Electrorheology of aniline oligomers

Aniline oligomers were prepared by the oxidation of aniline with p-benzoquinone in aqueous solutions of methanesulfonic acid (MSA) of various concentrations. Their molecular structures were assessed by Fourier transform infrared spectroscopy. The electrorheological (ER) behavior of their silicone oil suspensions under applied electric field has been investigated. Shear stress at a low shear rate, τ _0.9, was used as a criterion of the rigidity of internal structures created by the application of an electric field. It was established from the fitting of the dielectric spectra of the suspensions with the Havriliak–Negami model that dielectric relaxation strength, as a degree of polarization induced by an external field contributing to the enhanced ER effect, increases and relaxation time, i.e., the response of the particle to the application of the field, decreases when a higher molar concentration of MSA is used. The best values were observed for suspensions of the sample prepared in the presence of 0.5 M of MSA. This suspension creates stiff internal structures under an applied electric field strength of 2 kV mm^?1 with τ _0.9 of nearly 50 Pa, which is even slightly of higher value than that obtained for standard polyaniline base ER suspension measured at the same conditions. The concentration of the MSA used in the preparation of oligomers seems to be a crucial factor influencing the conductivity, dielectric properties and, consequently, rheological behavior, and finally ER activity of their suspensions.     

Development and flow evaluation of electro-rheological nano-suspensions

An attempt has been made to develop a candidate for electro-rheological (ER) nano-suspensions based on anatase titanium dioxide with a particle diameter around 300 nm. The micro-gap flow behavior and microstructure were evaluated for a suspension with a particle volume fraction of 8.8 vol.%. The ER effect was investigated for the nano-suspension. The effect of shearing time on the ER responses was also investigated. The ER effect was discussed in comparison to the effect previously reported for the nano-suspension based on rutile titanium dioxide with a particle diameter around 15 nm.     

Fabrication and stimuli response of rice husk-based microcrystalline cellulose particle suspension under electric fields

We report on the electro-responsive electrorheological (ER) properties of microcrystalline cellulose (MCC) particles. It was synthesized from raw rice husk (Downes Rice) through the 3-step preparation of alkali treatment, bleaching, and hydrolysis. The MCC particles with mean particle size about 26 μm were characterized by scanning electron microscopy, Fourier transform infrared spectroscopy and thermal gravimetric analysis. The MCC particles were then dispersed in silicone oil to create an ER fluid; its dramatic electro-responsive phase changes under an applied electric field were observed by an optical microscopy. The effect of electric field strengths on ER performances of the ER fluid were determined using a rotational rheometer equipped with a high-voltage generator from the controlled shear rate mode and dynamic oscillation measurements. The fluid showed typical ER effects of Bingham fluid behavior with yield stress and viscoelastic properties under an applied electric field.     

Effects of medium oil on electroresponsive characteristics of chitosan suspensions

Biocompatible chitosan particle suspensions in host oils of corn, soybean, and silicone were prepared and their electrorheological (ER) characteristics were examined under the imposition of electric fields. The effects of the weight concentration of particulate chitosan and the strength of the applied electric field on ER response in the various chitosan particle suspensions were investigated via measurements of rheological properties including flow curve, shear viscosity, and yield stress. The yield stresses of the three different chitosan–oil systems showed different values of slope in the electric field, but all data were found to fit well with our previously proposed universal scaling function.     

Electrorheological properties of perchloric acid-doped polythiophene suspensions

Poly(3-thiopheneacetic acid), PTAA, was synthesized via an oxidative polymerization and doped with perchloric acid to control its conductivity. The rheological properties of the HClO₄-doped PTAA/silicone oil suspensions were measured in oscillatory shear to investigate the effects of electric field strength, particle concentration, and particle conductivity on electrorheological (ER) characteristics. The PTAA-based ER fluids exhibit viscoelastic behavior under an applied electric field and the ER response is amplified with increase of electric field strength. The dynamic moduli, G and G, increase dramatically by ten orders of magnitude when the field strength is increased to 2 kV/mm. The suspensions exhibit a transition from fluid-like to solid-like behavior as the field strength increases, and reach a saturated ER response at a field strength of 1 kV/mm. Increase of particle concentration and particle conductivity result in a lower transition field strength. Scaling arguments are presented which successfully superpose the scaled moduli at various electric field strengths onto a single master function of the dimensionless frequency.     

Electrorheological properties of polyaniline suspensions: field-induced liquid to solid transition and residual gel structure

Polyaniline (PANI) was synthesized via oxidative coupling polymerization in acid conditions and de-doped in solution of ammonia. The electrorheological (ER) properties of the PANI/silicone oil suspensions were investigated in oscillatory shear as functions of electric field strength, particle concentration, and host fluid viscosity. Consistent with literature, the PANI ER fluid exhibits viscoelastic behavior under the applied electric field and the ER response is strongly enhanced with increasing electric field strength and particle concentration. The dynamic moduli, G' and G' increase dramatically, by 5 orders of magnitude, as the electric field strength is increased to 2 kV/mm. A viscoelastic liquid to solid transition occurs at a critical electric field strength, in the range Ec = 50-200 V/mm, whose value depends on particle concentration and host fluid viscosity. The fibrillar structure formed in the presence of the applied field has a static yield strength tau(y), whose value scales with electric field strength as tau(y) approximately E(1.88). When the field is switched off a residual structure remains, whose yield stress increases with the strength of the applied field and particle concentration. When the applied stress exceeds the yield stress of the residual structure, fast, fully reversible switching of the ER response is obtained.     

Electrorheology and creep-recovery behavior of conducting polythiophene/poly(oxymethylene)-blend suspensions

Electrorheological properties and creep-recovery behavior of polythiophene/polyoxymethylene-blend having PT（50%）/POM（50%） composition were investigated.Particle size,conductivity and dielectric values were measured to be 24.77μm,3.85×10^-5 S·m^-1 and 26.75,respectively.Sedimentation ratio was measured to be 64%at the end of 16 days.The effects of dispersed particle volume fraction,external electric field strength,shear rate,frequency and temperature on ER properties and storage modulus of PT/POM-blend/silicone oil（SO） suspensions were examined.Enhancement were observed in the electric field viscosities of the suspensions and thus they were classified as a smart material.Shear thinning non-Newtonian viscoelastic behavior was determined for PT/POM-blend/SO system.Further,time-dependent deformation was examined by creep-recovery tests and recoverable viscoelastic deformation established.     

Preparation and electrorheological property of rare earth modified amorphous BaxSr1-xTiO3 gel electrorheological fluid

In this paper, we present a newly developed rare earth modified amorphous barium strontium titanate (Ba(x)Sr(1-x)TiO3) gel/silicone oil electrorheological (ER) fluid. The ER behaviors of suspensions of pure and rare earth modified amorphous Ba(x)Sr(1-x)TiO3 particles in silicone oil have been investigated under a dc electric field. The shear yield stress of the rare earth modified amorphous BaTiO3 gel/silicone oil ER fluid could reach 14.9 kPa at E=3.5 kV/mm while the leaking current density was very low, about 7.64 microA/cm2. The ER fluids with a higher volume fraction had a higher current density and a higher shear yield stress under the same electric field. The ER fluid has a long-term stability against sedimentation. The problem of caking was not serious and the agglomerated particles could be easily broken up by strongly stirring.     

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.     

二氧化硅负载胺丙基硅烷电流变流体

研究用二氧化硅负载胺丙基三乙氧基硅烷［ＮＨ２（ＣＨ２）３Ｓｉ（ＯＥｔ）３］作为分散颗粒，制备无水型的电流变（ＥＲ）流体．考察电场强度（Ｅ）、剪切速率（γ·）、分散颗粒含量、分散介质种类以及极性小分子等因素对ＥＲ流体流变性能的影响．结果发现，以硅油为分散介质，含分散颗粒为１５％（ｇ／ｍｌ）的流体，不添加任何活化剂，在γ·为８０６６ｓ－１时，Ｅ从０升至１６６６ｋＶ／ｍｍ，流体的表现粘度（ηａ）从０３９６Ｐａ．ｓ增大到１６６６８Ｐａ．ｓ．γ·提高，ηａ降低．分散颗粒含量增加，ηａ增大．用硅油作分散介质，ＥＲ效应比用矿物油或石蜡油显著．加入极性小分子苯胺，可以增强流体的ＥＲ效应，但随着苯胺含量增多，漏电流密度也增大．     

Synthesis and electrorheological characterization of emulsion-polymerized dodecylbenzenesulfonic acid doped polyaniline-based suspensions

