Effect of Electric Field Strength and Water Content on the Electrorheology of Silica Dispersions

The effect of water content on the electrorheological effect (ERE) behaviour of silica dispersions has been investigated. The types of silica powders were fumed silica, precipitated and acid washed silica and colloidal silica. Silica dispersions with a water content varying in the range 10% - 30%, and with conducting ions deliberately added, were redispersed in chlorinated hydrocarbon oil and then the ER behaviour studied. Samples were tested on a static yield rig (SYR), an instrument which can measure both the yield stress and the conductivity. The effects of electric field strength and water content on the ERE were studied. The yield stress initially increased with increase in electric field strength and then decreased at high electric fields suggesting a breakdown in structure of the electrorheological fluid samples tested. It was also found that the ERE increased and electric saturation or electric breakdown shifted to lower electric fields as the water content increased. Higher electric fields caused a drop in the ERE.

A further investigation to mechanism of the electrorheological effect of waxy oils:Behaviors of charged particles under electric field

Exposing waxy oils to an electric field may significantly improve their cold flowability.Our previous study has shown that interfacial polarization,i.e.,charged particle accumulation on the wax particle surface,is the primary mechanism of the electrorheological behavior of waxy oils.However,the way that charged particles interact with wax particles under an electric field remains unknown.In this study,we found no viscosity and impedance change for two waxy crude oils after their exposure to a high-voltage electric field.However,the yield stresses were reduced obviously.We thus proposed that the collision of colloidal particles such as resins and asphaltenes with the wax particles could be an essential mechanism that the wax particle structure was weakened.To verify this hypothesis,a series of ad hoc experiments were carried out,i.e.,by performing electrorheological tests on model waxy oils containing additives removable under an electric field,including electrically-neutral colloidal particles(Fe3O4),charged colloidal particles(resins),and oil-soluble electrolyte(C22H14CoO4),respectively,and demonstrated that upon application of a high-voltage electric field,charged particles in a waxy oil may move and thus collide with wax particles,and consequently adhere to the wax particle surface.The particle collision results in damage to the wax particle network,and the electrostatic repulsion arising from the adhesion of the charged particle on the wax particle diminishes attraction between wax particles.This study clarifies the process of interfacial polarization.

Induced dipole dominant giant electrorheological fluid

Traditional dielectric electrorheological fluid(ER)is based on the interaction of dielectric particle polarization,and the yield stress is low,which cannot meet the application requirements.The giant ER(GER)effect is caused by orientations and interactions of polar molecules adsorbed on the particle surfaces.Despite the high yield stress,these polar molecules are prone to wear and fall off,resulting in a continuous reduction in shear stress of GER liquid,which is also not suitable for application.Here we introduce a new type of ER fluid called induced dipole dominant ER fluid(ID-ER),of which the particles contain oxygen vacancies or conductor microclusters both prepared by high energy ball milling(HEBM)technique.In the electric field E,oxygen vacancies or conductor microclusters form induced dipoles.Because the local electric field E_(loc) in the gaps between particles can be two to three orders of magnitude larger than E,the induced dipole moments must be large.The strong interactions of these induced dipoles make the yield stress of the ID-ER fluid reaching more than 100 kPa.Since there are oxygen vacancies or conductor microclusters everywhere in the particles,the particles will not lose the function due to surface wear during use.The experimental results show that the ID-ER fluid possesses the advantages of high shear stress,low current density,short response time,good temperature stability,long service life,and anti-settlement,etc.The comprehensive performance is much better than the existing ER materials,and also the preparation method is simple and easy to repeat,thus it should be a new generation of ER fluid suitable for practical applications.

Theoretical Research on Electrorheological Isolator

A new type of isolator, the electrorheology (ER) isolator, is mainly described. Through theoretical analysis, a simplified physical model is established under some hypotheses and a series of motion equations are deduced. According to the transmissibility curve simulation under different electric field strengths, the main factors influencing ER isolator’s working properties have been ascertained. Finally, it proves that ER isolator works well in both low and high frequency zones, it can decrease the force transmitted and enlarge the isolation frequency domain efficiently.

Application of Composite Ultrafine Particles in ER Fluids

Aim To obtain a kind of electrorheological (ER) flind with high comprehensive properties in order to satisfy the needs of engineering application. Methods A new type of dispersed phase── composite ultrafine particles (UFP) was obtained by the method of microemulsion, which was used to mix with silicon oil. aam electroinduced stress and apparent viscosity of the ER fluids with three different volume fractions were tested under the conditions of different temperatures, electric fields and shear rates. Results A series of systematic tests show that the new type of ER fluids with volume fraction of 30% possesses obvious ER effect. Conclusion The double layers polarization plays an important role in ER effect.

