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.

Preparation of Y_2O_3 Nanoparticles Organosol by Microemulsion Method

Y 2O 3 nanoparticles organosol coated with DBS was prepared by microemulsion method. The optimum preparative conditions of Y 2O 3 nanoparticles organosol were obtained. TEM analysis indicates that the prepared Y 2O 3 nanoparticles are spherical in shape. The size is about 5 nm. The size distribution is in the narrow range and no agglomerates are observed. Y 2O 3 nanoparticles coated with DBS are easy to dissolve in weak polar solvents.

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.

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.

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.

An Efficient Route to Prepare Metal Organosols by Phase Transfer Procedure

Silver and gold organosols are easily prepared by transferring nanoparticles from aqueous phase into isooctane with high efficiency (>90%). Concentrations of sodium oleate and magnesium chloride have crucial effects on the transfer efficiency. Based on the UV-visible absorption spectra, TEM micrographs of nanoparticles, as well as molecular modeling calculation about the adsorption conformation of sodium oleate molecules, a possible phase transfer mechanism is proposed.

Smart Property of Homogeneous Electrorheological Fluid and Its Application in Reducing Seismic Responses of Engineering Structures

The smart properties of homogeneous electrorheological fluid (HERF) containing side-chain type liquid crystalline polymer were studied and an actual HERF damper with an adjustable viscosity was produced.A mechanical model of the HERF smart damper was established on the basis of experiment and theoretical analysis.Then a controlled equation of SDOF structure by HERF damper was derived and a semi active control strategy based on optimal sliding displacement of damper was presented.The simulation results for a single story frame structure indicate that HERF,which may avoid some defects of common particles suspended ER fluids,is an excellent smart material with better stability.Using the semi active control strategy presented,HERF smart damper controlled could effectively reduce seismic responses of structures and keeps the control stable at all times.

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.

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.

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.

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.

Effect of surfactant on the dielectric and electrorheological properties of zinc borate/silicone oil dispersions

Zinc borate(ZB)particles dispersed in silicone oil(SO)at concentrations of φ=5vol%-20vol% were subjected to dielectric analysis to elucidate their polarization strength,time,and mechanism.Results revealed that all virgin dispersions lacked polarization.Triton X-100,a non-ionic surfactant,was added to ZB/SO dispersions to enhance the polarizability of ZB particles.The addition of 1vol% Triton X-100 enhanced the polarizability of ZB/SO dispersions,and the 15vol% ZB/SO system provided the highest dielectric difference Δε′(the difference in ε′values at zero and infinite frequency,Δε′=ε0–ε∝)of 3.64.The electrorheological(ER)activities of the ZB/SO/Triton-X dispersion system were determined through the ER response test,and viscoelastic behaviors were investigated via oscillation tests.A recoverable deformation of 36% under an applied electrical field strength of 1.5 kV/mm was detected through creep and creep recovery tests.

Dynamics simulation of electrorheological suspensions in poiseuille flow field

Based on a modified Maxwell-Wagner model,molecular dynamics is carried out to simulate the structural changes of ER(electrorheological) suspensions in a poiseuille flow field.The simulation results show that the flow assists in the collection of particles at the electrodes under a low pressure gradient,and the negative ER effect will show under a high pressure gradient.By analyzing the relationship curves of the shear stress and the pressure gradient in different relaxation time,it is found that for the same kind of ER suspensions materials,there is an optimal dielectric relaxation frequency.

Sol-Gel Preparation of Graphite/TiO_2 Composite Particles and Their Electrorheological Effect

Graphite/TiO2 composite particles were obtained by sol-gel technique in this paper. The structure and characteristic of the composite particles are analyzed by XRD, SEM and TG-DTA. The electrorheological properties of the ER fluid containing the particles were measured by a Couette-type rheometer under shear rates of 1-136 s-1 and AC electric fields of 0-3 kV/mm. The experimental results show that the leaking current density of the ER fluid is higher than that of pure titanium dioxide particles dispersed in damping oil. The shear yield stress of the ER fluid increases with increasing electric field and exhibits a typical Bingham flow behavior. The suspension demonstrates an excellent ER performance (τ/τo=1200) compared with conventional ER fluids (τ/τ0 ≤500). The sedimentation of the ER fluid is improved obviously due to the coating effect of the particles.

PERCOLATION TRANSITION IN ELECTRORHEOLOGICAL FLUIDS

The electric conductivity, dynamic modulus and yield stress of the developed electrorheolo-gical fluid (ERF) are measured at different volume fraction and different electric field strengthusing a modified Rheometrics Mechanical Spectrometer (Model 605). The percolation theory isintroduced to explain electrorheological effect and found that the ERF′s have the similarpercolated network structure as that of other ordinary suspensions with a critical volume fractionvalue independent of electric field strength. A master curve of dimensionless modulus againstdimensionless volume fraction is obtained. which shows that the essence of ER phenomenonactually is one kind of the second ofder phase transition.

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.

The Synthesis and Electrorheological Properties of BaTiO_3-coated PMMA Microspheres

Coated-PMMA microspheres consisting of poly （methyl methacrylate）（PMMA） core and barium titanate （BaTiO3） shell were synthesized by the modified sol-gel processing and then adopted as an electrorheological （ER） materials. The structure and morphology of coated powders were chyfecterized by SEM and FT-IR; the shear stress of the suspensions of coated-PMMA particles and pure PMMA particles in silicone oil with a 20 vol% were investigated. The results show that the BaTiO3 coated PMMA microspheres based suspension in silicone oil exhibited typical ER behavior and stronger ER effects.