[en] Graphene oxide (GO)/poly(2-methylaniline) (P2MAN) composite particles were prepared by chemical oxidation polymerization and adopted as an electrorheological (ER) material. Because of its electrical conductivity originating from both semi-conducting P2MAN and GO, it could be tuned finely using P2MAN for ER applications. The morphology and chemical structure of the composite were examined by scanning electron microscopy, Fourier transform infrared spectroscopy and X-ray diffraction. The ER properties of the GO/P2MAN composite particles dispersed in silicone oil were examined with and without an applied electric field. The fibrillation phenomenon of this GO/P2MAN-based electro-responsive fluid was also observed by optical microscopy under an electric field. The flow curves and dynamic modulus of the GO/P2MAN suspension were measured by rotational rheometry under a range of electric field strengths, exhibiting typical ER characteristics and a slope of the dynamic yield stress of 1.5. GO appeared to improve the compatibility of the composite particles within the medium, which resulted in improved sedimentation stability compared to that of the P2MAN-based ER fluid. - Highlights: • GO/P2MAN composite was fabricated by Hummers method and oxidation polymerization. • The composite particles based fluid exhibited typical electrorheological properties. • The fluid was correlated to conduction model and showed solid-like characters. • GO was helpful to improve stability of fluid due to large surface area and compatibility

[en] Graphical abstract: - Highlights: • GO-based PANI, NCOPA and PS nanocomposites are prepared. • The nanocomposites are adopted as novel electrorheological (ER) candidates. • Their critical ER characteristics and dielectric performance are analyzed. • Typical ER behavior widens applications of GO-based nanocomposites. - Abstract: Graphene oxide (GO), a novel one-atom carbon system, has become one of the most interesting materials recently due to its unique physical and chemical properties in addition to graphene. This article briefly reviews a recent progress of the fabrication of GO-based polyaniline, ionic N-substituted copolyaniline and polystyrene nanocomposites. The critical electrorheological characteristics such as flow response and yield stress from rheological measurement, relaxation time and achievable polarizability from dielectric analysis are also analyzed

[en] Inorganic black particles (Black 444) were modified with poly(methyl methacrylate) as a shell material by using dispersion polymerization to improve their dispersion stability in a medium oil for electrophoretic display applications. They were also positively charged with vinylimidazole to enhance their electrophoretic mobility. The morphology and the shape of the composite particles were characterized by using scanning electron microscopy. The thermal properties and the chemical structure of the samples were examined by using thermogravimetric analysis and Fourier transform infrared spectroscopy, respectively. In addition, the electrophoretic mobility and the zeta-potential of the black444 /PMMA /vinylimidazole particles in a dielectric fluid were measured by using optical microscopy and electrophoretic light scattering. With increasing positive charge, the black444 /PMMA /vinylimidazole particles showed improved electrophoretic characteristics compared to pristine Black 444.

[en] Conducting poly(aniline-co-diphenylamine) (PANI-PDPA) nanoparticles were fabricated via chemical oxidative polymerization in an emulsified system as a novel electrorheological (ER) material. A polymerizable surfactant and an amphiphile, which act as both an emulsion stabilizer and a polymerizable monomer, were employed. Morphological and compositional analyses revealed that monodispersed spherical copolymeric nanoparticles were successfully obtained under controlled conditions. The rheological behaviors of the PANI-PDPA-based ER suspension were evaluated by carrying out its rotating shear test under various electric field strengths, in which its stress behaviors were qualitatively analyzed using a four-parametric model.

[en] In this work, silica/poly(o-anisidine) (POA) core–shell structured microspheres were synthesized by coating the silica core surface with POA with a help of a chemical grafting agent, N-[(3-trimethoxylsilyl)-propyl] aniline. The synthesized silica microspheres were then applied as a polymer/inorganic composite particle-based electrorheological (ER) fluid. The morphology of the silica/POA microspheres was examined by using both transmission electron microscopy and scanning electron microscopy, while their thermal properties and chemical structure were checked by thermogravimetric analysis and Fourier-transform infrared spectroscopy, respectively. The ER properties of the silica/POA particle-based ER fluid were examined by using a Couette-type rotational rheometer equipped with a high-voltage power supplier and analyzed by the Bingham model and modified Mason number. In order to obtain additional information about the electrical polarization properties, the dielectric spectra were measured by an LCR meter and fitted by using the Cole–Cole equation. Furthermore, suspension stability of the ER fluid was tested using Turbiscan. (paper)

