Zero-field Viscosity Research Articles

Temperature effect of electrorheological fluids based on polyaniline derived carbonaceousnanotubes

Nitrogen-enriched carbonaceous nanotubes (N-CTs) were prepared by the carbonization ofpolyaniline (PANI) nanotubes in vacuum and were demonstrated to possess goodelectrorheological (ER) performance. In this paper, the temperature dependence of the ERproperties of the suspension composed of N-CTs in silicone oil was systematicallyinvestigated by steady shear viscosity and dynamic viscoelastic measurements. Theseshowed that under electric fields the N-CT suspension showed good temperature stabilityof its ER properties though its zero-field viscosity decreased with elevated temperatures.Meanwhile, the flow curve of shear stress versus shear rate also maintained a stable leveland the critical shear rate shifted towards high values as the operating temperatureincreased. The dynamic viscoelastic measurement showed that the storage modulus slightlyincreased with increasing operating temperature, also confirming the good temperaturestability of the ER properties of the N-CT suspension. The dielectric spectra of the N-CTsuspension and the dielectric parameters calculated by the Cole–Cole equation couldexplain the temperature dependence of the ER properties of the N-CT suspension.

Characterization and effectiveness of ER fluids: An attempt to unify methods and criteria

This paper concerns a proposal to define a way to evaluate the effectiveness of ER fluids. After recalling the basic parameters of the ER fluids: static yield stress τy, current density j, and zero-field viscosity η0, we determine for a lot of ER suspensions the experimental values of two corresponding parameters E1 = τy / j and E2 = τy / η0, and thereafter of a global effectiveness parameter En = E1E2. We also compare the results obtained in the different cases of micrometer-sized and nanometer-sized particles-based ER fluids.

BEHAVIOR OF MR FLUIDS AT HIGH VELOCITIES AND HIGH SHEAR RATES

The objective of this work is to characterize the performance of MR fluid at high shear rates and high velocities. A slit-flow rheometer has been built which allows for high speed testing of MR fluid under varying field strengths. Fluid velocities range from 3.9 m/s to 27 m/s with resulting shear rates ranging from 0.23×105 s -1 to 1.6×105 s -1. In order to evaluate the performance of the fluid, the force required to drive the fluid through the slit is measured and force-velocity characteristics are generated. The zero-field viscosity is found and results indicate that shear thinning is still present even at these high shear rates. Two magnetic field strengths were considered for the field testing (50 kA/m and 100 kA/m). Results indicate that a yield stress is still being developed in the fluid. However, as fluid velocity increases, the yield stress being developed in the fluid decreases. This reduction in the yield stress could be attributed to the dwell time, or the amount of time the fluid spends in the presence of a magnetic field.

Magnetic properties of self-organized L1 0 FePtAg nanoparticle arrays

The magnetic properties of chemically synthesized high anisotropy L1 0 [Fe 49Pt 51] 88Ag 12 nanoparticle arrays have been studied as a function of annealing temperature. Particles were prepared by the simultaneous polyol reduction of platinum acetylacetonate and silver acetate and the thermal decomposition of iron carbonyl, yielding monodispersed particles of diameter ∼3.5 nm. Addition of Ag lowers the ordering temperature of self-assembled arrays by ∼150°C. After annealing at T a=500°C for 30 min in an Ar/H 2 atmosphere, the coercivity was 13,800 Oe. TEM and delta- M measurements indicate weak particle aggregation up to T a=400°C, with evidence of sintering at higher temperatures. Large ratios of remanent to hysteresis coercivity indicate a large distribution in anisotropy energies. Anomalously large thermal stability constants, KV/ k B T, and switching volumes were measured, even in samples with very little evidence of sintering. Zero field viscosity versus remanence curves show evidence of exchange interactions.

Zero field viscosity in magnetic thin films and tapes

We have measured the relaxation of the remanent magnetization in a number of granular thin films in which delta-M measurements suggest the presence of exchange coupling. The relaxation measurements were made at zero field after application of a saturation field followed by a reverse field. The films had varying compositions (CoPtCrB, Co/CN, CoPt/SiO/sub 2/) and had thermal stability factors, KV/k/sub B/T, ranging from 29 to 670. The most general behavior of the zero field relaxation, observed for the smaller thermal stability factors, was an initial increase in the remanent magnetization followed by a decrease at longer times. The maximum initial zero field viscosity is strongly correlated with the inverse thermal stability factor, k/sub B/T/KV, and generally increases with the area under delta-M curve, normalized by the remanent coercivity. A small zero field relaxation was also observed in barium ferrite and CrO/sub 2/ tapes.

