Excellent Electrorheological Research Articles

Preparation and electrorheological properties of a squared chromium-ion-doped MOF-Ti/SiO2 composite

Herein, a core–shell structured nanocomposite with excellent electrorheological (ER) properties was successfully prepared for studying ER fluids (ERFs). First, the material was prepared by using chromium (Cr)-ion-doped Ti-based metal–organic frameworks (MOF-Ti) as a template using the solvothermal method, followed by coating with SiO2 via hydrolysis to form Cr-MOF-Ti/SiO2 composite. In combination with the advantages of the MOF-Ti structure, such as more active sites and a high specific surface area, doping with transition metal ions and coating with SiO2 can effectively enhance the interfacial polarisation of the obtained Cr-MOF-Ti/SiO2 composite and thus improve its ER performance. Analyses were conducted on the morphology, elemental composition and functional groups of the materials using scanning electron microscopy, transmission electron microscopy, X-ray diffractometer, X-ray photoelectron spectroscopy, Fourier transform infrared spectroscopy, Brunauer–Emmett–Teller and dielectric analysis. The results indicate successful Cr-ion doping and SiO2 coating. The ER performance of the composite particles was also evaluated. The results indicate that the SiO2-coated sample exhibits superior ER properties, including a smaller leakage current density and higher shear stress. Moreover, the SiO2 coating enhanced the interfacial polarisation capability of Cr-MOF-Ti, as verified by the dielectric data.

Dynamic Response of Polyindole Coated Zinc Ferrite Particle Suspension under an Electric Field.

ZnFe2O4 particles initially synthesized through a simple solvothermal method were coated using polyindole (PIn) to prepare an actively controllable core-shell typed hybrid material under both electric and magnetic fields. An advantage of this process is not needing to add the stabilizers or surfactants commonly used for uniform coating when synthesizing core or shell-structured particles. The synthesized ZnFe2O4/PIn particles have a lower density than conventional magnetic particles and have suitable properties as electrorheological (ER) particles. The expected spherical shape of the particles was proven using both scanning electron microscopy and transmission electron microscopy. The chemical characterization was performed using Fourier-transform infrared spectroscopy and X-ray diffraction analysis. To analyze the rheological properties, a ZnFe2O4/PIn based suspension was prepared, and dynamic rheological measurements were performed for different electric field strengths using a rotary rheometer. Both dynamic and elastic yield stresses of the ER fluid had a slope of 1.5, corresponding to the conductivity model. Excellent ER effect was confirmed through rheological analysis, and the prepared ER fluid had a reversible and immediate response to repeated electric fields.

Temperature-dependent electrorheology of a suspension based on copolymeric P(NIPAM-co-[AMIm]Cl) colloidal particles

A imidazolium-based poly (ionic liquid), poly(1-allyl-3-methyl imidazolium chloride) (P[AMIm]Cl) was combined with the temperature-sensitive polymer poly(N-isopropylacrylamide) (PNIPAM) via random copolymerisation of the monomers [AMIm]Cl and NIPAM. The synthesised copolymer was characterised by nuclear magnetic resonance (NMR), Fourier transform infrared (FTIR) spectroscopy, and scanning electron microscope (SEM). Then its stimuli-responsive properties were studied at different electric field strengths and temperatures when it was dispersed in silicone oil. It was found that the colloidal copolymer particles were electro-responsive, showing excellent electrorheological (ER) effect. It was interesting that the ER effect of the copolymer was temperature-dependent. As the temperature increased from 5 °C to 50 °C, the dynamic yield stress of the suspension was found to increase with temperature. The temperature dependence of both yield stress and current density became stronger as the temperature was higher than 30 °C. The significant temperature-dependence of the suspension was attributed to the PNIPAM segment in the copolymer which could be swelled by silicone oil at higher temperature.

A stable high-performance isotropic electrorheological elastomer towards controllable and reversible circular motion

In this paper, two kinds of isotropic giant electrorheological elastomers (GERE) were prepared with urea-coated barium titanyl oxalate nanoparticles as dielectric particles filler, poly (dimethyl siloxane) (PDMS) as an elastic matrix and silicone oil as a plasticizer. Such GEREs are far superior to other isotropic and even anisotropic electrorheological elastomers (EREs), showing excellent electrorheological (ER) performance. The theoretic mechanism in elastomers prepared by us should be explained by saturation surface polarization or orientational polarization model. More interestingly, the storage modulus increment (ΔG′) of GEREs displays curvilinear dependence on the electric field due to poor particle mobility and different mobility under different electric fields, rather than a predicted linear variation. After testing their viscoelastic and dielectric properties and microstructures, we found that too high of the powder content leads to the serious agglomeration of particles and the performance degradation of the elastomer. An incorporation of silicone oil improved the dispersion state and wettability between the particles and matrix. At the same time, silicone oil reduced the hardness of the matrix and made the particles align more easily in the PDMS matrix. Lower initial modulus and higher field-induced modulus make GEREs containing silicone oil have ultrahigh storage modulus sensitivity, in which the best-performing sample achieved a storage modulus change exceeding 400 kPa and attained a maximum relative ER effect of 3280% at 3 kV/mm. Finally, the GERE was used to reversibly control the amplitude of circular motion within seconds by varying electric fields, revealing broad potential application in vibration control.

Nanocrystalline ceria: a novel material for electrorheological fluids

Nanocrystalline CeO2shows intriguing electroheological performance.

Fabrication and electric-field response of spherical BaTiO3 particles with high tetragonality

Electrorheological elastomer (ERE) is a member of smart material family. Many efforts have been made to develop high-performance EREs for preparing active electrorheological (ER) particles. In this work, an excellent ER particles named spherical tetragonal BaTiO3 were successfully synthesized by hydrothermal method at different conditions using Ba(OH)2·8H2O and amorphous TiO2 as original materials. Analysis of the structure and morphology of the synthesized particles with Raman, XRD, SEM techniques indicates that the additives play a crucial role in determining the surface morphology of the particles. Additionally, we discovered that the spherical tetragonal BaTiO3 particles with different surface morphology possess different tetragonality, surface hydrophilicity and dielectric property, and thus exhibit distinct electric-field response. The response of the BaTiO3 particles to electric-field is in the order of daisy-shaped > walnut-shaped > sphere particles. Further experiments reveal that high tetragonality, fine dielectric performance and super surface hydrophilicity of BaTiO3 particles are the major power in boosting their electric-field response.

LANTHANUM TITANATE NANOPARTICLES ER FLUIDS WITH HIGH PERFORMANCE

A new type of electrorheological (ER) fluid consisting of lanthanum titanate (LTO) nanoparticles is developed. The ER fluids were prepared by suspending LTO powder in silicone oil and the particles were fabricated by wet chemical method. This ER fluid shows excellent ER properties: The static yield stress reaches over 150 kPa under 5 kV/mm with linear dependence on the applied DC electric field, and the current density is below 10 μA/cm2. In order to investigate the affect factor on the ER behavior, the LTO powder were heated under different temperatures. The ER performances of two particles treated under different temperatures were compared and the composition changes for those particles were analyzed with TG-FTIR technique. It was found that the static yield stress of the suspensions fell from over 150 kPa to about 40 kPa and the current densities decreased prominently as the rise of the heating temperature. TG-FTIR analysis indicated that polar groups remained in the particles such as alkyl group, hydroxyl group and carbonyl group etc., contribute to the ER effect significantly. The experimental results are helpful to understand the mechanism of the high ER effect and to synthesize better ER materials.

Preparation of Stannum and Titanium Precipitation Particles and its High Electrorheological Properties

A type of stannum and titanium precipitation (STP) particle was synthesized by means of co-precipitation method. Suspensions made by dispersing the STP particles in silicone oil exhibit excellent electrorheological (ER) effect with high yield stress, high shear stress at higher shear rate. The static yield stress of the STP ER can be up to 84 kPa at an electric field of 5 kV/mm. The high yield stress and its near-linear dependence on the electric field indicate that the rheological behaviors of our STP ER fluid can be explained by the model of the polar molecule dominated ER (PMER) effect, which arises from the alignment of polar molecules in the gap between neighboring particles.

Titanium oxide nanoparticle modified with chromium ion and its giant electrorheological activity

Titanium oxide nanoparticles modified with chromium ion are fabricated via a modified hydrolysis methods. The X-ray diffraction analyses, Fourier transform-infrared spectrometry, transmitting electron microscopy, etc., are used to determine the structure of the nanoparticles. The results show that modified titanium oxide nanoparticles possess small size distribution. The average particle size is 120 nm. The electrorheological (ER) activity was studied by the rheological curve and yield stress under an electric field. An excellent ER effect is found with the suspension of modified titanium oxide nanoparticles dispersed in silicone oil. At the DC electric field, modified titanium oxide nanoparticles ER fluid not only possess high static yield stress, but also have good dynamic shear stress. The large Δ ε′ and proper polarization response in this nanoparticles ER fluid induces a strong and stable interaction among the particles. These may be the intrinsic reason for the huge enhancement of ER effect. Furthermore good sedimentation property of its electrorheological suspension is observed.

Electrorheology of Suspensions of Copper Phthalocyanine-Doped Mesoporous Silica

Mesoporous silica(MPS) particles are synthesized in the presence of templates of surfactant micelles and the doping treatments are carried out to form copper phthalocyanine(CuPh)-doped MPS. The rheological properties of suspensions of CuPh-doped MPS particles dispersed in a silicone oil are studied on the application of DC electric fields. The electrorheological(ER) effect of CuPh suspensions is very weak, although the CuPh compounds are well known as semiconducting materials and widely used in industries. However, the doping of CuPh into MPS causes a drastic increase in ER effect and conductivity of suspensions. It is generally accepted that the interparticle forces generated in electric fields are polarization forces due to the dielectric mismatch between the particles and continuous liquid phases. In some cases, the surface conduction of thin layers on the particles can play an important role in promoting the ER effect. The increase in surface conduction by doped CuPh on the MPS may be responsible for enhancement of ER effect. The doping of semiconducting materials into mesoporous particles provides a new formulation method of excellent ER particles.

Synthesis and electrorheological characterization of polymer containing amino and carboxy groups

A new polymer (poly[ N, N′-(2-amino-5-carboxy-1,3-phenylenedimethylene)-2,2′-diamino-4,4′-bithiazole], PACPDMDABT) containing amino and carboxy groups was synthesized. This polymer can be used as a disperse phase to prepare excellent electrorheological (ER) fluids. Several ER fluids were prepared (1) with the polymer in different type of disperse mediums (bromodiphenylmethane and silicone oil) and (2) with different polymer concentration in each type of the disperse medium. Rheological properties of the fluids were measured. Impact of the strength of the applied electric field, disperse phase concentration and different disperse mediums to the ER properties of the materials were measured and discussed. The results showed that ER properties of the fluids were improved as increase in the disperse phase concentration and as increase in the electric field strength. We also found that ER properties of the fluids depended on the densities of both polymer and disperse medium. Based on the results measured from two disperse mediums, the disperse medium with a closer match in density to the polymer showed better ER properties. Several key physical properties of the polymer were also measured by FTIR, thermogravimetric analysis and scanning electron microscopy.

Preparation and electrorheological properties of polyquin(2,3-b)acridine-12,14(5,7)dione-based suspensions

