Electrorheological Properties Of Suspensions Research Articles

Electrorheological Fluids Based on Bismuth Ferrites BiFeO3 and Bi2Fe4O9

A comparative analysis has been made for the dielectric and electrorheological properties of suspensions of highly dispersed powders of bismuth ferrites BiFeO3 and Bi2Fe4O9 in polydimethylsiloxane PMS-300. Dielectric characteristics (dielectric constant, dielectric loss tangent) for the suspensions in frequency range 2.5–106 Hz have been determined and non-Debye character of relaxation processes in these systems has been revealed. The measured values of dielectric constant for the disperse bismuth ferrites at zero and infinite frequency (e0 and e∞) are 150 and 59 for BiFeO3, 22 000 and 14 for Bi2Fe4O9, respectively. Electrorheological properties of bismuth ferrite suspensions in static electric field (up to 5 kV) in tension, compression, and shear modes have been analyzed. It has been found that the values of electrorheological effect for BiFeO3 suspensions in polydimethylsiloxane PMS-300 are small even at high concentrations of disperse phase (60 wt %). On the contrary, the suspensions of highly disperse Bi2Fe4O9 exhibit distinct electrorheological effect. For 80 wt % Bi2Fe4O9 suspension, the tensile yield point reached ~7 kPa in electric field of 5 kV, while compressive stress was 12 kPa.

Electrorheological Behavior of Suspensions of Polyimide-Based on the Sodium Salt of 2,5-Diaminobenzenesulfonic Acid

Electrorheological suspensions (ERS) of polyimide particles with organoelement fragments from the sodium salt of 2,5-diaminobenzene sulfonic acid were obtained for the first time. Their rheological and electrorheological characteristics, their dependence on the parameters of deformation, and the intensity of the external electric field were studied. It was found that the ERS of PI-Na polyimide particles have a significant electrorheological response. Solid-polyimide materials were previously studied using a scanning electron microscope. The effect of the polyimide concentration on the properties of the solution was studied by spectrophotometry. It was shown that polyimide suspension is a result of increasing intensity as the electric field changes the flow type from Newtonian to pseudoplastic due to polarization of the particles and formation of the chain structures along the power lines of the electric field. The influence of temperature on the change of rheological and electrorheological properties of a polyimide ERS in constant electric fields was investigated.

Scale effects of the rheological properties of electrorheological suspensions

The knowledge about the rheological behavior of electrorheological suspensions in all prevalent conditions is essential for the design process of applications. Of particular importance is the dependence of fluid viscosity on the electric field strength, the temperature, and the shear rate. Previous research has pointed out the difficulties in determining the relevant rheological parameters independent from the geometry and flow conditions. For example, experimental results obtained using a capillary rheometer are different from the results gained in flow channel experiments. Even the results from one flow channel could not easily be used to predict the performance of a channel with, for example, a different distance between the electrodes. Some possible effects such as wall slip, interactions of the particles with the surface of the electrodes, or scale effects based on the particle size distribution in relation to the dimension of the flow channel may complicate the determination of the rheological parameters. To investigate these effects, a flow channel test rig that allows systematic changes to the flow conditions was developed. The distance of the electrodes can continuously be changed from 0.02 to 1 mm with an apparent shear rate from 100 to 10,000 s−1. The electrodes can easily be replaced to determine the influence of surface structure. This article will first discuss the design of the flow channel followed by the experimental results obtained under different test conditions. The aim of this research is to gain insight into the scale effects of electrorheological suspensions in order to develop microfluidic applications.

