Dielectric electrorheological fluids: Theory and experiment (original) (raw)

An experimental investigation of the dielectric properties of electrorheological fluids

Smart Materials and Structures, 2009

A home-made electrorheological (ER) fluid, known as ETSERF, has been created with suspension-based powders dispersed in silicone oil. Because of the special structure of their particles, ETSERF suspensions present a complex behavior. In the absence of an electric field, the ETSERF fluid manifests a near-Newtonian behavior, but when an electric field is applied, it exhibits a pseudoplastic behavior with yield stress. The ER effect under DC electric fields has been experimentally investigated using both hydrous and anhydrous ER fluids. The ER properties are strongly dependent on the dielectric properties of ETSERF suspensions, and hydrous ER fluids have a high dielectric constant and a high relaxation frequency which show a strong electrorheological effect. The relationship between the electrorheological effect and the permittivity of ER fluids has also been extensively studied. Experimental results show that the interfacial polarization plays an important role in the electrorheological phenomenon. The ageing of ETSERF fluids was also studied and it was found that the dielectric properties (mainly the dielectric loss tangent) and ER properties are strongly related to the duration of ageing. A fresh ETSERF suspension exhibits high relaxation frequency and high dielectric constant. These results are mainly explained by the effect of interfacial polarizations.

Rheological and dielectric behavior of electrorheological emulsions

Colloids and Surfaces A: Physicochemical and Engineering Aspects, 2004

The rheological and dielectric behavior of electrorheological (ER) emulsions composed of silicone oil (continuous phase) and two chlorinated paraffins (dispersed phase) are studied in this work. The chlorinated paraffins have different permittivity and conductivity values, and both are more conducting than the silicone oil. The rheological behavior of the emulsions is analyzed under constant dc electric fields, for two chlorinated paraffin concentrations. Results reveal that the magnitude of the ER response in the emulsions increases with the applied voltage but is affected negatively by the concentration of the chlorinated paraffin. The growth of viscosity in the presence of the electric field is less significant in the system with the largest conductivity at high electric fields. At low concentration, a Maxwell-Wagner polarization mechanism (interfacial polarization) is observed. A relationship between the dielectric and ER behavior is established, and also between the microstructural changes in the emulsions and their rheological and dielectric properties.

Structure of electrorheological fluids: A dielectric study of chain formation

Physical Review E, 2012

A dielectric measurement method has been proposed to apply to the study of the microstructure of electrorheological (ER) fluids. To test our measurement method the dielectric permittivity increment caused by pair and chain formation was measured in dilute Brownian ER fluids composed of silicone oil and nanosized silica particles. The critical values of the electric field required to induce structure formation were experimentally determined from the electric field dependence of the measured permittivity increment. From the electric field induced time evolution of the relative permittivity of ER fluids, the characteristic times of the pair and chain formation were calculated. Our experimental results for the time constants are in good agreement with the corresponding theoretical data obtained from the Eyring theory.

The Effect of Temperature and Electric Field on the Behavior of Electrorheological Fluids

An Electrorheological (ER) process occurs when the viscosity of fluid with dispersed particles is modified by the application of an electric field. The Electrorheological flowable dispersed fluids can be currently used for fixing of materials responding to mechanical loads and, as working media for dampers and dielectric actuators. The present investigation has been undertaken with the aim of studying the parameters that effect on the apparent viscosity of low–concentration ER-fluid (diatomite in transformer oil). Results demonstrate increases in the viscosity by applying electric field. It is shown that the viscosity behavior can be reasonably modeled as a power–low fluid, with the viscosity equal to a consistency index, K, multiplied by the shear rate raised to the power n-1. Results indicate that both the consistency index K and the exponent n are influenced by voltage and temperature, where K has linear and n has exponential relation with temperature. The variation of the appare...

Electrorheological fluid under elongation, compression, and shearing

Physical Review E, 2002

Electrorheological ͑ER͒ fluid based on zeolite and silicone oil under elongation, compression, and shearing was investigated at room temperature. