Electrorheological Effect In Suspensions Research Articles

Electrorheological effect of suspensions containing mixed size of poly(ionic liquid) microspheres

In this paper, the electrorheological (ER) effect of suspensions containing mixed size of poly(ionic liquid) (PIL) microspheres were studied by combining experiment and molecular dynamics simulation. The PIL microspheres with two particle sizes were prepared via a cooling-assisted phase separation method. The PIL microspheres were dispersed in silicone oil to form five kinds of suspensions with different volume ratios of large and small at a fixed particle volume fraction. The ER effect of these suspensions was measured by a rheometer. We established ER suspension models for five suspensions and simulated the rheological curves of the ER suspensions using molecular dynamics-stochastic rotation dynamics method. Both experiment and simulation results showed that the ER effect of suspensions containing mixed size of PIL microspheres was lower than that of suspensions containing uniform size of PIL microspheres. The reasons for the influence of mixed particle size on ER effect were analyzed through the three-dimensional visualization simulation results.

High electrorheological effect in Bi1.8Fe1.2SbO7 suspensions

We report on the first experimental evidence of the electrorheological effect in suspensions of superfine pyrochlore-type Bi1.8Fe1.2SbO7 powders. Tensile-compressive and shear stress studies of the electrorheological fluids, with various filler contents, revealed an exceptionally high electrorheological effect in the materials – the tensile yield strength at 5kV/mm reached about 20kPa. The frequency dependencies of dielectric permittivity, dielectric loss tangent, and the conductivity of the suspensions with various filler contents allowed estimation of the dielectric permittivity values for superfine Bi1.8Fe1.2SbO7 particles at zero and infinite frequencies. The study reveals new oxide materials as promising fillers for electrorheological fluids.

Comparative study of the electrorheological effect in suspensions of needle-like and isotropic cerium dioxide nanoparticles

A novel approach to the analysis of the electrorheological effect is proposed, based on the expansion of dimensionless relative shear stress as function of electric field strength in the power series $$ {\tau}_{\mathrm{rel}}=\frac{\tau_E}{\tau }=1+\frac{\alpha }{\tau }E+\frac{\beta }{\tau }{E}^n $$ . The application of this approach to investigation of the electrorheological effect in suspensions of isotropic and needle-like CeO2 nanoparticles in polydimethylsiloxane has revealed that the polynomial coefficients can be judged as a measure of the efficiency of transformation of electrical energy into mechanical energy. The values of α and β coefficients depend on the shape and concentration of filler particles, as well as on the shear rate. The value and the sign of these coefficients determine both the magnitude of the electrorheological effect and the type of dependence of the shear stress (linear or power law) on the strength of the electric field. It has been shown that the values of α and β coefficients for the electrorheological fluids with needle-like particles are greater than for fluids with isotropic particles (at the same concentration of suspensions), which is associated with the different polarization of particles in the applied electric field.

Comparative parameters of the electrorheological effect in suspensions of nanosized barium titanyl acetates and titanyl oxalates in PMS-20 silicon oil

The regularities of the effect of intensities of dc and ac electric fields (50 Hz frequency) on dielectric and electrorheological parameters of electrorheological fluids based on PMS-20 silicon oil with nanosized fillers, barium titanyl acetate and titanyl oxalate, are revealed.

The dielectric spectrum and the electrorheological effect in suspensions of varying conductivity: Part 2. Modeling of the electrorheological effect

In this part, attention is given to the electrorheological effect of suspensions of polarizable particles in three different liquids of varying conductivity. The electrorheological properties of the suspensions are analyzed with a kinetic model that describes the flow-induced modification of the structures formed by the particles under dc electric fields. Under quiescent conditions, the model describes the variation of viscosity of the suspension with the electric field and particle concentration, as well as the change in the yield stress with electric field. The effect of non-linear conductivity is introduced in the model to account for the trend towards saturation observed in the viscosity at high electric fields and particle concentration. Furthermore, the contribution of non-linear conduction in the model allows the prediction of the yield stress at high electric fields. The model further describes the variation of viscosity with shear rate under a given electric field, and time-dependent phenomena arising from the dynamics of the breakage-reformation process of the structures.

