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 ma...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.展开更多
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 conv...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.展开更多
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...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.展开更多
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 ...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.展开更多
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 obt...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.展开更多
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 performanc...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.展开更多
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） susp...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.展开更多
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） （ ...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.展开更多
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 me...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.展开更多
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 deduc...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.展开更多
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 ...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.展开更多
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 vi...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.展开更多
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...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.展开更多
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 ...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.展开更多
A new modified conductivity model was established to predict the shear yield stress of electrorheological fluids (ERF). By using a cell equivalent method, the present model can deal with the face-center square structu...A new modified conductivity model was established to predict the shear yield stress of electrorheological fluids (ERF). By using a cell equivalent method, the present model can deal with the face-center square structure of ERF. Combining the scheme of the classical conductivity model for the single-chain structure, a new formula for the prediction of the shear yield stress of ERF was set up. The influences of the separation distance of the particles, the volume fraction of the particles and the applied electric field on the shear yield stress were investigated.展开更多
A multifunctional material with both electrorheological（ER） performance and luminescence property was synthesized by a simple coprecipitation. The tetrabutyl titanate, as well as the Tb（NO3）3·6H2O and sulphos...A multifunctional material with both electrorheological（ER） performance and luminescence property was synthesized by a simple coprecipitation. The tetrabutyl titanate, as well as the Tb（NO3）3·6H2O and sulphosalicylic acid（C7H6O6S·2H2O, SSA） were chosen as starting materials. The composition, ER performance and luminescence property of the material were studied. The results showed that a novel material（TiTbSSA） with both ER performance and luminescence property was obtained. The relative shear stress τr（τr=τE/τ0, τE and τ0 were the shear stresses of the suspension with and without an applied electric field） of the suspension（30 wt.%） of the material in silicone oil reached 32.7 at a shear rate of 12.5 s–1 and an electric field strength of 4 kV/mm（DC electric field）. The material containing the rare earth（RE=Tb） complex exhibited fine luminescence performance and higher ER activity. Therefore, it is a novel multifunction material which would have wide application prospect.展开更多
The electrorheological (ER) fluids are colloidal suspension of highly polarizable particles in a non-conducting solvent. Chains of submicron-sized particles formed along an applied DC electric field by the so-called e...The electrorheological (ER) fluids are colloidal suspension of highly polarizable particles in a non-conducting solvent. Chains of submicron-sized particles formed along an applied DC electric field by the so-called electrorheological effect. According to the obvious change of transmittance of the ER fluids in a DC electric field when the polarized particles arranged along the field, the model of smart window was proposed by sandwiching the ER fluids based on titania particles coated with silica between a pair of In-Sn oxide (ITO) coated glasses. The solar transmittance change as much as 48.0% was obtained with the wavelength of 500 nm at the maximum on applying and removing the electric field of 500 V/mm.展开更多
Using palygorskite(PAL)as template,the PAL/TiO_(2)/PANI nano-rods were synthesized by heterogeneous precipitation and in-situ polymerization.The synthesized PAL/TiO_(2)/PANI nanorods were used as a novel electrorheolo...Using palygorskite(PAL)as template,the PAL/TiO_(2)/PANI nano-rods were synthesized by heterogeneous precipitation and in-situ polymerization.The synthesized PAL/TiO_(2)/PANI nanorods were used as a novel electrorheological(ER)fluid by mixing with silicone oil,which showed excellent ER effect.The yield stress of the PAL/TiO_(2)/PANI based ER fluid(15 vol%)reached 8.8 kPa under 4 kV mm^(−1) electric field.The dynamic shear stress of the PAL/TiO_(2)/PANI based ER fluid could maintain a stable level in the shear rate range of 0.1–100 s^(−1).Furthermore,the PAL/TiO_(2)/PANI ER fluid exhibited excellent suspension stability.展开更多
It is well known that constant or time-varying electric fields can induce phase changes in electrorheological(ER) fluids, from a liquid to semi-solid state, provided the field strength is larger than some critical val...It is well known that constant or time-varying electric fields can induce phase changes in electrorheological(ER) fluids, from a liquid to semi-solid state, provided the field strength is larger than some critical value. We describe here an experimental and theoretical study considering yet a different class of phase changes, specifically those for an ER fluid in the presence of both shear flow and a time-varying electric field. We note that as the frequency of the field is decreased, the ER fluid will go from a liquid to an intermediate transition state, and eventually to a shear banding state. Our theoretical analysis further indicates that this phase change originates from competing effects of viscous and electrical forces. Ultimately, we conclude that it is possible to achieve various states and corresponding(desired)macroscopic properties of dynamic colloidal suspensions by adjusting the frequency of the externally applied electric field.展开更多
文摘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.
文摘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.
基金financial support from the National Natural Science Foundation of China(No.52174066,No.51534007).