Dispersion Stability and Electrorheological Properties of Polyaniline Particle Suspensions Stabilized by Poly(vinyl methyl ether)

In the present article, a novel method of stabilization of a semi conductive polyaniline particle nonaqueous suspension of electrorheological (ER) materials was introduced. Using as the steric stabilizer poly(vinyl methyl ether) (PVME), a dispersion polymerization of aniline was performed and stable aqueous dispersions of the polyaniline were obtained. However, a stable colloidal suspension of polyaniline in silicone oil medium can be obtained only with a low concentration of PVME (0.75%), although the average size of the individual, redispersed particles in oil generally decreased with increasing concentration of PVME. At higher concentrations of PVME, formation of highly packed particle aggregates was investigated, as seen in the scanning electron microscopy images. The polyaniline suspension stabilized by 0.75% PVME content exhibited the best dispersing state and, therefore, showed the highest zero-field viscosity. Such a well-stabilized polyaniline suspension also showed the maximum ER property, namely the largest normalized yield stress in an electric field.

Electric effects on the rheology of insulating oils in electrodes with flocked fabric

The rheological behavior of insulating oils is studied in nonuniform electric fields which are generated by an electrode covered with flocked fabric. Although the oils show no electrorheological effects in uniform fields between metal electrodes with smooth surfaces, the flocked fabric leads to a striking increase of viscosity in steady shear. The viscosity enhancement increases with decreasing zero-field viscosity and decreasing conductivity of oils. In the limit of zero shear rate, the oils with low conductivity behave as solids with yield stress. When a very small quantity of fine particles is introduced into electrified oils without shear, a rapid and large-scale motion of particles is observed between the tips of fibers and the plate electrode. The local motion of fluids in high electric fields is referred to as electrohydrodynamic (EHD) convection. Periodic patterns of circulation flow are formed in static oils. The electric energy which is dissipated during the circulation motion contributes to holding the periodic flow in static oils. When the stress is very low, the periodic patterns are not broken down. The yield stress corresponds to the force required to rupture the domain structures of EHD convection. In shear fields, the additional energy may be required to change the periodic patterns of EHD convection. The striking increase of viscosity in steady shear can be attributed to the interactions between EHD convection and external shear.

ER Suspensions of Sulfonated Poly(Styrene-CO-Divinylbenzene) Particles

Two ER suspensions (ERF1 and ERF2) containing highly sulfonated poly(styrene-co-divinylbenzene) particles (ERP) were newly prepared. The ERP concentration was 20 wt% in ERF1 and 40 wt% in ERF2. The ER properties of the suspensions were investigated in view of applications to practical devices. The investigated properties were zero-field viscosity, dispersion stability, induced shear stress, current density, response time, shear rate and temperature dependence of the induced shear stress and current density, response time, shear rate and temperature dependence of the induced shear stress and the current density. electrical durability. In the results, it was found that ERF1 and ERF2 had a very high potential for practical applicatons. The remarkable characteristic of ERF1 was the very low zero-field viscosity of 35 mPa·s at 25°C. The remarkable characteristic of ERF2 was very large induced shear stress and under applying DC 4 kV/mm at 25°C, the induced shear stress was 5.1 kPa. As an application example, the ERFs can be efficiently used for an ER Cutting Machine incorporating variable speed rodless cylinders. The machine has worked smoothly for one and a half years, although the characteristic of control slightly changed.

ER Properties of a Suspension of Polymer Graft Carbon Black Particles

We newly developed ER particles with sub-micron size. The particle was polymer graft carbon black (GCB1) composed of carbon black particles and a polymer. The average particle size of GCB1 was found to be 81 nm. An ER suspension (ER1) was obtained by mixing GCB1 (30 wt%) with silicone oil (70 wt%). The ER1 showed excellent dispersion stability. Further, GCB1 particles did not settle under centrifuging at 9000G. The zero-field viscosity was 80 mPa·s at 25°C. The kinetic friction coefficient of ER1 was 0.15, while that of the silicone oil used was 0.23. When the electric field of 3 kV/mm (AC 1000 Hz) at the temperature of 25°C and the shear rate of 700 s -1 was applied to ER1, the shear stress of 116Pa was induced. The induced shear stress did not change for a long period of time period. In the temperature range between 25 and 150°C the induced shear stress and the current density were almost constant at any electric field. When 3 kV/mm (AC 50Hz) at 25°C and 700s-1 was applied to ER1, the shear stress of 88Pa was induced but the deviation of the induced shear stress from the average value was pluses and minuses 3 Pa.