Study of electrorheological sensitivity of suspensions based on hydrated aluminum oxides

The electrorheological fluids with the disperse phase formed by the particles of hydrated aluminum oxides prepared by the chemical precipitation from aluminum-containing solutions and subjected to heat treatment at different temperatures are studied. It is shown that the electrorheological activity of suspensions depends on the chemical and phase compositions of the dispersed phase. The influence of water, whose different forms comprise hydrated aluminum oxides, on the manifestation of the electrorheological effect of suspensions is estimated. It is established that the maximum gain in the effective viscosity of electrorheological fluids is related with water molecules forming hydrogen bonds in the interlayer space of the boehmite lattice.

The dielectric spectrum and the electrorheological effect in suspensions of varying conductivity: Part 1. Modeling of the dielectric spectrum

The dielectric behavior of electrorheological (ER) suspensions composed of non-colloidal silica gel particles of irregular shape and liquids with varying conductivity is examined in this work. The dielectric properties of the suspensions are analyzed in the diluted and semi-concentrated regimes at different frequencies maintaining the electric field constant. Primarily, the dielectric behavior is studied with particular attention to the dependence of the dielectric relaxation process on particle concentration and their relation with the conductive behavior. The dielectric spectrum is analyzed with Maxwell–Wagner interfacial polarization model in the low frequency region and with the Debye model at moderate frequencies. A non-localized diffusion process (or ideal conduction) is considered to analyze the dielectric spectrum in more conductive suspensions. Since a strong correlation exists between the ER activity of a suspension and its dielectric spectrum, the modeling of the dielectric spectrum provides understanding of the polarization processes which induce the ER effect studied in Part 2.

Study of electrorheological properties of poly(p-phenylene) dispersions

Samples of powdered poly(p-phenylene) lightly doped with ferric chloride were dispersed in silicone oil and the observed electrorheological (ER) effect was studied. The conjugated polymers were obtained in three different synthetic procedures resulting in materials of different crystallinity, which was then additionally modified by annealing in vacuum. The polymer samples were carefully characterized and their electric conductivity and permittivity, doping level, x-ray diffractograms, Fourier-transform infrared spectra, and grain size distribution were determined. The influence of these properties on the magnitude of the ER phenomenon was examined. It was found that the ER activity of the suspensions depended strongly on the crystallinity of a dispersed polymer. This observation was correlated with the ionic conductivity of the material leading to the conclusion that the ER effect in suspensions of FeCl3 doped polyphenylene resulted from bulk polarization processes relying on movement of ions within the polymer matrix. The electronic conductivity typical of doped conjugated polymers contributed predominantly to increase of current flowing through an ER suspension under electric field and not to the ER effect itself.

Electrorheological effect in suspensions of polyaniline

The electrorheological (ER) effect relies on the increase of viscosity of a fluid under electric field. The studied ER fluids (ERFs) were prepared out of silicone oil and polyaniline lightly protonated with four different acids of pKa values from −8 to +1.8. Rheological properties of the ERFs were measured under electric field up to 2.3 kV/mm. The influence of the protonation level of polyaniline and the acid used on the magnitude of the ER effect was studied. We propose an explanation of the observed relations based on measurements of dielectric properties of the polymers. The strongest ER effect was observed for polyaniline samples whose relaxation frequency was about 8 kHz, supporting the idea that the relatively slow polarisation processes were responsible for the ER effect. In addition, it was demonstrated that conductivity and dielectric constant of the polymers depended on the strength of the acids applied.

Electrorheological effect in suspensions of conductive polymers

Electrorheological (ER) effect relies on increase of viscosity of a fluid under electric field. In the present study electrorheological fluids (ERFs) were prepared out of FeCl 3 doped poly( p-phenylene) and silicone oil. Rheological properties of the ERFs were measured under electric field up to 2.2 kV/mm. Influence of electric field and composition of the fluids on magnitude of the ER effect were studied. It was found that the ER effect is observed in ERFs containing amorphous polymer and not a semi-crystalline one. This has been attributed to ionic contribution of conductivity in the amorphous polymer which is not present in the crystalline material.