological performance and sedimentation stability of MRF.

Anisotropic nanoparticle-based magnetorheological elastomers: Effect of shape and orientation on the magnetorheological performance

Magnetorheological elastomers (MREs) respond to applied magnetic fields with a change in their mechanical properties. Within this work, iron oxide nanorods (IONRs) have been synthesized and the suitability of anisotropic nanoparticles to obtain highly responsive isotropic and anisotropic MREs has been demonstrated. Electron microscopy images show that the IONRs are well distributed inside the styrene-ethylene-butylene-styrene (SEBS) polymeric matrix and can be successfully oriented. The elastic modulus of the composites increases twofold with respect to the bare polymer. Room temperature magnetization loops of the composites show a difference in the orientations, with variations of the anisotropy field from 39.2 kA m−1 to 67.7 kA m−1. Magnetorheology measurements show that the relative magnetorheological effect experiences a twofold increase for the anisotropic MREs, from 8.3% to 17%. This, along with the improved mechanical properties of the anisotropic MREs, offers excellent possibilities for the design of high performance MREs that work optimally in the elastic region and possess improved applicability.

Magnetorheological study of core−shell structured carbonyl iron/2-D graphene oxide microparticles suspensions with improved sedimentation stability

This study aims to assess the rheological and stabilization characteristics of magnetorheological (MR) suspension by dispersing core–shell particles (graphene oxide (GO) as a shell and carbonyl iron (CI) as a core). A simple wet stirring technique was utilized to achieve the grafting of bare carbonyl particles (CIPs) with para-aminobenzoic acid (g-CIPs), and graphene oxide with concentrations of 1 and 2 wt%. The morphological, magnetization and elemental characteristics of prepared core–shell particles were analyzed by Field Emission Scanning Electron Microscopy (FE-SEM), Energy Dispersive Spectroscopy (EDS), powder X-Ray diffraction (XRD), Raman Spectroscopy and Fourier Transform Infrared Spectroscopy (FTIR). The encapsulation of grafted carbonyl iron particles with graphene oxide enhanced the surface roughness, while the structure of carbonyl iron particles retained its spherical shape. The presence of core–shell particles increased the affinity between the suspended particles and carrier oil, leading to better stability against sedimentation. The stability of prepared MR suspensions was examined by the visualization technique in which graphene oxide encapsulated carbonyl iron particles (GO@g-CIPs) showed remarkable improvement in sedimentation stability. The MR suspension is based on 1 wt% graphene oxide coated carbonyl iron particles (GO@g-CIPs-1) exhibits a sedimentation ratio of 44%, which is higher than that of the MR suspension based on 2 wt% graphene oxide coated carbonyl iron particles (GO@g-CIPs-2) (32%) and the MR suspension containing bare CIPs (20%). Finally, the magnetorheological study was carried out using a rotational rheometer. GO@g-CI based MR suspensions demonstrated a promising magnetorheological performance and identical MR characteristics, with varying yield stress.

Self-assembly and magnetorheological performance of Fe3O4-based liquid-crystalline composites

A new class of Fe3O4-based liquid-crystalline composites (Fe3O4@ILCPs) were constructed via a self-assembly process by using polyetheramine, liquid-crystalline monomer 3,3′-bis((cholesteryloxy)carbonyl)-[1,1′-biphenyl]-4,4′-dicarboxylic acid (BSI), adipic acid and magnetic nanoparticles Fe3O4. The cholesterol-based BSI content in the Fe3O4@ILCPs was varied in order to decipher the relationships between structure and thermal and magnetorheological properties on a molecular level. The increase in BSI component resulted in more rigid mesogens in ILCPs, as reflected by an increase in glass-transition temperature and isotropization temperature in differential scanning calorimetry analysis. The magnetorheological performance revealed that the Fe3O4@ILCPs-based magnetorheological fluids (MRFs) showed Bingham flow characteristics in the presence of external magnetic field. Under the same silicone oil carrier fluid and fixed magnetic field strength, the higher the content of magnetic particles was, the stronger the aggregation was between the Fe3O4@ILCPs particles and, as a result, the greater the shear stress and viscosity were. The Fe3O4@ILCP-1-based MRFs exhibited the highest shear stress and viscosity among the three MRFs (Fe3O4@ILCP-1, Fe3O4@ILCP-2 and Fe3O4@ILCP-3-based MRFs) at a fixed shear rate suggested that Fe3O4@ILCP-1 containing more bulky ionic mesogen is favorable for liquid crystal orientation and synergistically interactions with magnetic particle Fe3O4 alignment induced by magnetic field. The sedimentation measurements suggested that MRFs showed good sedimentation stability due to the network structure of Fe3O4@ILCPs particles and the reduction of density mismatch between carrier fluid and magnetic nanoparticles.