ER Fluids Based on Liquid-Crystalline Polymers

Electrorheological (ER) fluids are most broadly classified as either particle dispersion or homogeneous types. The history of their development has been one of a search for fluids of either type that exhibit a large ER effect—an increase in viscosity or shear stress upon exposure to an electric field—together with longterm stability under various temperatures and conditions of use.The first particle dispersion ER fluids were invented by W.M. Winslow in the late 1940s. Many fluids of this type have been investigated since then, and a few have been developed and adopted for practical applications.Homogeneous ER fluids have been investigated even longer. The earliest reported observations of the ER effect were for homogeneous fluids composed of glycerin and paraffin oil in the 1890s. In the 1930s, the ER effect was also observed in polar liquids such as nitrobenzene and anirin and in colloids of superfine metal powders. In all cases however the viscosity in the electric field was only two or three times the zero-field viscosity, which is too small for useful applications.Since the advent of low-molecular-weight liquid-crystalline (LC) materials in the 1960s, investigations have been made on the viscosity changes accompanying their inherent tendency to align in an electric field, but their maximum viscosity generally is only a few times their zero-field viscosity, and their shear stress is in any case small.

THE DEVELOPMENT OF ELECTRORHEOLOGICAL FLUIDS FOR AN AUTOMOTIVE SEMI-ACTIVE SUSPENSION SYSTEM

The feasibility of electrorheological (ER) dampers for an automotive semi-active suspension was evaluated in a three phase program. In the first phase, ER fluid performance targets were derived. The desired ride and handling attributes of the suspension system were translated into damper specifications, which were then translated into the ER fluid performance targets. The damper specifications included dynamic range, bandwidth, power draw, and packaging. The ER fluid performance parameters then included zero-field viscosity, ER stress, response time, and power density. In the second phase, the dampers and the ER fluid were developed to meet the performance targets. Trade-offs were made between damper design and fluid formulation to achieve the desired damper dynamic range and power draw. A state-diagram approach using screen test data was used to select candidate ER fluids. In the third phase of the program, a prototype semi-active suspension system using fast, continuously variable ER dampers was installed on a demonstration vehicle. Heave, pitch, and roll motions of the vehicle were controlled by applying voltages independently to the four dampers as determined by a modified sky-hook algorithm. The system was designed to respond in less than 10 ms with an average power requirement less than 40 W for normal road surfaces and handling. Laboratory data from a pressure driven flow screen test and a damper test are presented that document the ER fluid performance specification and selection process. Vehicle performance data are presented that demonstrate the features of ER technology for the semi-active suspension application. Remaining issues for commercialization of ER fluids are discussed.

CONTROLLABLE FLUIDS: THE TEMPERATURE DEPENDENCE OF POST-YIELD PROPERTIES

This paper represents the first detailed description of the affect of temperature on the properties exhibited by state-of-the-art electrorheological (ER) and magnetorheological (MR) fluids. In particular, shear stress versus shear strain rate curves, dynamic and static yield stress values, zero-field viscosity data, and current density measurements are discussed. Specific comments concerning the stability of both mechanical and electrical properties over broad temperature ranges are provided. Finally, insight into the advantages associated with using electrorheological and magnetorheological fluids in a controllable device is provided.

Electrorheological properties of barium titanate suspensions under oscillatory shear

The electrorheology of suspensions composed of barium titanate particles, silane coupling agent, water, and silicone oil was studied by the use of an oscillating plate rheometer. The magnitude of the complex viscosity, |η*|, rapidly increases on the application of electric fields and the suspenstions change from viscous liquids to solid-like pastes. Significant flow occurs only after a yield stress is exceeded. Because the addition of water contributes to the development of yield stress and the silane coupling agent leads to a decrease of |η*| in the absence of electric fields, the electrorheological performance characterized by the balance between the yield stress under electric fields and the zero-field viscosity is markedly improved by a superposition effect of additives. The rapid response can be directly related to the increase in particle-particle attraction, rather than the migration and structural formation of particles. The polarization of adsorbed substances may be primarily responsible for the electrorheological effect.