Novel polymeric electrorheological (ER) fluids were achieved by dispersing polyquin(2,3-b)acridine-12,14(5,7)dione (polyquinacridinedione, PQA) in bromodiphenylmethane (BDPM) and silicon oil, respectively; the conjugated polymer, PQA was synthesized via sequentially condensation, cyclization and oxidation from m-phenylenediamine and dimethyl 2,5-dioxocyclohexane-1,4-dicarboxylate. The structure characteristics of the PQA molecule and ER activity of the PQA-based suspensions were investigated. The results indicate that the PQA suspensions exhibited excellent ER activity both in BDPM and in silicon oil; the yield stress of the 30 wt.% PQA suspension in BDPM reaches up to 4 kPa under 3 kV/mm. The yield stress of the suspensions increases with the dielectric constant of the liquid media. The excellent ER activity of the suspensions is attributed to the unique molecular structure of PQA: the non-localized π bond and polarizable groups within PQA molecule, as well as the plane ladder-like structure of PQA molecule, leading to high polarization of the particles of PQA, and forming strong fibrillated chain- or even net-like assembly under electric field, which leads to remarkable yield stress. The results also show that, for the PQA suspension in DBPM, the yield stress is proportion to the squared electric field and weight percent of particles, the apparent viscosity linearly increases with the squared electric field.

Synthesis and characterization of polysaccharide phosphates based electrorheological fluids

Polysaccharide phosphate particles were synthesized via an esterification process with various molar concentrations of phosphoric acid using both cellulose and potato starch. The particles were characterized with thermogravimetric analysis, scanning electron microscopy, and an inductively coupled plasma-mass spectrometer. These particles were then dispersed in a silicone oil to make anhydrous electrorheological (ER) fluids. Each sample of polysaccharide particles used in this study exhibits thermal stability and possesses excellent ER properties when measured as functions of both particle concentration and electric field strength by a rheometer equipped with a high voltage generator. A difference in the flow behavior for both potato starch and cellulose- phosphates-based ER fluids was also identified.

Electrorheological properties of suspensions of semiconducting particles

Semiconducting tin dioxide particles were covered with insulating layer and its effect on electrorheological (ER) properties of the suspensions was examined under oscillatory and steady shear. When the particles were coated with titanium dioxide by hydrolyzing titanium tetraisopropoxide and heat‐treated at 600 °C, the suspension in a silicone oil showed a high yield stress at an electric field of 2.0 kV mm−1. However, since the titanium dioxide layer was semiconducting, the current density was about 0.2 mA cm−2 and would not be applicable to practical device. Using aluminium ion, the titanium dioxide can be doped from a semiconducting to an insulating state. The particles covered with surface layer consisting of titanium dioxide and aluminum oxide provided excellent ER fluids in water‐free systems. The coating of semiconducting particles by hydrolysis of alkoxides is very useful for surface modification of particles to improve the ER performance of suspensions.

Effect of adsorbed water on the electrorheology of silica suspensions

Monodisperse silica particles were formed by hydrolyzing tetraethylorthosilicate in an ethanol solution and the silica suspensions dispersed in a silicone oil were prepared by a different procedure. The effects of adsorbed water on the electrorheological (ER) behavior were studied under oscillatory shear. The amounts of adsorbed water and surface silanol groups were determined by thermogravimetric analysis. The magnitude of the complex viscosity, |η ∗|, increases with the application of electric fields. The physically adsorbed water is primarily responsible for the ER effect. However, the fluids containing large amounts of adsorbed water do not always show excellent ER performance. The surface silanol groups have an important role in promoting the ER effect. Not only the amount but also the situation of silanol groups determines the ER activity of adsorbed water.

Electrorheological Properties of Suspensions of Semiconducting Particles

Semiconducting tin dioxide particles were covered with insulating layer and its effect on electrorheological (ER) properties of the suspensions was examined under oscillatory and steady shear. When the particles were coated with titanium dioxide by hydrolyzing titanium tetraisopropoxide and heat‐treated at 600 °C, the suspension in a silicone oil showed a high yield stress at an electric field of 2.0 kV mm−1. However, since the titanium dioxide layer was semiconducting, the current density was about 0.2 mA cm−2 and would not be applicable to practical device. Using aluminium ion, the titanium dioxide can be doped from a semiconducting to an insulating state. The particles covered with surface layer consisting of titanium dioxide and aluminum oxide provided excellent ER fluids in water‐free systems. The coating of semiconducting particles by hydrolysis of alkoxides is very useful for surface modification of particles to improve the ER performance of suspensions.