Stable Magnetorheological Fluids Containing Bidisperse Fillers with Compact/Mesoporous Silica Coatings.

A drawback of magnetorheological fluids is low kinetic stability, which severely limits their practical utilization. This paper describes the suppression of sedimentation through a combination of bidispersal and coating techniques. A magnetic, sub-micro additive was fabricated and sequentially coated with organosilanes. The first layer was represented by compact silica, while the outer layer consisted of mesoporous silica, obtained with the oil–water biphase stratification method. The success of the modification technique was evidenced with transmission electron microscopy, scanning electron microscopy/energy-dispersive X-ray spectroscopy and Fourier-transform infrared spectroscopy. The coating exceptionally increased the specific surface area, from 47 m2/g (neat particles) up to 312 m2/g, which when combined with lower density, resulted in remarkable improvement in the sedimentation profile. At this expense, the compact/mesoporous silica slightly diminished the magnetization of the particles, while the magnetorheological performance remained at an acceptable level, as evaluated with a modified version of the Cross model. Sedimentation curves were, for the first time in magnetorheology, modelled via a novel five-parameter equation (S-model) that showed a robust fitting capability. The sub-micro additive prevented the primary carbonyl iron particles from aggregation, which was projected into the improved sedimentation behavior (up to a six-fold reduction in the sedimentation rate). Detailed focus was also given to analyze the implications of the sub-micro additives and their surface texture on the overall behavior of the bidisperse magnetorheological fluids.

Enhanced performances of magnetorheological fluids based on weakly magnetic organogel

NHT/Fe3O4 composite particles with fairly low saturationmagnetization were prepared by in-situ co-precipitation method in this work, then these composite particles were dispersed in non-magnetic base oil to prepare weakly magnetic organogel. Experimental results testify that this organogel is magnetic sensitive and reveal an obvious shear-thinning behavior and structural recover ability under shear and magnetic field. Afterwards, ferromagnetic particles were mixed into above organogel to make magnetorheological fluids. By performing a comparative study of MRFs based on different carrier, enhanced magnetorheological performances and suspension stability of MRFs based on weakly magnetic organogel were confirmed. Besides, MRFs based on weakly magnetic organogel have significantly increased shear stresses and yield stresses especially in the presence of magnetic field. A point-dipole model is applied to explain above experimental phenomena, the possible reason is that composite particles squeeze into field-induced chains driven by hydrodynamic force and magnetostatic force therefore apply additional forces on ferromagnetic particles. Under such circumstance, stronger and more cross-linked field-induced microstructures are established, as a result, leading to enhanced magnetorheological performances macroscopically. Besides, microstructures formed by composite particles impose the gap among ferromagnetic particles thus hinder their direct contact and aggregation. Hence, an enhanced suspension stability of MRFs based on weakly magnetic organogel was also observed in this work.

Characteristic analysis under small-stroke and medium-high frequency of magneto-rheological damper with pressure controlled mechanism

Due to the high frequency hardening effect in applications of satellite and precision vibration isolation, it is an urgent need to analyze and improve the magnetorheological (MR) performance of MR damper under small-stroke and medium-high frequency excitations. In this paper, a compact MR damper with pressure controlled mechanism is proposed, analyzed and tested. Considering the inertial, pre-compression and compressibility of MR fluid, the dynamic physic model is established to analyze the output characteristics with pre-compressions under small-stroke and medium-high frequency excitations. And then, the critical model between the pre-yield region and post-yield region is obtained. The critical boundary between different excitations is derived and comparatively analyzed. Finally, the experiments with the proposed MR damper are carried out. Compared with theoretical results, the damping force and dynamic stiffness increase with the increase of the applied current and excitations. Besides these, the energy dissipated performance can be improved by the pre-compression. When the initial pressure increases to 5 MPa with the fixed frequency of 10 Hz, the energy dissipation is increased by 43.5%. So the pre-compression is an effective way to solve the high frequency hardening. Besides these, the derived critical model can predict the performance of MR damper at different excitations.

