Improved thermooxidation and sedimentation stability of covalently-coated carbonyl iron particles with cholesteryl groups and their influence on magnetorheology

Effect of the surface coating of carbonyl iron particles on the dispersion stability of magnetorheological fluid

The dispersion stability of carbonyl iron particle (CIP)-based magnetorheological fluid (MRF) is improved by CIP, which particle is etched with hydrochloric acid (HCl) to form porous structure with many hydroxyl groups and subsequently coated with silane coupling agents that have varying chain lengths. The microstructures, coating effect and magnetism of the CIPs were examined using the Scanning Electron Microscopy, Automatic Surface and Porosity Analyzer (BET), Fourier-Transform Infrared Spectroscopy, Thermogravimetric Analysis and Vibrating Sample Magnetometer. Furthermore, the rheological properties and dispersion stability of the MRFs were assessed using a Rotating Rheometer and Turbiscan-lab. The results revealed that the nanoporous structure appeared on the CIPs and the specific surface area increased remarkably after being etched by hydrochloric acid. Additionally, as the chain length of the silane coupling agent increases, the coated mass on the particles increases, the the density and the saturation magnetization of particles decreased, and the coated particles with different shell thicknesses were obtained; without a magnetic field, the viscosity of MRF prepared by coated particles increase slightly, due to the enhancement of special three-dimensional network structure; under a magnetic field, the viscosity of the MRF decreased distinctly; the sedimentation rate of MRF decreased from 58 to 3.5% after 100 days of sedimentation, and the migration distances of the MRFs were 22.4, 3.7, 2.4, and 0 mm, with particle sedimentation rates of 0.149, 0.019, 0.017, and 0 mm/h, respectively. The MRF with high dispersion stability was obtained, and the etching of CIP by HCl and the proper chain length of the coating of silane coupling agent were proved effective manners to improve the dispersion stability of MRF.

From Brush to Dendritic Structure: Tool for Tunable Interfacial Compatibility between the Iron-Based Particles and Silicone Oil in Magnetorheological Fluids

Comprehensive magnetic particle stability together with compatibility between them and liquid medium (silicone oil) is still a crucial issue in the case of magnetorheological (MR) suspensions to guarantee their overall stability and MR performance. Therefore, this study is aimed at improving the interfacial stability between the carbonyl iron (CI) particles and silicone oil. In this respect, the particles were modified with polymer brushes and dendritic structures of poly(2-(trimethylsilyloxy)ethyl methacrylate) (PHEMATMS), called CI-brushes or CI-dendrites, respectively, and their stability properties (corrosion, thermo-oxidation, and sedimentation) were compared to neat CI ones. Compatibility of the obtained particles and silicone oil was investigated using contact angle and off-state viscosity investigation. Finally, the magneto-responsive capabilities in terms of yield stress and reproducibility of the MR phenomenon were thoroughly investigated. It was found that MR suspensions based on CI-brushes had significantly improved compatibility properties than those of neat CI ones; however, the CI-dendrites-based suspension possessed the best capabilities, while the MR performance was negligibly suppressed.

Sedimentation Stability of Magnetorheological Fluids: The State of the Art and Challenging Issues

Among the many factors causing particle sedimentation, three principal ingredients are heavily involved: magnetic particles, a carrier liquid (base oil), and additives (surfactant). Therefore, many works have been carried out to improve the sedimentation stability of magnetorheological fluids (MRFs) by adopting the three methods. In the particle modification stage, the weight concentration, size distribution, particle shape, coated materials, and combinations of different sizes of the particles have been proposed, while for the modification of the carrier liquid, several works on the density increment, wettability control, and the use of natural oils, lubricant oil, grease, and ethyl- and butyl-acetate oils have been undertaken. Recently, in certain recipes to improve sedimentation stability, some additives such as aluminum stearate were used to increase the redispersibility of the aggregated particles. In addition, several works using more than two recipes modifying both the particles and base oils are being actively carried out to achieve higher sedimentation stability. This review article comprehensively introduces and discuses the recipes to improve sedimentation stability from the aspects of the three ingredients. A few conceptual methodologies to prevent the sedimentation occurring via a bottle's storage on the shelves of the application systems are also presented, since, to the author's knowledge, there has not been a report on this issue. These are challenging works to be explored and developed for successful application systems' MRFs.