The electrorheological (ER) properties of dodecylbenzenesulfonic acid (DBSA) doped polyaniline suspensions in silicone oil were investigated. In contrast to chemically polymerized polyaniline in an acidic aqueous medium by oxidation polymerization, we adopted an emulsion polymerization technique in which aniline is polymerized in an emulsion of water and a nonpolar (or weakly polar) organic solvent. The effects of electric field strength and particle concentration on the ER properties of DBSA-doped polyaniline suspensions in silicone oil were then examined. Rheological measurements were also carried out using a rotational rheometer with a high-voltage generator in both controlled shear rate and shear stress modes, and the results showed that the ER properties were enhanced by increasing the particle concentration and electric field. Received: 23 August 1999 Accepted: 6 April 2000     

Extension of the surfactant bridge model for the electrorheological effects of surfactant-activated suspensions

Surfactants influence the electrorheological (ER) response in two ways. At low surfactant concentrations, they enhance the ER response by enhancing the particle polarizability; at high concentrations, the response degrades (nonlinear ER response). The nonlinear ER behavior arises from the formation of surfactant bridges between the particles at high surfactant concentrations. A surfactant bridge model was introduced to explain the nonlinear behavior (tau0 proportional to En, n approximately 1) of surfactant-activated ER suspensions when surfactant bridges were formed between the particles. Here, the surfactant bridge model is extended for the prediction of both the linear and nonlinear ER behaviors of surfactant-activated ER suspensions over the low and high surfactant concentrations (for Brij 30, from 0 to 7 wt%), regardless of the formation of surfactant bridges between the particles. For 20 wt% neutral alumina suspensions in silicone oil activated by Brij 30, the predicted ER behaviors show almost the same Brij 30 concentration and electric field strength dependence. It predicts the linear E2 dependence of the ER response at low surfactant concentrations and the nonlinear ER behavior at high surfactant concentrations. Also, the estimated yield stresses show fairly good agreement with the experimental data.     

Electrorheological suspensions of laponite in oil: rheometry studies

We have studied the effect of an external direct current (DC) electric field ( approximately 1 kV/mm) on the rheological properties of colloidal suspensions consisting of aggregates of laponite particles in a silicone oil. Microscopy observations show that, under application of an electric field greater than a triggering electric field Ec approximately 0.6 kV/mm, laponite aggregates assemble into chain- and/or columnlike structures in the oil. Without an applied electric field, the steady-state shear behavior of such suspensions is Newtonian-like. Under application of an electric field larger than Ec, it changes dramatically as a result of the changes in the microstructure: a significant yield stress is measured, and under continuous shear the fluid is shear-thinning. The rheological properties, in particular the dynamic and static shear stress, were studied as a function of particle volume fraction for various strengths (including null) of the applied electric field. The flow curves at constant shear rate can be scaled with respect to both the particle fraction and electric field strength onto a master curve. This scaling is consistent with simple scaling arguments. The shape of the master curve accounts for the system's complexity; it approaches a standard power-law model at high Mason numbers. Both dynamic and static yield stresses are observed to depend on the particle fraction Phi and electric field E as PhibetaEalpha, with alpha approximately 1.85 and beta approximately 1 and 1.70 for the dynamic and static yield stresses, respectively. The yield stress was also determined as the critical stress at which there occurs a bifurcation in the rheological behavior of suspensions that are submitted to a constant shear stress; a scaling law with alpha approximately 1.84 and beta approximately 1.70 was obtained. The effectiveness of the latter technique confirms that such electrorheological (ER) fluids can be studied in the framework of thixotropic fluids. The method is very reproducible; we suggest that it could be used routinely for studying ER fluids. The measured overall yield stress behavior of the suspensions may be explained in terms of standard conduction models for electrorheological systems. Interesting prospects include using such systems for guided self-assembly of clay nanoparticles.     

Quasi-static electrorheological properties of hematite/silicone oil suspensions under DC electric fields

In this work, a modified rheometer has been used to gain information on the "start-up" of the shear flow of an electrorheological (ER) fluid consisting of hematite particles dispersed in silicone oil. The results show that unelectrified suspensions behave essentially as fluids, continuously deforming upon application of shear. However, this behavior changes in the presence of an electric field. For low fields and low volume fractions of solids, a solidlike (drastic increase in shear stress after the strain is applied) behavior is observed for small deformations. If the strain is increased, the yield starts and a transition to a viscoelastic-plastic nature is observed. Finally, a plastic behavior is characteristic of the post-yield regime. If the field strength and solids content are high, a discontinuous flow profile develops. These results, together with direct structural observations, suggest that the observed behavior is compatible with the formation of layers of particles electrophoretically deposited on the electrodes; the layers turn into rings when the shear field is applied. It is the slip of the fluid between these rings that can be considered responsible for the ER effect in these suspensions.     