Poly(N-methylaniline)/magnetite microsphere and its electrical and magnetic dual responses

Dual electric/magnetic field-responsive magnetite coated poly(N-methylaniline)/magnetite (PNMA/Fe3O4) microspheres were synthesized via a straightforward synthetic route of chemical oxidative polymerization for monodispersed PNMA microspheres and chemical co-precipitation of Fe3O4 onto the PNMA surface. Along with their chemical and physical characterizations such as morphology, size, and crystalline structure, the electrical conductivity, magnetic properties, and dielectric properties were investigated using a low resistivity meter, vibrating sample magnetometry, and an LCR meter, respectively. All tests and analyses on the particles have proved that they have been successfully synthesized and have good magnetic saturation and dielectric properties. Studies have shown that PNMA had an appropriate conductivity so that these particles do not need for de-doping for electrorheological (ER) test. On the other hand, as a superior soft magnetic material, Fe3O4 has a good magnetic susceptibility for magnetorheological (MR) performance. The synthesized PNMA/Fe3O4 microspheres were adopted in both ER and MR fluids. The suspension made of the PNMA/Fe3O4 particles with a volume fraction of 10 vol% showed a good dual ER and MR response via a rotational rheometer. It is also found that the yield stress of ER and MR fluids followed a power-law behavior under electric/magnetic field strength with their slopes of 1.5 and 1.0, respectively. Thus, the synergistic effects of Fe3O4 and PNMA with both electrical and magnetic behaviors demonstrate their suspension possessing both ER/MR characteristics, widening their potential engineering applications.

Mechanical properties of magneto-sensitive shear thickening fluid absorber and application potential in a vehicle

A multifunctional smart material with both shear thickening effect and magnetorheological performance was fabricated by dispersing carbonyl iron powder (CIP) particles into shear thickening fluid, the properties and application potential were tested and analysed. Firstly, the rheological properties of this type of magneto-sensitive shear thickening fluid (MSTF) was tested by a rheometer. Besides, the influence of the current, frequency and amplitude on the mechanical properties of the absorber with MSTF was studied. Finally, the damping force and the variation rules of the Cadillac shock absorber with commercial magnetorheological fluid and MSTF were tested, compared and analysed at different currents and distinct velocities. The influence of the shear thickening effect of MSTF on the damping force in the shock absorber was studied by testing the self-made MSTF and MRF with the CIP fraction from 10% to 70%. This work provided a design idea to improve the shock absorber performance.

Strong and Stable Magnetorheological Fluids Based on Flaky Sendust-Co0.4Fe0.4Ni0.2 Nanocomposite Particles.

The magnetorheological (MR) performance of suspensions based on magnetic (flaky Sendust (FS))-magnetic (Co0.4Fe0.4Ni0.2) nanocomposite particles was investigated by using a vibrating sample magnetometer and a rotational rheometer. Flaky Sendust@Co0.4Fe0.4Ni0.2 nanocomposite particles were fabricated through wet chemical synthesis of Co0.4Fe0.4Ni0.2 on the surface of FS. The density of the resultant FS@Co0.4Fe0.4Ni0.2 was less than that of FS due to the pore/void formation in the composite particles. Because of the high saturation magnetization of Co0.4Fe0.4Ni0.2 (165 emu/g), FS@Co0.4Fe0.4Ni0.2 (145 emu/g) exhibited greater magnetization than bare FS (130 emu/g), which resulted in the good performance of FS@Co0.4Fe0.4Ni0.2-based MR fluids: the suspension exhibited a remarkably high yield stress, almost one order greater than that of MR fluids based on hierarchically structured (HS) Fe3O4 particles. In addition, the high drag coefficient of FS@Co0.4Fe0.4Ni0.2 in the liquid medium, in conjunction with its lower density, resulted in a substantially improved long-term stability, better than that of Co0.4Fe0.4Ni0.2- or FS-based suspensions. Although the density of the FS@Co0.4Fe0.4Ni0.2 nanoparticles is higher than that of HS-Fe3O4 particles, their stability is much better than the stability of HS-Fe3O4 particle's suspension. Manufactured magnetic-magnetic nanocomposite particles provide a feasible MR suspension of high MR performance and long-term stability.

