Core–Shell Structured Magnetite-Poly(diphenylamine) Microspheres and Their Tunable Dual Response under Magnetic and Electric Fields

Abstract

Core−shell type poly(diphenylamine)-coated magnetite (Fe 3 O 4 −PDPA) microspheres were designed and adopted as a novel actively tunable smart material which is responsive under both electric and magnetic fields. Their morphology, chemical structure, crystalline structure, and thermal properties were characterized using scanning electron microscopy, transmission electron microscope, Fourier transform-infrared spectroscopy, Xray diffraction, and a thermal gravimetric analyzer. Their magnetic and dielectric properties were determined using vibrating-sample magnetometer and an LCR meter, respectively. They were dispersed in silicone oil and their electrorheological (ER) and magnetorheological (MR) responses under the electric and magnetic fields, respectively, were examined. The formation of chain structure of Fe 3 O 4 −PDPA based E/MR fluid under the application of electric field or magnetic field was observed by an optical microscopy and the sedimentation stability was observed by a Turbiscan optical analyzer system. It was observed that the yield stress, ER efficiency, and leakage current density increased with an increase in the particle concentration, while the slope of the electric field-dependent yield stress decreased. Several models such as the Bingham model, Herschel−Bulkley model, and Cho− Choi−Jhon equations were used to describe the shear stress curves of the ER fluid; the curves fitted well. For the dielectric properties, the two types of ER fluids tested displayed the same relaxation time and distribution; however, the one with the higher concentration had a higher dielectric constant and polarizability. The Fe 3 O 4 −PDPA based MR fluid (10 vol %) exhibited typical MR properties. In addition, the Herschel−Bulkley model matched well with the shear stress curves under a magnetic field.

Effect of polydispersity in concentrated magnetorheological fluids

“…This index measures the colloidal stability of dispersions and emulsions through transmitted or backscattered infrared light (λ = 850 nm) [78]. Many authors have already used this type of analysis to assess the stability of MR fluids against sedimentation, such as Kim and Choi [79], Dong et al [80], Cvek et al [81].…”

The influence of synthesis conditions on the electrorheological performance of iron(II) oxalate rod-like particles

“…The controlled variation in reaction conditions led to the preparation of particles with different sizes and morphologies, aiming to optimize the particles' preparation to achieve the highest ER effect possible. In addition, the particles synthetized by this one-step method exhibit improved ER performance in comparison to the recently published ER materials [35]. The iron(II) oxalate particles possessing rod-like morphology appear to be suitable for practical applications in electrorheology.…”

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

“…Covering the surface of Fe 3 O 4 particles with organic polymers could help overcoming the problem of Fe 2+ being oxidized [ 39 , 40 ], and make Fe 3 O 4 particles have better dispersion stability in ER fluids [ 41 , 42 ]. In particular, coating with conducting polymers can produce composite particles with conductive shell/magnetic core structures that can be used not only for MR, but also for ER suspensions [ 43 , 44 ].…”