Magnetizing Polymer Particles with a Solvent-Free Single Stage Process Using Superparamagnetic Iron Oxide Nanoparticles (SPION)s

Magnetic polymer composites are used in a variety of applications in many industries. Their production methods are usually time-consuming and solvent-intensive as they are performed in liquid phase processes, such as emulsion polymerization or precipitation. In this work, a quick, easy, and solvent-free method is presented to coat polymer particles with a discrete, non-coherent coating of superparamagnetic nanoparticles. The results of the dry coating process are evaluated optically, by means of scanning electron microscopy (SEM), via powder X-ray diffraction and thermally by means of differential scanning calorimetry, before finally demonstrating the effectiveness of dry coating by means of a vibrating sample magnetometer.

Atom Transfer Radical Polymerization of Pyrrole-Bearing Methacrylate for Production of Carbonyl Iron Particles with Conducting Shell for Enhanced Electromagnetic Shielding

The conducting polymer poly(2-(1H-pyrrole-1-yl)ethyl methacrylate (PPEMA) was synthesized by conventional atom transfer radical polymerization for the first time from free as well as surface-bonded alkyl bromide initiator. When grafted from the surface of carbonyl iron (CI) a substantial conducting shell on the magnetic core was obtained. Synthesis of the monomer as well as its polymer was confirmed using proton spectrum nuclear magnetic resonance (¹H NMR). Polymers with various molar masses and low dispersity showed the variability of this approach, providing a system with a tailorable structure and brush-like morphology. Successful grafting from the CI surface was elucidate by transmission electron microscopy and Fourier-transform infrared spectroscopy. Very importantly, thanks to the targeted nanometer-scale shell thickness of the PPEMA coating, the magnetization properties of the particles were negligibly affected, as confirmed using vibration sample magnetometry. Smart elastomers (SE) consisting of bare CI or CI grafted with PPEMA chains (CI-PPEMA) and silicone elastomer were prepared and dynamic mechanical properties as well as interference shielding ones were investigated. It was found that short polymer chains grafted to the CI particles exhibited the plasticizing effect, which might be interesting from the magnetorheological point of view, and more interestingly, in comparison to the neat CI-based sample, it provided enhanced electromagnetic shielding of nearly 30 dB in thickness of 500 μm. Thus, SE containing the newly synthesized CI-PPEMA hybrid particles also exhibited considerably enhanced damping factor and proper mechanical performance, which make the material highly promising from various practical application points of view.

Magnetite/Poly(ortho-anisidine) Composite Particles and Their Electrorheological Response

Magnetic and semiconducting Fe3O4/poly(o-anisidine) (POA) core/shell composite particles were fabricated by an oxidation process using Fe3O4 synthesized separately. The dispersion stability in a liquid medium and the electrical conductivity of synthesized particles were improved because of the conductive POA polymeric shell. The morphological, microstructural, compositional/elemental, and thermal behaviors of the particles were characterized using SEM with energy dispersive X-ray spectroscopy, TEM, XRD, and thermogravimetric analysis, respectively. A smart electro-magneto-rheological suspension containing Fe3O4/POA particles with two functionalities, magnetism and conductivity, was prepared. Its electrorheological properties were investigated at different electric field strengths using a rotational rheometer. Without an electric field, the sample demonstrated typical Newtonian fluid behavior, as expected. However, while under the electric field, it exhibited a solid-like behavior, and the dynamic (or elastic) yield stress of the ER fluid increased linearly as a function of the electric field strength in a power-law function with an index of 2.0, following the polarization mechanism.

Magnetorheological Fluids with Surface-Modified Iron Oxide Magnetic Particles with Controlled Size and Shape

This study is focused on surface-modified Fe₃O₄@SiO₂ particles with precisely controlled sizes and shapes applied in magnetorheological (MR) fluids. After the preparation of the monodisperse spindle-shaped and cubic Fe₃O₄@SiO₂ particles, surface modification with dodecyltrimethoxysilane (DTM) was carried out via a silane coupling reaction to increase the dispersion stability of the particles. Afterward, MR fluids were prepared by mixing the DTM-modified Fe₃O₄@SiO₂ particles with silicon oil. Transmission electron microscopy observations demonstrated that spindle-shaped Fe₃O₄@SiO₂ particles could form a more stable chain-like structure than cubic Fe₃O₄@SiO₂ particles upon application of an external magnetic field. The rheological measurements of MR fluids also indicated that the surface modification with DTM, the introduction of anisotropic shapes, and the increase in the particle size all played positive roles in the improvement in MR properties.

