Silica-Graphene Oxide Hybrid Composite Particles and Their Electroresponsive Characteristics

Silica-graphene oxide (Si-GO) hybrid composite particles were prepared by the hydrolysis of tetraethyl orthosilicate (TEOS) in the presence of hydrophilic GO obtained from a modified Hummers method. Scanning electron microscopy (SEM) and transmission electron microscopy (TEM) images provided visible evidence of the silica nanoparticles grafted on the surface of GO, resulting in Si-GO hybrid composite particles. Energy dispersive X-ray spectroscopy (EDX) and X-ray diffraction (XRD) spectra indicated the coexistence of silica and GO in the composite particles. The Si-GO hybrid composite particles showed better thermal stability than that of GO according to thermogravimetric analysis (TGA). The electrorheological (ER) characteristics of the Si-GO hybrid composite based ER fluid were examined further by optical microscopy and a rotational rheometer in controlled shear rate mode under various electric field strengths. Shear stress curves were fitted using both conventional Bingham model and a constitutive Cho-Choi-Jhon model. The polarizability and relaxation time of the ER fluid from dielectric spectra measured using an LCR meter showed a good correlation with its ER characteristics

Magnetorheology of Core–Shell Structured Carbonyl Iron/Polystyrene Foam Microparticles Suspension with Enhanced Stability

The sedimentation stability of a carbonyl iron (CI)-based magnetorheological (MR) fluid was improved by wrapping CI particles with a polystyrene (PS) foam layer. The PS layer on the CI particles was synthesized via conventional dispersion polymerization and was subsequently foamed using a supercritical carbon dioxide fluid to produce core–shell structured particles. The density of particles decreased after the PS-layer wrapping and subsequent PS-layer foaming. The surface morphology was observed by scanning electron microscope (SEM) and the specific surface areas were determined by Brunauer–Emmett–Teller (BET) adsorption measurements. Both modifications (PS-layer wrapping and foaming) increased the surface roughness of the particles, yet preserved particle’s spherical shape. The effect of the volume expansion after modification on the magnetorheological properties was investigated by using a vibrating sample magnetometer (VSM) and a rotational rheometer. All suspensions tested presented similar MR behaviors with the only difference in their yield stress strengths. Finally, the sedimentation properties of the synthesized particles was examined using a Turbiscan apparatus. MR fluids containing the newly developed CI particles wrapped with the foamed PS layer exhibited remarkably improved stability against sedimentation due to the reduced mismatch in density between the particles and the carrier medium

Electrorheology of Graphene Oxide

Novel polarizable graphene oxide (GO) particles with oxidized groups on their edge and basal planes were prepared by a modified Hummers method, and their electro-responsive electrorheological (ER) characteristics when dispersed in silicone oil were examined with and without an electric field applied. The fibrillation phenomenon of this GO-based electro-responsive fluid was also observed via an optical microscope under an applied electric field. Both flow curves and dielectric spectra of the ER fluid were measured using a rotational rheometer and a LCR meter, respectively. Its viscoelastic properties of both storage and loss moduli were also examined using a vertical oscillation rheometer equipped with a high voltage generator, finding that the GO-based smart ER system behaves as a viscoelastic material under an applied electric field

Magnetorheology of a Carbonyliron Microsphere Suspension with a Halloysite Additive and Its Damping Force Characteristics

A carbonyliron (CI)-based magnetorheological (MR) suspension was prepared with halloysite nanoclay particles as an additive. The MR properties of the suspension were investigated using a rotational rheometer with a parallel-plate geometry equipped with a magnetic field supply under a range of external magnetic field strengths. From the sedimentation ratio test to assess the dispersion stability, the addition of halloysite particles to the CI suspension was found to improve the sedimentation problem. MR fluids containing both pure CI and CI/halloysite were employed in a custom-designed MR damper, and their damping characteristics, such as the damping force as a function of time, displacement, and velocity, were examined experimentally because the vibration attenuation using mechanical damper systems is one of the main applications of MR fluids. Under the same magnetic field strength, the damping characteristics of the two MR fluids were found to be related directly to their yield stresses

Core–Shell-Structured Monodisperse Copolymer/Silica Particle Suspension and Its Electrorheological Response

Monodisperse core–shell-structured poly­(styrene-<i>co</i>-butyl acrylate-<i>co</i>-[2-(methacryloxy)­ethyl] trimethylammonium chloride)/silica (PSBM/SiO₂) nanoparticles were applied as new electrorheological (ER) materials in which the particles were dispersed in an insulating oil. These nanoparticles were prepared by the consecutive precipitation of cetyltrimethylammonium bromide and negatively charged tetraethylorthosilicate onto the cationic surfaces of PSBM colloidal particles. The successful deposition of the shell phase of the particles and their morphology was examined by transmission and scanning electron microscopy. Their ER properties were studied with a rotational rheometer under different shear modes: controlled shear rate, steady shear under constant shear rate, and creep test. The silica shell allowed the PSBM/SiO₂ particles to exhibit typical ER performance under an applied electric field. The dielectric spectra of the PSBM/SiO₂-based ER fluid were also recorded using an LCR meter, which was correlated to the ER performance of the ER fluid