Enhanced Magnetorheological Performance of Carbonyl Iron Suspension Added With Barium Ferrite Nanoparticle

Hard-magnetic barium ferrite (BF) nanoparticles with a hexagonal plate-like structure were used as an additive to a carbonyl iron (CI) microparticle-based magnetorheological (MR) fluid. The morphology of the pristine CI and CI/BF mixture particles was examined by scanning electron microscopy. The saturation magnetization and coercivity values of each particle were measured in the powder state by vibrating sample magnetometry. The MR characteristics of the CI/BF MR fluid measured using a rotation rheometer under a range of magnetic field strengths were compared with those of the CI-based MR fluid. The flow behavior of both MR fluids was fitted using a Herschel–Bulkley model, and their stress relaxation phenomenon was examined using the Schwarzl equation. The MR fluid with the BF additive showed higher dynamic and elastic yield stresses than the MR fluid without the BF additive as the magnetic field strength increased. Furthermore, the BF nanoparticles embedded in the space between the CI microparticles improved the dispersion stability and the MR performance of the MR fluid.

The Preparation of multifunctional shear thickening fluid and the application in shock absorber

A multifunctional shear thickening fluid (MSTF) that exhibits both shear thickening (ST) effect and magnetorheological (MR) performance was prepared. The MR effect of MSTF was compared with magnetorheological fluid (MRF) when the CIP mass fraction varies from 10% to 70%. The results show that the MR effect of MSTF is higher than that of MRF obviously. Besides, the compression force and rebound force of the damper containing MSTF and MRF were tested and compared when the current was set as 0, 0.5, 1.0, 1.5, 2.0, 2.5 and 3A. When the CIP mass fraction is less than 30%, the forces of these two kinds of materials are almost the same at any current value. And as the CIP mass fraction is more than 30%, the rebound force of MSTF is obviously higher than that of MRF.

Porous Fe3O4 submicron particles for use in magnetorheological fluids

The magnetorheological (MR) performance and stability of various suspensions based on core-shell-structured polystyrene(PS) / Fe3O4 particles, the Fe3O4-coated particles, the hollow and porous Fe3O4-particles were investigated by using a rotational rheometer and Turbiscan, while magnetic properties of all the magnetic particles used were examined by using a vibrating sample magnetometer (VSM). The PS (core)/Fe3O4(shell) was synthesized by the Pickering-emulsion polymerization method using Fe3O4 nanoparticles as a solid surfactant. Hollow and porous Fe3O4 nanoparticles were obtained after extraction of the core PS phase by Soxhlet extractor. The density of the hollow Fe3O4 nanoparticles was markedly decreased compared to that of pure Fe3O4, but slightly increased compared to that of the PS/Fe3O4 particle. All suspensions, prepared by dispersing the synthesized particles in the liquid medium (silicone oil), exhibited similar MR behaviors, but the MR performance of the hollow and porous Fe3O4 particle suspension was remarkably better than that of the PS/Fe3O4 particle suspension. The hollow Fe3O4 particle suspension showed a significantly better stability than the pure Fe3O4 particle suspension due to the reduced density mismatch between the particle and the liquid medium and the rough and bumpy surface morphology. The optimal density for the MR performance and the suspension stability was determined from the MR property analysis.

Effect of Fe₃O₄ Nanoparticles on Magnetorheological Properties of Flake-Shaped Carbonyl Iron Water-Based Suspension

To analyze the effect of magnetite Fe <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</sub> O <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">4</sub> disk-shaped nanoparticles with flake-shaped microparticles in water-based magneto rheological (MR) suspension, the rheological properties were studied using a parallel plate rheometer. The morphology, crystallinity, and magnetic property of the prepared MR suspensions were examined by field emission scanning electron microscopy (FESEM), X-ray diffraction, and vibrating sample magnetometer, respectively. In the presence of a magnetic field, micron-sized carbonyl iron (CI) particles lead to form a robust columnar structure with Fe <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</sub> O <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">4</sub> nanoparticles and enhanced the magnetorheological performances. The magnetorheological performances of MR suspensions were examined in shear rate, shear strain, and shear stress testing sweep modes with and without a magnetic field. It was observed that adding the 1 wt% of Fe <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</sub> O <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">4</sub> , the magnetorheological performance of MR suspension enhanced. The MR fluid with CI/Fe <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</sub> O <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">4</sub> nanoparticle mixture showed significantly higher shear viscosity and shear stress and yielded stresses than pure CI-based MR fluid. The yield stresses were higher in the shear rate sweep mode than strain and stress sweep testing modes.

The study of enhancement of magnetorheological effect based on natural rubber/thermoplastic elastomer SEBS hybrid matrix

Magnetorheological elastomers are one kind of smart materials which consist of matrix materials and magnetic particles. The mechanical properties of magnetorheological elastomers were controllable under an external magnetic field. Applications of magnetorheological elastomers are limited as a result of their poor magnetorheological effect and mechanical performance, so enhancing the magnetorheological effect of them is critical for their application. Styrene-ethylene-butylene-styrene based thermoplastic elastomer was added to natural rubber to fabricate hybrid matrix–based magnetorheological elastomers. Zero modulus of magnetorheological elastomers increased from 0.50 to 0.64 MPa and magnetorheological effect increased from 28.00% to 43.75% with the addition of styrene-ethylene-butylene-styrene based thermoplastic elastomer. The contact angle of carbonyl iron particles with the matrix showed that styrene-ethylene-butylene-styrene based thermoplastic elastomer can improve the compatibility of carbonyl iron particles with the matrix. Fourier-transform infrared spectroscopy analysis has been carried out to investigate the internal structure of hybrid matrix–based magnetorheological elastomers.

High-Performance Magnetorheological Suspensions of Fe3O4-deposited Carbon Nanotubes with Enhanced Stability

AbstractThe magnetorheological (MR) performance of suspensions based on the Fe3O4-deposited carbon nanotubes (CNTs) was investigated by using a vibrating sample magnetometer (VSM) and a rotational rheometer. The Fe3O4-deposited CNTs were synthesized by the reduction process in which nano-Fe3O4 nanoparticles were generated and adsorbed on the surface of CNTs. All tested suspensions displayed excellent MR behaviors with high yield strengths. The morphology was observed by scanning electron microscope (SEM) and transmission electron microscope (TEM). It was revealed that Fe3O4 particles adsorbed on the surface of CNT particles led to make the surface topology bumpy and rough which decreased the particle sedimentation velocity. Finally, Turbiscan apparatus was used to test the sedimentation properties of Fe3O4-deposited CNTs suspensions. The suspensions showed excellent stability against sedimentation, much better than bare Fe3O4 particle suspension due to the inherent low density of CNT and its inside pore which can reduce the density mismatch between the nanoparticles and the carrier medium as well as the surface topology change due to the adsorption of Fe3O4.

Tailoring Performance, Damping, and Surface Properties of Magnetorheological Elastomers via Particle-Grafting Technology.

A novel concept based on advanced particle-grafting technology to tailor performance, damping, and surface properties of the magnetorheological elastomers (MREs) is introduced. In this work, the carbonyl iron (CI) particles grafted with poly(trimethylsilyloxyethyl methacrylate) (PHEMATMS) of two different molecular weights were prepared via surface-initiated atom transfer radical polymerization and the relations between the PHEMATMS chain lengths and the MREs properties were investigated. The results show that the magnetorheological performance and damping capability were remarkably influenced by different interaction between polydimethylsiloxane chains as a matrix and PHEMATMS grafts due to their different length. The MRE containing CI grafted with PHEMATMS of higher molecular weight exhibited a greater plasticizing effect and hence both a higher relative magnetorheological effect and enhanced damping capability were observed. Besides bulk MRE properties, the PHEMATMS modifications influenced also field-induced surface activity of the MRE sheets, which manifested as notable changes in surface roughness.