The comparison between carboxyl, amido and hydroxy group in influencing electrorheological performance

Three kinds of electrorheological (ER) materials with carboxyl, amido and hydroxyl group, respectively, were synthesized by a simple adsorption method. The powder of silicon dioxide as a substrate of the materials, as well as terephthalic acid [p-C6H4(COOH)2, abbr.: phen-COOH], p-phenylenediamine [p-C6H4(NH2)2, abbr.: phen-NH2] and hydroquinone [p-C6H4(OH)2, abbr.: phen-OH] were chosen as starting materials. The ER properties of suspensions of the materials in silicon oil were studied. The suspension of the material adsorbing phen-COOH reveals the highest ER activity, the relative shear stress of the suspension (25 wt%), τr(=τE/τ0, τE and τ0 are the shear stresses at electric field strengths of E=4.2 and 0 kV/mm, respectively), reaches 220 under a DC electric field at a shear rate of 14.5 s−1. The shear stress of the suspension of the material adsorbing phen-NH2 is the largest at an high electric field strength. The ER activity of the material adsorbing phen-OH is the lowest among the three materials. The molecule structure is an importance factor in influencing ER performance of the materials for similar compounds with different polar function groups. The relationship between the ER activity and dielectric property of the materials was discussed.

Effect of hydrophilicity of polyaniline particles on their electrorheology: Steady flow and dynamic behaviour

Electrorheological properties of suspensions are considerably affected by hydrophilicity of suspension particles. As a model material, polyaniline base powder protonated with sulfamic, tartaric, or perfluorooctanesulfonic acids provided particles of various hydrophilicity. The experiments revealed that, in the absence of electric field, due to a good compatibility of hydrophobic polyaniline particles with silicone-oil medium, their interactions were limited and the viscosity of suspension was low. When the electric field was applied, the rigidity of the polarized chain structure of the particles increased and, consequently, viscosity increased as well. In the contrast, the field-off suspension viscosity of highly interacting hydrophilic particles, which are incompatible with the oil, and where particle aggregation may set in, was high especially at low shear rates, and the material had a pseudoplastic character. Then, a relative increase in viscosity due to the polarization of the particles or their clusters in the electric field was much lower than in the former case. Due to a different primary structure of suspension, depending on the particle compatibility with the oil the field-off storage modulus of suspensions of hydrophobic particles was lower than the loss modulus, while in suspensions of hydrophilic particles the former modulus dominated. In both cases, an increase in elasticity with increasing electric field strength was higher than that in viscosity.

A new class of electrorheological material: synthesis and electrorheological performance of rare earth complexes of phosphate cellulose

A new class of electrorheological (ER) material, rare earth (RE = Ce, Gd, Er and Y) complexes of phosphate cellulose, has been synthesized using microcrystalline cellulose, phosphoric acid, urea and RE(NO3)3 solutions as starting materials. The ER properties of suspensions of microcrystalline cellulose, phosphate cellulose [cellulose-P-ONH4] and the [cellulose(-P-O)3RE] complex particle materials in silicon oil have been investigated under DC electric field. The formation of rare earth complexes helps to decrease the shear stress and viscosity at zero electric field, and to enhance the ER effect of the materials. The shear stress (τE) of the ER fluid (20% weight fraction) of a typical yttrium complex [cellulose(-P-O)3Y], the yttrium content of which is 0.04 mol/100 g, is 2.3 kPa at 4.2 kV/mm and 300 s−1 with a τr value (τr = τE/τ0, where τ0 is the shear stress at no electric field and 300 s−1) of 34.3, which is 18 times higher than that of pure microcrystalline cellulose suspensions. The improvement of dielectric loss tangent of the material, due solely to the formation of rare earth complexes, resulted in an enhancement in the ER effect of the material. In addition, the cellulose(-P-O)3RE materials possess better thermal stability, and their suspensions are more stable in the anti-sedimentation than that of the cellulose-P-ONH4 material.

Preparation and electrorheological characteristics of β‐cyclodextrin–epichlorohydrin–starch polymer suspensions