文摘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.
基金Project supported by the National Key Research and Development Program of China(Grant No.2017YFA0403000)the National Natural Science Foundation of China(Grant No.11874430).
文摘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.
基金the National Natural Science Foundation of China! (No.19834020).
文摘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.
文摘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.
文摘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.
文摘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.
基金Funded by the National Natural Science Foundation of China(51478088)
文摘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.
文摘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.
基金Project (50771089) supported by the National Natural Science Foundation of China
文摘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.
基金Turkish Scientific and Technological Research Council for the financial support of this work (Project No: 112T811)
文摘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.
基金The authors are thankful to the support of the National Natural Science Foundation of China(Grant No.50135030).
文摘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.
文摘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.
文摘A new modified conductivity model was established to predict the shear yield stress of electrorheological fluids (ERF). By using a cell equivalent method, the present model can deal with the face-center square structure of ERF. Combining the scheme of the classical conductivity model for the single-chain structure, a new formula for the prediction of the shear yield stress of ERF was set up. The influences of the separation distance of the particles, the volume fraction of the particles and the applied electric field on the shear yield stress were investigated.
基金Project supported by National Natural Science Foundation of China(10704041,90922033,21071008)the National Basic Research Program of China(2013CB933401,2010CB934601)
文摘A multifunctional material with both electrorheological（ER） performance and luminescence property was synthesized by a simple coprecipitation. The tetrabutyl titanate, as well as the Tb（NO3）3·6H2O and sulphosalicylic acid（C7H6O6S·2H2O, SSA） were chosen as starting materials. The composition, ER performance and luminescence property of the material were studied. The results showed that a novel material（TiTbSSA） with both ER performance and luminescence property was obtained. The relative shear stress τr（τr=τE/τ0, τE and τ0 were the shear stresses of the suspension with and without an applied electric field） of the suspension（30 wt.%） of the material in silicone oil reached 32.7 at a shear rate of 12.5 s–1 and an electric field strength of 4 kV/mm（DC electric field）. The material containing the rare earth（RE=Tb） complex exhibited fine luminescence performance and higher ER activity. Therefore, it is a novel multifunction material which would have wide application prospect.
基金The authors greatly appreciated financial support from the National Natural Science Foundation of China mostly under projecl No.59672011 the Foundation for the Youth Faculty at UEST of China partially.
文摘The electrorheological (ER) fluids are colloidal suspension of highly polarizable particles in a non-conducting solvent. Chains of submicron-sized particles formed along an applied DC electric field by the so-called electrorheological effect. According to the obvious change of transmittance of the ER fluids in a DC electric field when the polarized particles arranged along the field, the model of smart window was proposed by sandwiching the ER fluids based on titania particles coated with silica between a pair of In-Sn oxide (ITO) coated glasses. The solar transmittance change as much as 48.0% was obtained with the wavelength of 500 nm at the maximum on applying and removing the electric field of 500 V/mm.
基金support by the Jiangsu Key R&D program(BE2019072)the Ningbo Natural Science Foundation(2018A610167,2018A610322).
文摘Using palygorskite(PAL)as template,the PAL/TiO_(2)/PANI nano-rods were synthesized by heterogeneous precipitation and in-situ polymerization.The synthesized PAL/TiO_(2)/PANI nanorods were used as a novel electrorheological(ER)fluid by mixing with silicone oil,which showed excellent ER effect.The yield stress of the PAL/TiO_(2)/PANI based ER fluid(15 vol%)reached 8.8 kPa under 4 kV mm^(−1) electric field.The dynamic shear stress of the PAL/TiO_(2)/PANI based ER fluid could maintain a stable level in the shear rate range of 0.1–100 s^(−1).Furthermore,the PAL/TiO_(2)/PANI ER fluid exhibited excellent suspension stability.
基金Supported by the National Natural Science Foundation of China under Grant Nos.10334020,10974030,10574027,11222544the Fok Ying Tung Education Foundation under Grant No.131008+1 种基金the Program for New Century Excellent Talents in University(NCET-120121)the CNKBRSF under Grant No.2011CB922004
文摘It is well known that constant or time-varying electric fields can induce phase changes in electrorheological(ER) fluids, from a liquid to semi-solid state, provided the field strength is larger than some critical value. We describe here an experimental and theoretical study considering yet a different class of phase changes, specifically those for an ER fluid in the presence of both shear flow and a time-varying electric field. We note that as the frequency of the field is decreased, the ER fluid will go from a liquid to an intermediate transition state, and eventually to a shear banding state. Our theoretical analysis further indicates that this phase change originates from competing effects of viscous and electrical forces. Ultimately, we conclude that it is possible to achieve various states and corresponding(desired)macroscopic properties of dynamic colloidal suspensions by adjusting the frequency of the externally applied electric field.
