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The ground state symmetry of an electrorheological fluid is studied numerically using a finite element method. The free energies of body-centered cubic, body-centered tetragonal, simple hexagonal, hexagonal close-packed, simple cubic, simple hexagonal, and honeycomb structures are calculated for systems containing homogeneous particles with the dielectric constant greater or smaller than that of the base fluid. In accordance with other studies, the body-centered tetragonal symmetry was found to be the most favored lattice symmetry. The ground state of an ER system containing two types of particles, i.e., particles with the dielectric constant greater and smaller than that of the base fluid, was found to consist of separated particle columns each of which has only one type of particles. These separated particle columns preferred body-centered tetragonal symmetry. However, simple hexagonal and honeycomb symmetries were found to be energetically quite close to a body-centered tetragonal symmetry. In addition, simple hexagonal and honeycomb symmetries do not need phase separation between different types of particles and are thus more likely to form. Dynamical effects were studied using a point dipole model. Within the time-span studied the system seemed to form a polycrystalline structure.

We study model electrorheological (ER) fluids which consist of three material components in an attempt to explain recent experimental results, in which the ER effects can be promoted by adding some water. At low water concentration, the droplets tend to aggregate on the surfaces of the dispersed particles, forming coated microspheres. The ER effects are analyzed via spectral representation, and the experimental conditions for optimal ER responses are obtained. At low frequencies, it is found that by tuning the thickness and dielectric properties of the coating materials, it is possible to enhance the effective dielectric constant, thereby increasing the applicability of the ER fluids.

The electrorheological (ER) properties were studied with ternary suspensions containing solid and liquid dispersoids in silicone oil (DMS). The solid dispersoid used was polyether/montmorillonite nanocomposite particles in which polyether molecules were intercalated between the layers of montmorillonite. The liquid dispersoid was urethane-modified polyether prepared from 4,4′-diphenylmethane diisocyanate (MDI) and poly(propylene glycol) (PPG). The steady shear viscosity and dynamic viscoelasticity were measured with a rotating parallel disc rheometer equipped with ER measurement system. The binary and ternary mixtures of these solid and liquid dispersoids with DMS, i.e. composite particle/DMS suspension, polyether/DMS liquid blend, and ternary blend containing both dispersoids, showed an increase of viscosity in response to an electric field (positive ER effect). The ER effect of a ternary suspension containing the particles and polyether liquids was larger than those of binary suspension or blend with one of these dispersoids. The ER effect was found to be improved by combination of the solid and liquid dispersoids, although the recovery time of viscosity after removing the electric field became rather longer, which would be due to the partly irreversible macroscopic aggregation of the dispersoids.

ER fluids under shear are often approximated by the Bingham model with the electric field induced yield stress. This approach, however, neglects the properties of the solid phase created. The oscillation measurements taken under field below the yield point and leading to calculation of storage and loss moduli of the electrified solid do not allow for determination of the full stress–strain relationship of the solidified ER suspension. In order to overcome this problem and collect information about the mechanical properties of this solid a dedicated rheometer was constructed capable of measuring small strains under moderate stresses and under electric field. Full shapes of the stress–strain curves were recorded leading to determination of storage modulus, maximum deformation and yield point. Looking for relations between the viscoelastic behavior of ER suspensions and properties of their material components a series of fluids comprising silicone oil dispersions of conductive polymers (polyaniline, poly(p-phenylene), pyrolyzed polyacrylonitrile) and polymer electrolytes (polyacrylonitrile complexes with inorganic salts) was studied. It was found that the viscoelastic responses of ER fluids were affected by material characteristics of the dispersed phase.

In this study, electrorheological (ER) behaviour of silica nanocomposite suspensions treated with urea and N, N – dimethylformamide (DMF) in DC electric field has been investigated. While the ER effect of the neat silica itself was very low, the modification of silica nanoparticles improved compatibility of the solid and liquid phase and increased considerably ER activity of the system. In contrast to maximum possible concentration about 5 wt.% of neat silica due to particle aggregation 20 wt.% suspension of treated particles with low field-off viscosity could be prepared. The dielectric measurements showed that with increasing amount of urea deposited on the silica particles both the difference between the limit values of the relative permittivities and the relaxation frequency increased. This indicates a great influence of both particle polarizability and the rate of rearrangement of the ER structure in the electric field on the ER intensity. After DMF addition the changes in dielectric properties reflected the higher ER activity. At higher particle loading (25 wt.%) mutual particle interaction increased and field-off viscosity steeply rose. The comparison of the behavior of 20 and 25 wt.% suspensions of modified particles showed that even if high yield stress at higher particle content under electric field application sets in, its relative increase indicating the ER efficiency due to high field-off value may be much lower than at lower suspension loading.

The paper deals with the effect of two conductive polymers (polyaniline, PANI, and polypyrrole, PPy) in combination with inorganic particles on the response of silicone-oil suspensions. Conductive polymers cause a significant increase in electrorheological response. PANI combined with silica is much more efficient when in the form of a thin layer on the particle surface than if the two components are simply mixed. All combinations are followed from the viewpoint of viscosity and yield stress.