ELECTRORHEOLOGICAL PROPERTIES OF POLYANILINE/PUMICE COMPOSITE SUSPENSIONS

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 particlesbased 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 purrfice/silicone oil systems was also investigated.

Influence of the Dosage of Surfactant on the Electrorheological Behaviors of Fluids

To investigate the influence of surface characteristics of particles on electrorheological (ER) fluids, water free complex strontium titanate particles were synthesized through the sol gel technique and different mass fraction of the surfactant was doped in particles and dispersed in silicon oil. The test shows that surface characteristics of particles have great influence on the behavior of ER fluids. Surface tension, surface polarity and interfacial polarization are strongly related to the surface status of the dispersed particles.

Material Design and Experimental Analysis of a New Type of Semiconductor ER Fluids

To improve the electrorheological effect of electrorheological fluid (ERF), a new type of the electrosensitive particle material, polynaphthalene quinone was prepared, whose molecules contain blended atoms of nitrogen, oxygen, sulphur and big π bond conjugate system. In both DC and AC electric fields, the ERF material showed a distinct ER effect. Especially, in the alternating electric field, the shear stress of this material versus AC voltage has a better quadratic relation than that of the other materials. The experimental data showed that organic semiconductor polymers with big π bond conjugate system are a new type of electrosensitive particle materials which are worth well developing.

Research on the Influence of Spring Stiffness on the Electrorheological Isolator

The problem of electrorheological(ER) technology’s application in the vibration isolation system is emphatically studied. Based on the particular characteristics of the electrorheological fluid (ERF) tunable damping, a metal-spring ER isolator is designed and its working principle is mainly discussed. By theoretical analysis of its simplified physical model, the dynamic response of an ER isolator is sensitive to the system equivalent spring stiffness K and ERF damping coefficient C. According to the dynamic performance tests, the result confirms that applying different electric field strength can change the dynamic peculiarity of the metal-spring ER isolator. The configuration design parameters of the ER equipment, such as the stiffness ratio of two fluid chambers and the size of the electric field, are important factors for the tunable range of ER isolator.

Theoretical Study and Structural Design of ERF Shock Absorbers

Electrorheologica (ER) technique is a developing technology. In a wide range of engineering applications of ER fluid, shock absorbers employing ER fluids, whose damping force can be controlled continuously and promptly through electric signals, is one of the most prospective applications of ER fluid. In this paper, the theoretical midel and method to predict the damping force of ERF shock absorbers are established.

Electrorheological effect of Ti-bearing blast furnace slag with different TiC contents at 1500°C

The electrorheological properties of CaO–SiO2–Al2O3–MgO–TiO2–Ti C slags were investigated to enhance understanding of the effect of TiC addition on the viscosity, yield stress, and fluid pattern of Ti-bearing slags in a direct-current electric field. The viscosities and shear stresses of 4wt% and 8wt% Ti C slags were found to increase substantially with increasing electric field intensity, whereas virtually no rheological changes were observed in the 0wt% TiC slag. The Herschel–Bulkley model was applied to demonstrate that the fluid pattern of the 4wt% TiC slag was converted from that of a Newtonian fluid to that of a Bingham fluid in response to the applied electric field; and the static yield stress increased linearly with the square of the electric field intensity.

Polar molecule dominated electrorheological effect

The yield stress of our newly developed electrorheological （ER） fluids consisting of dielectric nano-particles suspended in silicone oil reaches hundreds of kPa, which is orders of magnitude higher than that of conventional ones. We found that the polar molecules adsorbed on the particles play a decisive role in such new ER fluids. To explain this polar molecule dominated ER （PM-ER） effect a model is proposed based on the interaction of polar molecule-charge between the particles, where the local electric field is significantly enhanced and results in the polar molecules aligning in the direction of the electric field. The model can well explain the giant ER effect and a near-linear dependence of the yield stress on the electric field. The main effective factors for achieving high-performance PM-ER fluids are discussed. The PM-ER fluids with the yield stress higher than one MPa can be expected.

New Dispersed Phase of Electrorheological Fluids:TiO_2 Coating Graphite Particles

We have prepared novel coated particles, with a conductor graphite core and a dielectric TiO2 coating, as the dispersed phase of electrorheological fluids. One order of magnitude enhancement in the shear stress is obtained by using such composite particles, when it is compared with that of TiO2 particles. The experimental results show a way to get excellent ER system.