ELECTRORHEOLOGICAL PROPERTIES OF DIATOMITE/SILICONE OIL SUSPENSIONS UNDER DC FIELDS

In this study, electrorheological （ER） behavior of suspensions prepared from 3.0 and 9.0 μm diatomite particulate, dispersed in insulating silicone oil （SO） medium was investigated. Sedimentation stabilities of suspensions （c = 5 wt%） prepared using these diatomite powders were determined to be 32 days （d = 3 μm） and 24 days （d = 9 μm）, respectively. ER activity of all the suspensions was observed to increase with increasing electric field strength, concentration and decreasing shear rate. Shear stress of diatomite suspensions increased linearly with increasing concentrations of the particles and with the applied electric field strength. Electric field viscosity of all the suspensions decreased sharply with increasing shear rate and particle size, showing a typical shear thinning non-Newtonian visco-elastic behavior. Effects of high temperature and polar promoter onto ER activity ofdiatomite/SO system were also investigated.     

Electrorheological fluid characterization via a vertical oscillation rheometer

A custom designed vertical oscillation rheometer (VOR) is used for the rheological measurements of electrorheological (ER) fluids consisting of 15 and 20 vol.% semiconducting polyaniline particles suspended in silicone oil. The viscoelastic material functions, including complex viscosity and complex shear modulus, are measured via geometric parameters, measured force, and applied strain of the VOR. Viscoelastic properties of the ER fluids are also measured as a function of applied electric field strength and particle concentration. The VOR, equipped with a high voltage generator, can easily be constructed and used to measure ER properties. It is further found that polyaniline suspensions behave as viscoelastic materials in an electric field. In linear viscoelastic conditions, elasticity was promoted with the increment of electric field due to particle chain structure in the presence of the applied electric field. It is also found that the applied electric field rather than particle concentration enhanced the elasticity of ER fluids.     

Synthesis and electrorheology of camphorsulfonic acid doped polyaniline suspensions

 Semiconducting camphorsulfonic acid doped polyaniline (PANI–CSA) particles were synthesized by chemical oxidation polymerization, and their chemical structure and particle size were examined via Fourier transform IR spectroscopy and scanning electron microscopy, respectively. Electrorheological (ER) fluids were prepared by dispersing the PANI–CSA particles in silicone oil, and their steady-shear rheological properties under electric fields were investigated using a rotational rheometer with a high-voltage generator. The PANI–CSA synthesized in this study possesses typical ER behavior:shear stress increases with increasing electric field strengths. Received: 31 August 2000 Accepted: 6 April 2001     

稀土掺杂聚苯撑ER流体的研究

选用CeCl4和FeCl3等对自制的对苯撑进行掺杂,将制得的高介电聚苯撑粉末加入到硅油中得到电流变体流体,测量了在电场作用下粘度和漏电流密度,以及相关的物理常数。讨论了电场强度、粒子浓度与粘度和漏电流密度的关系,粘度变化的响应速度和恢复时间,并探讨了其相关机制。     

Pickering emulsion polymerization of core–shell-structured polyaniline@SiO2 nanoparticles and their electrorheological response

We synthesized semiconducting polyaniline (PANI) nanoparticles through a solid-stabilized Pickering emulsion route using silica nanoparticles. Specific morphologies of the silica nanoparticle wrapped PANI particles were observed using both scanning electron microscope and transmission electron microscope, which showed the emulsifiability of silica nanoparticles in the emulsion system. Electrorheological (ER) behavior of this novel particle-based ER fluid dispersed in silicone oil was measured by a controlled shear stress rheometer and analyzed with a flow curve equation of Cho-Choi-Jhon model, which fitted well the flow curves measured in the exposed electric field.     

Linear viscoelastic properties of electro-rheological nano-suspension confined to narrow gap between electrodes

The linear viscoelastic properties of a suspension composed of titanium dioxide nanoparticles were measured under the direct current (dc) electric field with narrow gap distances between the electrodes. The yielding behavior under no external electric fields was also discussed. The wall slip at the interface between the parallel plates and the nano-suspension was briefly discussed. Under the dc electric field, a fine chain-like microstructure was optically found within a narrow gap of 50 μm between the electrodes in the quiescent state. The nano-suspension confined to a narrow gap of 65 μm between the parallel plates was rather viscoelastic even at the highest strength of the electric field of 16 kV·mm⁻¹. Furthermore, fast and slow relaxations of the dynamic moduli were found after removal of the electric field. It was pointed out that the linear viscoelasticity was an appropriate measure of the microstructure before yielding.