Magnetic Polymer Composite Particles: Design and Magnetorheology

As a family of smart functional hybrid materials, magnetic polymer composite particles have attracted considerable attention owing to their outstanding magnetism, dispersion stability, and fine biocompatibility. This review covers their magnetorheological properties, namely, flow curve, yield stress, and viscoelastic behavior, along with their synthesis. Preparation methods and characteristics of different types of magnetic composite particles are presented. Apart from the research progress in magnetic polymer composite synthesis, we also discuss prospects of this promising research field.

Magnetorheology: a review

Magnetic Soft Matter is a rapidly evolving discipline with fundamental and practical interest. This is due to the fact that its physical properties can be easily controlled through external magnetic fields. In this review paper, we revisit the most recent progress in the field (since 2010) emphasizing the rheological properties of these fascinating materials. New formulations and flow kinematics are discussed. Also, new members are integrated into the long-lived magnetorheology family and suggestions are provided for future development.

Highly stable and efficient electrorheological suspensions with hydrophobic interaction

HYPOTHESIS

Electrorheological fluid (ERF) is a kind of suspension or colloid composed of fine particles and insulating oil as continuous phase. The second miscible liquid phase with less affinity to the particles than the continuous phase is expected to influence particles aggregation, assembly and spanning mesostructures. Hence, it should be possible to tune the rheological and electrorheological properties and stability by the addition of second miscible liquid with different chain length and substituents.

EXPERIMENTS

We developed a giant ERF (GERF) with a binary liquid phase (BLP) by the addition of alkane to the silicone oil continuous phase. We studied the shear stress and viscosity under different shear rates, thixotropy and particle size distributions of these suspensions and characterized the concentration variation of GERFs under quiescent conditions by measuring the backscattering light intensity variation through vertical scanning.

FINDINGS

The dispersed particle size distribution is broadened, which produces higher static yield stress and lower zero-field viscosity than those of a single-liquid-phase GERF. The ER efficiency is much higher with the addition of alkane, reaching 10656, which is 1.8 times larger than that of single-liquid-phase suspensions. We performed 100-day stability testing and found that the GERF with 1-phenyldodecane showed excellent stability and performance.

Polymer-Magnetic Composite Particles of Fe₃O₄/Poly(o-anisidine) and Their Suspension Characteristics under Applied Magnetic Fields

Fe₃O₄/poly(o-anisidine) (POA) magnetic composite nanoparticles with their core-shell structure were synthesized by chemical oxidation polymerization technique and adopted as a magneto-responsive magnetorheological (MR) material. The chemical structure and morphology of core-shell nanoparticles were identified by FT-IR, SEM, TEM, and elemental analyzer. Pycnometer and vibrating sample magnetometer showed that the magnetic saturation and density of the Fe₃O₄/POA particles were reduced by the POA shell coatings. The rheological properties of the MR suspension dispersed in a silicone oil at various magnetic field strengths were investigated using a rotating rheometer under a magnetic field. The resulting MR suspension showed a typical Newtonian fluid behavior in the absence of external stimuli. When an external magnetic field was applied, it formed a strong chain structure, acting like a solid with a yield stress. Further solid-like behaviors were observed from storage shear relaxation and viscoelastic tests. Finally, the Fe₃O₄/POA nanoparticles showed better dispersion stability than pure Fe₃O₄ nanoparticles with 50% improvement.

Searching for a Stable High-Performance Magnetorheological Suspension

Magnetorheological (MR) fluids are a type of smart material with rheological properties that may be controlled through mesostructural transformations. MR fluids form solid-like fibril structures along the magnetic field direction upon application of a magnetic field due to magnetopolarization of soft-magnetic particles when suspended in an inert medium. A reverse structural transition occurs upon removal of the applied field. The structural changes are very fast on the order of milliseconds. The rheological properties of MR fluids vary with the application of a magnetic field, resulting in non-Newtonian viscoplastic flow behaviors. Recent applications have increased the demand for MR materials with better performance and good long-term stability. A variety of industrial MR materials have been developed and tested in numerous experimental and theoretical studies. Because modeling and analysis are essential to optimize material design, a new macroscale structural model has been developed to distinguish between static yield stress and dynamic yield stress and describe the flow behavior over a wide range of shear rates. Herein, this recent progress in the search for advanced MR fluid materials with good stability is described, along with new approaches to MR flow behavior analysis. Several ways to improve the stability and efficiency of the MR fluids are also summarized.