[en] Monodisperse semiconducting poly(N-methylaniline) (PNMA) microspheres with a suitable electrical conductivity were fabricated using a chemical oxidation process and employed in an electrorheological (ER) suspension. Morphological image of the synthesized PNMA microsphere was assessed via scanning electron microscope and transmission electron microscope. Its chemical composition and thermal behavior were determined using Fourier-transform infrared and thermal gravimetric analysis, respectively. Chain-like structure formation under an input electric field in ER fluid containing silicone oil and 10 wt% PNMA microspheres was observed directly with optical microscopy. Viscoelastic characteristics of the ER fluid under an input electric field were evaluated with a rotational rheometer. Yield stress with a power exponent of 1.5 was observed, along with typical solid-like property under electric field. Dielectric behavior of the ER suspension measured was also found to be closely associated with its ER behavior. (paper)

[en] Highly magnetic Fe₃O₄ nanoparticles with a hollow spherical shape were fabricated via a solvothermal technique and were introduced into soft-magnetic carbonyl iron (CI)-based magnetorheological (MR) fluid to enhance the stability and its MR properties. The structural behaviors and magnetic characteristics of hollow Fe₃O₄, pure CI, and the hollow Fe₃O₄/CI mixture were demonstrated by scanning electron microscope, transmission electron microscope, and vibrating sample magnetometry. The MR properties of the systems with and without the hollow Fe₃O₄ additive were examined by controlled shear rate and oscillatory tests using a rotation-rheometer. The Herschel–Bulkley equation provided an adequate fit for the flow curve, and all of the yield stresses followed the universal scaling equation. The suspension characteristics of the two MR systems were further examined using a Turbiscan device. The CI-based MR fluid with hollow Fe₃O₄ additive was observed to exhibit higher yield stress as well as improved dispersion than does the pristine CI-based MR fluid, demonstrating that the performance of CI-based MR fluids can be further optimized by using additives. (paper)

[en] Carbonyl iron (CI) based magnetorheological (MR) fluid exhibits serious dispersion defect in general due to large density mismatch between CI particles and continuous medium, which restricts further MR application. Thus, various strategies were explored either to reduce the density or to prevent CI particle aggregation. Among them, polymer coating technology becomes more prevalent due to favorable morphology obtained and effective decrease in density by introducing polymeric shell; nevertheless, coating polymer on the surface of CI particles is always influenced by the selected grafting agent, mole ratio of reactant or the temperature of reaction. In this work, considering self-assembling trend of carbon nanotube (CNT) which exhibits similar density with polymer but better magnetic property due to the iron catalyst, we constructed a dense nest composed of CNT on the surface of CI particles by using 4-aminobenzoic acid (PABA) as a grafting agent under sonication. Thickness and morphology of the CNT nest were found to be related with sonication duration via SEM/TEM images. MR performances (yield stress behavior, shear viscosity) of the CI/CNT particles based MR fluid were investigated via controlled shear rate and controlled shear stress methods. Finally, sedimentation observation was checked to be improved.

[en] The core–shell structured snowman-like (SL) microparticles coated by functionalized multi-walled carbon nanotube (MWNT) were prepared in the presence of different surfactants including cationic surfactant-cetyl trimethylammonium bromide (CTAB) and anionic surfactant-sodium lauryl sulfate (SDS). The effect of surfactants on adsorption onto SL particles was characterized by scanning electron microscopy (SEM), thermogravimetric analysis (TGA) and conductivity. The cationic surfactant is found to be more effective than anionic surfactant for helping nanotube adsorbed onto microparticle due to the presence of electrostatic interaction between the functionalized MWNT and the surfactant. Furthermore, the MWNT/SL particles dispersed in silicone oil exhibited a typical fibril structure of the electrorheological characteristics under an applied electric field observed by an optical microscope (OM), in which the state of nanotubes wrapped on the particles strongly affects their electro-responsive characteristics.

[en] The electrorheology (ER) of suspensions based on polystyrene/polyaniline (PS/PANI) core/shell structured microspheres and those based on disk-like zeolite particles at different electric fields and particle volume fractions have been studied, respectively. Both types of ER fluids showed abrupt shear thickening under high electric fields and low shear rates, as well as shear thinning when the shear rate increased. A normalized method that considers the effects of electric field strength, shear rate and particle volume fraction was proposed to compare the rheological curves of the two ER fluids. The curves evaluated from the normalization method showed similar shear thinning at low shear rates and the hydrodynamic effect at high shear rates. Shear thinning represents the structure destroyed by shearing, and shear thickening at low shear regions indicates the dramatic structure change. The particle volume fraction and structure factor effects demonstrate that the mechanical contact between particles and the wall of the electrodes is crucial to the shear strength of ER fluids, indicating an electric/magnetic field modulated friction mechanism of the ER and magnetorheological (MR) effects. (paper)