Enhancing the performance of electrorheological fluids by structure design

The electrorheology of electrorheological (ER) fluids based on zeolite and silicone oil under dc fields was investigated at room temperature. ER fluids with volume fractions of 27% and 30% were prepared and tested. When a 5 kV/mm dc field was applied, shear yield stress of 26.7 kPa was obtained for the latter. The ER fluid with a higher volume fraction of zeolite had a higher current density and a higher shear yield stress under the same electric field. Compared with other ER fluids based on zeolite particles with low shear yield stress, the zeolite employed by us was found to have high dielectric constant and conductivity. The high permittivity mismatch and the high conductivity mismatch of the components of the fluids were considered responsible for the high shear yield stress.

The flow properties of electrorheological (ER) fluids change with the application of an electric field. Presently, these materials are a novelty with few direct applications, but they have drawn considerable interest. Proposed applications include lubricants, dampers, clutches, brakes, etc. Existing ER fluids are best described by the Bingham fluid model. The Bingham material is described by two parameters, a yield shear stress and a viscosity. When the shear stress magnitude exceeds the yield shear stress, quasi-Newtonian flow results; otherwise the material is rigid. For many ER fluids, the yield shear stress is proportional to the square of the applied electric field. In the present study, the Bingham model is applied to a rectangular flow channel. A rigid core forms midway across the film, the core thickness being proportional to the yield shear stress. The damper force is predicted as a function of a dimensionless parameter which depends on the yield shear stress, the flow rate, and channel geometry. Calculations are performed for a simple vibration isolation system. Such a system may represent a smart shock absorber to minimize vibration response to oscillation input from a bumpy road. The ER damper is shown to be effective in isolating vibration within a band of linear behavior.

Preparation and electrorheological property of rare earth modified amorphous Ba xSr 1− xTiO 3 gel electrorheological fluid

Electrorheological (ER) fluids are considered as a type of smart fluids because their rheological characteristics can be altered through an electric field. The discovery of giant ER effect revived the researchers' interest in the ER technological area. However, the poor stability including the insufficient dynamic shear stress, the large leakage current density, and the sedimentation tendency still hinders their practical applications. Herein, we report a facile and scalable coprecipitation method for synthesizing surfactant-free tin titanyl oxalate (TTO) particles with tremella-like wrinkly microstructure (W-TTO). The W-TTO-based ER fluids exhibit enhanced ER activity compared to that of the pristine TTO because of the improved wettability between W-TTO and the silicone oil. In addition, the static yield stress and leakage current of W-TTO ER fluids also show a fine time stability during the 30 day tests. More importantly, the dynamic shear stress of W-TTO ER fluids can remain stable throughout the shear rate range, which is valuable for their use in engineering applications. The results in this work provided a promising strategy to solving the long-standing problem of ER fluid stability. Moreover, this convenient route of synthesis may be considered a green approach for the mass production of giant ER materials.

Enhanced electrorheological effectiveness and temperature effect of suspensions based on poly(ionic liquid)s neutralized with mixed counterions

Poly(diphenylamine)/polyaniline core/shell composite nanospheres synthesized using a reactive surfactant and their electrorheology

Synthesis and electrical response of polyaniline/poly(styrene sulfonate)-coated silica spheres prepared by seed-coating method

Highly substituted potato starch phosphate (HPSP) particles were synthesized via an esterification process of potato starch with a mixture of several different concentrations of disodium hydrogen phosphate and sodium hydrogen phosphate. These particles were characterized via thermogravimetric analysis, scanning electron microscope, and inductively coupled plasma mass spectrometer. The electrorheological (ER) fluid was prepared by dispersing these HPSP particles in nonconducting silicone oil, and their ER properties were investigated. The HPSP particle-based ER fluid exhibited typical ER responses with a nonzero yield stress under an applied electric field. We examined the yield stresses for the potato starch-based anhydrous ER system by varying the degree of phosphate substitution and found that the higher polarization induced by the external electric field strength resulted in the higher values of yield stresses and shear stresses.

Electrorheological (ER) fluid is a type of smart fluid whose shear yield stress relies on the external electrical field strength. The transition of ER fluid microstructure driven by the electrical field is the reason why viscosity changes. Experimentally, the transparent electrodes are used to investigate the column size distribution where an external electric field is applied to a colloidal suspension, i.e., ER fluid is increased. The coarsening profile of ER suspensions is strongly related to electrical field strength, but it is insensitive to particle size. In addition, in a low field range the shear stress corresponding to the mean column diameter is studied and they are found to satisfy a power law. However, this dependence is invalid when the field strength surpasses a threshold value.

A method for simulating electrorheological (ER) fluids is developed using LAMMPS (large-scale atomic, molecular massively parallel simulator) molecular dynamics simulations, aiming to model and analyze the microstructure and rheological behavior of ER fluids under an electric field. The results demonstrate that our simulation accurately captures the microstructural changes in ER fluids, and the simulation data show an impressively high level of consistency when compared directly with experimental data. The main innovation lies in our simultaneous consideration of dipole interactions, harmonic effects of ER particles, and the contact effect of electrode plates. The contact effect model is demonstrated in detail in our simulations of the chain formation process and the shear process of ER particles in ER fluids, accompanied by corresponding experimental comparisons. Our simulations provide insights into the microscopic mechanisms of ER fluids and establish a theoretical foundation for the development of smart materials and rheological devices.

Polar molecule dominated electrorheological (ER) fluid is a new type of ER material with high shear stress. The alignment of polar molecules adsorbed on the dielectric particles in the direction of the high local field between the particles plays a decisive role in such new ER fluids. In measuring the current density of ER fluid composed of Ca—Ti—O particles, it was found that the conductive behavior of the fluid exhibits Poole-Frenkel character, which is one of the particular features for polar molecule dominated electrorheological fluids. By heating the Ca—Ti—O particles at 500 ℃ to remove the polar molecules adsorbed on the particles, however, the current density of ER fluid fabricated with pure Ca—Ti—O particles has linear dependence on the electric field approximately, same as in the traditional ER fluids.

Preparation of high performance electrorheological fluids with coke-like particles from FCC slurry conversion

Ionic liquid-based organically modified silica for the development of new electrorheological fluids

One-pot synthesis of polyaniline-doped in mesoporous TiO 2 and its electrorheological behavior

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.