Seung Hyuk Kwon

Core–shell-structured cross-linked poly(glycidyl methacrylate)-coated carbonyl iron microspheres and their magnetorheology

Poly(glycidyl methacrylate) (PGMA)-coated soft magnetic carbonyl iron (CI) particles were fabricated by cross-linking PGMA with ethylene glycol dimethacrylate. The synthesized core–shell structured CI/PGMA microspheres were characterized by scanning electron microscopy, Fourier transform infrared spectroscopy, and thermal gravimetric analysis. The CI particles were confirmed to be coated well with PGMA. A magnetorheological (MR) suspension was prepared based on the synthesized CI/PGMA particles dispersed in silicone oil and measured using a rotational rheometer at various magnetic field strengths. The sedimentation property, which was observed using a Turbiscan, indicated better settling stability than the pure CI particle-based MR suspension.

Monodisperse poly(2-methylaniline) coated polystyrene core–shell microspheres fabricated by controlled releasing process and their electrorheological stimuli-response under electric fields

A core-shell structured electro-responsive electrorheological (ER) particle system comprised of monodisperse poly(2-methylaniline)-coated polystyrene (PS/PMAN) microspheres was fabricated by applying a controlled swelling-releasing technique to pre-fabricated micron-sized PS seeds using a dispersion polymerization method. Compact wrapping of the PS microparticles with semiconducting PMAN without a de-doping process was examined by scanning electron microscopy and transmission electron microscopy. Fourier-transform infrared spectroscopy and thermogravimetric analysis also confirmed the chemical composition and thermal stability of the particles, respectively. Rheological characteristics of the PS/PMAN microsphere based ER fluid dispersed in silicone oil at various electric field strengths revealed a typical ER response under both steady shear flow and dynamic oscillation, demonstrating its mechanism of a conductivity model with a slope of 1.5.

Effect of surface treatment on magnetorheological characteristics of core-shell structured soft magnetic carbonyl iron particles

Core-shell structured soft magnetic carbonyl iron (CI) particles coated with poly(glycidyl methacrylate) were fabricated using a dispersion polymerization method. The surface of the CI particles was pretreated with 4-aminobenzoic acid to enhance the affinity between CI and poly(glycidyl methacrylate) (PGMA). The synthesized CI/PGMA core-shell particles were characterized by scanning electron microscopy, energy-dispersive X-ray spectroscopy, Fourier transform infrared spectroscopy, and vibrating sample magnetometry. The CI/PGMA particles were dispersed into a non-magnetic liquid for applications as a magnetorheological (MR) fluid, in which the rheological properties can be altered significantly by an external magnetic field. The MR suspension was analyzed using a rotational rheometer at various magnetic field strengths. Although the fabricated CI particles exhibited lower MR properties than pure CI particles, they showed improved dispersion stability according to the Turbiscan apparatus.

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.

Electric Field-Responsive Mesoporous Suspensions: A Review

This paper briefly reviews the fabrication and electrorheological (ER) characteristics of mesoporous materials and their nanocomposites with conducting polymers under an applied electric field when dispersed in an insulating liquid. Smart fluids of electrically-polarizable particles exhibit a reversible and tunable phase transition from a liquid-like to solid-like state in response to an external electric field of various strengths, and have potential applications in a variety of active control systems. The ER properties of these mesoporous suspensions are explained further according to their dielectric spectra in terms of the flow curve, dynamic moduli, and yield stress.

Polymeric Nanoparticle-Coated Pickering Emulsion-Synthesized Conducting Polyaniline Hybrid Particles and Their Electrorheological Study

To produce an electric stimuli-responsive electrorheological (ER) material, semiconducting core/shell-type polyaniline (PANI) hybrid particles were fabricated through Pickering emulsion-type polymerization, using poly(divinylbenzene-alt-maleic anhydride) (PDVMA) particles as a solid surfactant. The PDVMA nanoparticles were initially polymerized using a self-stable precipitation method. The fabricated PANI/PDVMA composite particles were subjected to various chemical characterizations; further, they were suspended in silicone oil at 10 vol % to prepare an ER fluid, and their viscoelastic behaviors were scrutinized using a rheometer under various input electric fields. We also adopted an LCR meter to evaluate its dielectric characteristics. Our results showed that the PANI/PDVMA composite particles display typical ER performance, such that both dynamic and elastic yield stresses follow a polarization mechanism with a slope of 2.0.

Electrorheological response of microporous covalent triazine-based polymeric particles

Microporous covalent triazine-based polymer (MCTP) particles were synthesized via a Friedel–Crafts reaction catalyzed by AlCl3, and their morphology and textural properties were confirmed by scanning electron microscopy and N2 adsorption isotherms, respectively. Electrorheological (ER) behavior of the MCTP particle-based ER fluid dispersed in silicone oil at a volume fraction of 5% was examined using a rotational rheometer to examine its viscoelastic properties such as shear stress, shear viscosity, yield stress, and dynamic moduli. Typical ER characteristics showed an increase with increased applied electric field strength following a polarization mechanism with the slope of 2 of the electric field-dependent yield stress, highlighting MCTP as a potential ER material. The dielectric spectra were also correlated with its ER effects using an LCR meter.

Magnetorheological properties and polishing characteristics of silica-coated carbonyl iron magnetorheological fluid:

While magnetorheological fluids can be used for ultra-precise polishing, for example, of advanced optical components, oxidation of metallic particles in water-based magnetorheological fluids causes irregular polishing behavior. In this study, carbonyl iron microspheres were initially coated with silica to prevent oxidation and were used to polish BK7 glass. In addition, their rheological and sedimentation characterizations were investigated. Material removal and surface roughness were analyzed to investigate the surface quality and optimal experimental conditions of polishing wheel speed and magnetic field intensity. The maximum material removal was 0.95 µm at 95.52 kA/m magnetic field intensity and 1854 mm/s wheel speed. A very fine surface roughness of 0.87 nm was achieved using the silica-coated magnetorheological fluid at 47.76 kA/m magnetic field intensity and 1854 mm/s wheel speed.

Stimuli-Responsive Polymer-Clay Nanocomposites under Electric Fields

This short Feature Article reviews electric stimuli-responsive polymer/clay nanocomposites with respect to their fabrication, physical characteristics and electrorheological (ER) behaviors under applied electric fields when dispersed in oil. Their structural characteristics, morphological features and thermal degradation behavior were examined by X-ray diffraction pattern, scanning electron microscopy and transmission electron microscopy, and thermogravimetric analysis, respectively. Particular focus is given to the electro-responsive ER characteristics of the polymer/clay nanocomposites in terms of the yield stress and viscoelastic properties along with their applications.

Magnetic Particle Filled Elastomeric Hybrid Composites and Their Magnetorheological Response

The magnetorheological (MR) elastomer as a hard and soft hybrid functional material, a composite material consisting of magnetic hard particles embedded in elastomeric soft matrix, is a branch of MR materials that are functional smart materials rapidly responding to external magnetic fields. These tunable properties of MR elastomers facilitate a variety of applications. In this brief review paper, in addition to general information on the MR elastomers, recent research not only on a wide variety of MR elastomeric systems focusing on various magnetic particles, elastomeric matrices, additives and particle modification methods, but also on their characteristics including MR properties from dynamic oscillation tests is covered along with their mechanical properties such as the Payne effect, tensile strength and engineering applications.