Core–shell-structured Fe3O4 nanocomposite particles for high-performance/stable magnetorheological fluids: preparation and characteristics

Abstract

Magnetorheological (MR) fluids are a type of smart material of which rheological properties can be controlled through mesostructural transformations. They are generally magnetically responsive particle suspensions, which consist of magnetizable particles dispersed in a non-magnetic liquid medium. Ferromagnetic or ferrimagnetic particles with a micrometer size are suitable for MR fluid suspensions, since they can be polarized by the external magnetic field to form chain-like aggregates (mesostructures) that have a strong yield strength and can induce a high shear viscosity. Fe 3 O 4 particles are good candidates for high-performance MR materials due to their low density and high magnetic properties as well as their excellent surface activities. To improve the stability of the MR suspension, many studies on the synthesis of Fe 3 O 4 -containing nanocomposites have been carried out recently. This review deals with the latest advances in the fabrication of Fe 3 O 4 nanocomposite particles with a core-shell structure as well as their critical characteristics and advantages to be used in MR suspensions. We focused on the synthesis strategy of various Fe 3 O 4 nanoparticles with a core-shell structure as well as their performance in the magnetic fields.

Effect of Particle Shape Anisotropy on the Performance and Stability of Magnetorheological Fluids

“…4,12−18 Various attempts to resolve the sedimentation problem in MR fluids by, for example, incorporating additives that support the solid-like structure (mesostructure) or wrapping the magnetic particles with an organic polymer layer have been reported. 17,18 Composite materials with various structures (core−shell structures, magnetic particlesdecorated fibers and tubes, and hollow structures) with low density were prepared by combining magnetic particles with lightweight materials such as polymers, SiO 2 , and carbon materials and subsequently investigated as MR fluids. 19−26 Recently, an effective method to fabricate core−shell structure particles, the Pickering emulsion process, has been intensively investigated to take advantage of solid particles as a surfactant.…”

“…However, MR fluids of magnetic particles exhibit poor long-term stability (particle sedimentation) because of the difference in density between the magnetic particles and the liquid medium. ,− Various attempts to resolve the sedimentation problem in MR fluids by, for example, incorporating additives that support the solid-like structure (mesostructure) or wrapping the magnetic particles with an organic polymer layer have been reported. , Composite materials with various structures (core–shell structures, magnetic particles-decorated fibers and tubes, and hollow structures) with low density were prepared by combining magnetic particles with lightweight materials such as polymers, SiO 2 , and carbon materials and subsequently investigated as MR fluids. − Recently, an effective method to fabricate core–shell structure particles, the Pickering emulsion process, has been intensively investigated to take advantage of solid particles as a surfactant. − The nanometer-sized solid particles are positioned at the interface to reduce the interfacial energy. After the emulsion polymerization, core (polymer)–shell (solid surfactants) particles are obtained.…”

“…The suspension performance of the magnetic material can then be improved by exploiting the shape anisotropy effect. We have also observed in our previous studies that particles’ surface topology can considerably delay their sedimentation because of the enhanced dragging on the surface. − Because the drag coefficient of a particle depends on both its shape and surface roughness, a change in particle shape will affect the stability of the suspension. , Most previous studies on MR fluids focused on developing synthetic routes to magnetic particles to improve the long-term stability of the fluids. ,− By contrast, studies that focus on the particle shape have been less common, partly because of a lack of suitable nonspherical particles with an appropriate size, that is, small enough to prevent sedimentation but large enough to achieve sufficient magnetic force to overcome thermal motion. − …”

Hierarchically Structured Fe3O4 Nanoparticles for High-Performance Magnetorheological Fluids with Long-Term Stability

“…It is a kind of smart material due to its rapid response to an external magnetic field. 5,6 Once the magnetic field is turned on, the magnetic particles in MR fluids are aggregated to form chainlike structures due to magnetic dipole interactions between the particles along the field direction. 7,8 The chainlike structures (meso-structures) increase the viscosity of MR fluids very quickly by the transformation of the MR fluid from a liquidlike viscous state to a solidlike elastic state in milliseconds.…”

“…Smart materials, whose properties varies with external stimuli, have been applied in various industrial field due to their quick responsiveness. − A magnetorheological (MR) fluid consists of magnetic particles dispersed in a nonmagnetic carrier medium. It is a kind of smart material due to its rapid response to an external magnetic field. , Once the magnetic field is turned on, the magnetic particles in MR fluids are aggregated to form chainlike structures due to magnetic dipole interactions between the particles along the field direction. , The chainlike structures (meso-structures) increase the viscosity of MR fluids very quickly by the transformation of the MR fluid from a liquidlike viscous state to a solidlike elastic state in milliseconds. − Because this process is reversible, the rheological properties of MR fluids are easily controlled by the magnetic field . The quick reacting properties to an external magnetic field allow MR fluids to be used for haptic devices, rotor dampers, shock absorbers in motorcycles, and power steering pumps as well as large damping systems to protect buildings and bridges from external shocks or impacts. − …”