We prepared polyaniline (PANI) /multi-walled carbon nanotube (MWNT) nanocomposites of both PANI pierced MWNT nanocomposites synthesized using polyvinyl alcohol) as a polymeric stabilizer and PANI/MWNT nanocables via an in-situ oxidative polymerization directed by a cationic surfactant of cetyltrimethylammonium bromide (CTAB). In addition to chemical analysis of the products, the formation of nanocomposite nanocable and their morphology in which the MWNTs were entirely encapsulated by amorphous PANI, were confirmed by scanning electron microscopy (SEM) and transmission electron microscopy (TEM). Electrorheological (ER) fluids were prepared by dispersing both of these synthesized MWNT/PANI nanocomposites in insulating silicone oil and their ER properties were investigated by controlling applied DC electric field strengths. The synthesized nanocomposite particles have enhanced interparticle interactions, and the shear stresses increase with the electric field strength for a broad range of shear rate. Among three different constitutive equations adopted, the Cho-Choi-Jhon model was found to fit the flow curves quite well.

Encapsulated polypyrrole (PPy) with different amount in the channels of mesoporous silica (SBA-15) was synthesized. The XRD and N₂ adsorption/desorption isotherms analysis show that PPy with different loadings in the channels does not affect the ordered hexagonal structure of resultant PPy/SBA-15 nanocomposites. Further, the electrorheological (ER) properties of the nanocomposites with different PPy loadings were investigated by steady and oscillatory shear experiments. The results reveal that PPy/SBA-15 fluids exhibit typical ER and viscoelastic behavior under the applied electric field and ER response depends mainly on PPy loadings and there is an optimum PPy loading for strong ER effect.

In this paper, we study the preparation of titanate/polypyrrole core-shell rod-like composite particles. The mere titanate rod-like particles were prepared as core material and PPy was polymerized on their surface in different amounts. Rheological measurements showed that under an applied external electric field, shear stress of these materials significantly increased with amount of PPy in the shell layer. The yield stresses obtained from the Cho-Choi-Jhon model were correlated with dielectric properties of suspensions. Polarizability as a measure of particle polarization obtained from Havriliak–Negami model of dielectric spectra increases with the content of PPy in the samples. Furthermore, role of particle concentration and silicone oil viscosity was also investigated.

Electrorheology (ER) of ferroelectric materials such as nanometric BaTiO₃ is still not fully understood. In this paper, nanoparticles of Ba_xSr_(1-x)TiO₃ (where x = 0.8, 0.9 or 1.0) were synthesized using the method of Pechini, calcinated at 950°C, and after, lixiviated under pH 1 or pH 5. A controlled stress rheometer (MCR-301) was used to make the ER characterization of dispersions made of Ba_x Ti_1-xO₃ in silicone oil (30% w/w), where (a) shear stress as a function of DC electric field (under constant shear rate) or (b) shear stress as a function of shear rate (under constant AC or DC electric field) were measured. We observed that electrophoresis occurred under electric field DC, creating a concentration gradient which induced phase separation in ER fluid. On the other hand, under AC fields above 1 kV/mm, the ER effect is stronger than for DC field, and almost without electrophoresis. Furthermore, there is an AC frequency, dependent on the disperse phase, where the ER effect has a maximum.

Black carbon, a part of harmful PM2.5 air pollution, is the second largest contributor to global warming. Due to per unit of mass, black carbon has a warming impact on climate 460–1,500 times stronger than CO₂. UNEP emphasizes that the black carbon issue is more urgent than CO₂ now. Unfortunately, current technologies cannot help large factories in preventing emission of black carbon particles into air because they fail to catch them effectively. Therefore, a new technology, which can catch black carbon and other PM2.5 pollution effectively, is critically needed. Here we report that electrorheology is the solution we are looking for. Under a strong electric field, black carbon and other particles are polarized. When the polluted air flow becomes a special flow with pollution particles moving adjacent to the electrodes, black carbon and other particles are captured by the electrodes effectively. Our tests have confirmed that with this technology, more than 98% black carbon and other PM2.5 particles can be caught. Moreover, this technology is not only suitable as incoming air filters, but also appropriate for large factories in preventing emitting black carbon and pollution into air. We hope that electrorheology will improve our environment and reduce global warming effectively.

Electrorheological (ER) properties of polyaniline (PAni), pumice and polyaniline/pumice composites (PAPC) were investigated. Polyaniline and PAni/pumice composite were prepared by oxidative polymerization. PAni/pumice particles-based ER suspensions were prepared in silicone oil (SO), and their ER behavior was investigated as a function of shear rate, electric field strength, concentration and temperature. Sedimentation stabilities of suspensions were determined. It has been found that ER activity of all the suspensions increases with increasing electric field strength, concentration and decreasing shear rate. It has shown that the suspensions have a typical shear thinning non-Newtonian viscoelastic behavior. Yield stress of composite suspensions increased linearly with increasing applied electric field strength and with concentrations of the particles. The effect of high temperature on ER activity of pumice/silicone oil systems was also investigated.

The apparent viscosity of the electrorheological(ER) fluids can be changed with the variation of applied electric field strength. The damping force offered by ER shock absorbers can then be controlled by using the characteristics. It is found that, besides the performance of the ER fluids, the construction design of the shock absorber also strongly affects the characteristics of ER shock absorbers. In this paper, this phenomenon is discussed in detail with different construction styles of ER shock absorbers and mechanical analysis is done with hydro-mechanical and rheological theories.

This study was aimed on the preparation of titanate/polypyrrole core-shell rod-like composite particles. The mere titanate rod-like particles were prepared as a core material and PPy was polymerized on their surface in different amounts. Rheological measurements showed that under an applied external electric field, shear stress of these materials significantly increased with amount of PPy in the shell layer. The yield stresses obtained from the Cho-Choi-Jhon model were correlated with dielectric properties of suspensions. Polarizability as a measure of particle polarization obtained from Havriliak-Negami model of dielectric spectra increases with the content of PPy in the samples. Furthermore, role of particle concentration and silicone oil viscosity was also investigated.