Preparation and Electrorheological Property of NaNO_3-Doped Y_2O_3 Material

A new class of electrorheological （ER） material using rare earth （RE = Y） oxide as the substrate, NaNO3- doped Y2O3 materials, were synthesized using Na2CO3 and Y（NO3）3 as starting materials. Their ER performance, dielectric property, and crystal structure were studied. The results show that doping NaNO3 can markedly enhance the ER activity of the Y2O3 material. For the suspensions of these materials in dimethyl silicone oil, a clear dependence of the shear stress on the doping degree of NANO3 was observed, and the optimal value of Na/Y molar ratio of 0.6 in doping degree was discovered, the relative viscosity ηr（ ηE/η0, E = 4.2 kV·mm^-1） of the suspensions is nine times higher than that of pure Y2O3 material. The new results of the relationship between ER effect and the microstructure were obtained, which are helpful for further understanding the mechanism of ER effect and synthesizing a good ER material.

Study on Viscoelastic Property of Nanometer SiO_2 Doped Rare Earth Carboxylate Grafting Poly-Silicone Liquid ERF

Nano-SiOdoped with rare earth carboxylate grafting continuous component of functional poly-silicone liquid, a kind of subsidence high-resistance. Electrorheological fluid (ERF) was synthesized. And its viscoelastic properties were investigated experimentally. The special polarization effect of rare earth in the ERF was also discussed. The forced oscillating behavior was obtained using a rheometer. The variation of the shear modulus of ERF subjected to various stress amplitude and frequency were investigated. The complex shear modulus and storage modulus of ERF were also given at different electric field intensities. Meanwhile, the creep and recovery characteristics of ERF were also measured. The equilibrium compliance Jc and the steady state recoverable compliance JR were investigated as a function of electric field strength and ratio of reactant, and the effect of ERF′s structure was analyzed. With increasing in electric field strength at fixed ratio of reactant, the plastic response diminishes, and the elastic behavior rose.

CAPTURE EFFECT OF ELECTRORHEOLOGICAL SUSPENSIONS IN FLOW FIELD

According to the results of experiments and theoretical analysis, a phenomenon called ＂capture effect＂ is put forward, which could be used to describe the particles dynamic behavior of electrorheological （ER） suspensions. Then a ＂structure-force＂ mathematical model is established to explain this effect based on electrostatic energy density equation. The analysis results show that the dynamic coupling process of ER suspensions under an external electric filed is the function not only of the electric intensity, but also of the dielectric properties and the structure form.

Field-Induced Structure and Pair Distribution Function of Fractals

The structure transitions in cluster-cluster aggregation (CCA) and diffusion-limited aggregation (DLA) under external electric fields have been investigated by computer simulations. With the increase of external electric field, there exists a structure transition from disorder to order, i. e., the aggregates change from fractals of diffusion-limited CCA and DLA to the electrorheological chains parallel to electric field. Pair distribution shows, the system changes from local order to long-range order gradually with the external field rising.

Preparation and Electrorheological Property of Y_4O(OH)_9(NO_3)-NH_4NO_3 Materials

The new electrorheologicai （ER） material, a particle material composed of Y4O（OH）9（NO3） and NH4NO3, was obtained. They display better ER performance. The shear stress of the suspension of Y4O （OH）9 （NO3） （ NH4NO3 ）2.8 material in dimethyl silicone oil reaches 1469 Pa at an electric field strength （E） of 4.2 kV·mm^-1 and the shear rate （7） of 150 s^-1 The relative shear stress, τ E/τ0（ τE and τ0 are the shear stresses at E = 4.2 and 0 kV·mm^-1 respectively）, is up to 29, which is 19 times that of pure Y2O3 material. The dielectric and conductive property of the materials play important roles in the modification of the ER effect of the particle materials. The researches on these new ER materials are very useful for obtaining a better understanding on the mechanism of the ER effect and finding an ideal ER material.

Effect of Carrier Liquid on Electrorheological Performance and Stability of Oxalate Group-modified TiO2 Suspensions

By using oxalate group-modified TiO2 nanoparticles as the dispersing phase, different kinds of silicone oil with various viscosities and terminal groups（hydroxyl, hydrogen, and methyl） were used as the dispersing media to prepare different electrorheological（ER） fluids. Their zero-field viscosity, yield stress under direct current electric fields, ER efficiency, shear stability, leakage current density, and sedimentation stability were tested to study the effect of carrier liquid on the properties of ER fluids. The results indicate that the zerofield viscosity, the yield stress, and the leakage current density increase with increasing viscosity of the silicone oils. The effects of the viscosity on the ER efficiency, the shear stability, and the sedimentation ratio depend on the competition between the viscous resistance and the aggregation of the particles. Among the three ER fluids prepared with silicone oil with different terminal groups, hydroxyl-terminated oil based sample has the highest zero-field viscosity, the highest field-induced yield stress and ER efficiency, the largest current density, and the best sedimentation stability.