High-Performance Magnetorheological Suspensions of Pickering-Emulsion-Polymerized Polystyrene/Fe3O4 Particles with Enhanced Stability

The magnetorheological (MR) performance of suspensions based on core-shell-structured foamed polystyrene (PSF)/Fe₃O₄ particles was investigated by using a vibrating sample magnetometer and a rotational rheometer. Core-shell-structured polystyrene (PS)/Fe₃O₄ was synthesized by using the Pickering-emulsion polymerization method in which Fe₃O₄ nanoparticles were added as a solid surfactant. Foaming the PS core in PS/Fe₃O₄ particles was carried out by using a supercritical carbon dioxide (scCO₂) fluid. The density was measured by a pycnometer. The densities of PS/Fe₃O₄ and PSF/Fe₃O₄ particles were significantly lowered from that of the pure Fe₃O₄ particle after Pickering-emulsion polymerization and foaming treatment. All tested suspensions displayed similar MR behaviors but different yield strengths. The important parameter that determined the MR performance was not the particle density but rather the surface density of Fe₃O₄ on the PS core surface. The morphology was observed by scanning electron microscopy and transmission electron microscopy. Most Fe₃O₄ particles stayed on the surface of PS/Fe₃O₄ particles, making the surface topology bumpy and rough, which decreased the particle sedimentation velocity. Finally, Turbiscan apparatus was used to examine the sedimentation properties of different particle suspensions. The suspensions of PS/Fe₃O₄ and PSF/Fe₃O₄ showed remarkably improved stability against sedimentation, much better than the bare Fe₃O₄ particle suspension because of the reduced density mismatch between the nanoparticles and the carrier medium as well as the surface topology change.

Carbonyl iron coated with a sulfobetaine moiety as a biocompatible system and the magnetorheological performance of its silicone oil suspensions

In this study, surface modification of carbonyl iron (CI) particles with sulfobetaine moieties (SBE) was performed by the silanization of activated CI to form stable CI–SBE particles.

Fabrication of spherical CoFe2O4 nanoparticles via sol–gel and hydrothermal methods and investigation of their magnetorheological characteristics

CoFe₂O₄ nanoparticles are synthesized through sol–gel and facile hydrothermal methods, and their magnetorheological (MR) characteristics are evaluated.

Enhanced magnetorheological performance of highly uniform magnetic carbon nanoparticles

Magnetic carbon nanoparticles (MC NPs) are prepared on a multi-gram scale through carbonization of iron-doped polypyrrole nanoparticles (PPy NPs). Three different-sized MC NPs (ca. 40, 60 and 90 nm) are prepared and adopted as dispersing materials for magnetorheological (MR) fluids to investigate the influence of particle size on MR properties. The MC NP-based MR fluids exhibit outstanding MR performances compared to the conventional magnetic carbon material-based fluids. In addition, the MR activities are enhanced with decreasing particle diameter and increasing applied magnetic field strength. Furthermore, anti-sedimentation properties are examined in order to achieve in-depth insight into the effect of the particle size on MR fluids.

Pickering emulsion polymerized smart magnetic poly(methyl methacrylate)/Fe2O3 composite particles and their stimulus-response

Smart polymer/inorganic composite magnetic particles were synthesized by Pickering emulsion polymerization using magnetic iron oxide (Fe₂O₃) particles as a solid stabilizer.

The enhanced magnetorheological performance of carbonyl iron suspensions using magnetic Fe3O4/ZHS hybrid composite sheets

The facile two-step microwave-assisted synthesis of Fe₃O₄/ZHS hybrid composite sheets with 2D morphology considerably improves the MR performance and suspension redispersibility.

Graphene oxide based smart fluids

Graphene oxide (GO), a graphene-related material containing oxygen-functional groups, has attracted considerable attention because of its strongly hydrophilic behavior and potential use in GO-hybrid composites. We put our focus on the fabrication and rheological characteristics of GO-based electrorheological and magnetorheological smart fluids under electric and magnetic fields, respectively in this Highlight. A brief perspective on the significant role of GO in tribology and the amphiphilic characteristics of Pickering emulsions are also included.