AbstractThree environment friendly β‐cyclodextrin polymer electrorheological (ER) particles (NS‐β‐CDP, WSS‐β‐CDP, and CLS‐β‐CDP) were synthesized by copolymerization through a mixture of β‐cyclodextrin (β‐CD) and epichlorohydrin in the absence of starch or in the presence of water‐soluble and water‐insoluble starch, respectively. The electrorheological properties of suspensions in silicone oil were then investigated under direct current (dc) electric fields. It was found that the yield stress of the typical WSS‐β‐CDP ER fluid was 6.2 kPa in 4 kV/mm, which is 35% higher than that of NS‐β‐CDP and similar to that of CLS‐β‐CDP. In the meantime, it can display a high ER performance even over a range of 65–95°C. The structures of these polymers were characterized by FT‐IR and Raman spectrometry, respectively. The results demonstrated that all of these polymers keep the original structural character of β‐CD and the copolymerizations between starch and β‐CD indeed occur. Furthermore, it was found that there was some relationship between the characteristic strength of polymers and their dielectric properties. Hence, the improvement of copolymer dielectric properties resulted in the enhancement of ER effects. © 2004 Wiley Periodicals, Inc. J Appl Polym Sci 93: 1681–1686, 2004

Electrorheological properties of chitin suspensions

Electrorheological suspensions are suspensions of solid particles whose rheological behavior can be strongly modified by the application of an electric field. In this article, the electrorheological properties of suspensions containing chitin particles (and its derivative-carboxylmethyl chitosan particles) in silicone oil are reported for a range of suspension weight concentrations, applied field strengths, shear rates, etc. In these suspensions, glycerin was used as an activator. The adsorbed amount of glycerin, one of the electrorheological parameters, was also studied experimentally. The ER effect of the chitin suspension reaches the maximum at about 11% of weight concentration. The dependence of the experimentally determined dynamic yield stress on particle concentration and field strength is found to be similar to that reported for other systems. The dynamic yield stress is found to increase with the particle concentration and the applied electric field strength.

Electrorheological properties of suspensions containing nonaqueous additives under high temperature condition

The electrorheological (ER) properties of cellulose suspensions which include nonaqueous polar materials as active additives for ER effect were studied comparing with water‐activated suspension. The nonaqueous polar materials are alcohols, amides, and amines from the viewpoints of dielectric constant and vapor pressure. The ER properties of these suspensions were measured with a cylindrical rheometer at temperatures up to 120 °C. Also storage stability at 120 °C was investigated. The nonaqueous additives were effective to activate cellulose suspension: Especially at higher temperatures, the nonaqueous additives were more effective than water was. The shear stress of the water‐activated ER fluid decreased as the temperature increased. On the contrary the shear stress of the ER fluids, which contain the nonaqueous additives, increased as the temperature increased, and became greater than that of the water‐activated ER fluid at room temperature. Furthermore the nonaqueous additives had advantages of decreasing the electric power consumption and of improving thermal stability of shear stress after the storage for 250 h at 120 °C.

Electrorheological Properties of Suspensions Containing Nonaqueous additives Under High Temperature Condition

The electrorheological (ER) properties of cellulose suspensions which include nonaqueous polar materials as active additives for ER effect were studied comparing with water‐activated suspension. The nonaqueous polar materials are alcohols, amides, and amines from the viewpoints of dielectric constant and vapor pressure. The ER properties of these suspensions were measured with a cylindrical rheometer at temperatures up to 120 °C. Also storage stability at 120 °C was investigated. The nonaqueous additives were effective to activate cellulose suspension: Especially at higher temperatures, the nonaqueous additives were more effective than water was. The shear stress of the water‐activated ER fluid decreased as the temperature increased. On the contrary the shear stress of the ER fluids, which contain the nonaqueous additives, increased as the temperature increased, and became greater than that of the water‐activated ER fluid at room temperature. Furthermore the nonaqueous additives had advantages of decreasing the electric power consumption and of improving thermal stability of shear stress after the storage for 250 h at 120 °C.

The electrorheological properties of polyaniline suspensions

The electrorheological properties of suspensions containing polyaniline particles in silicon oil are reported for a range of suspension volume fractions, applied field strengths, shear stresses, and particle dielectric constants. Suspension viscosity at a fixed stress is found to increase slowly as the field strength is raised to a value of E∗. Over a very narrow field strength range near E∗ the suspension viscosity is found to increase 10 6–10 8 Pa s. At field strengths greater than E∗, the suspensions take on solid-like behavior. The scaling of yield stress on volume fraction and field strength is similar to that reported on other systems and the yield stress is found to increase monotonically with particle dielectric constant.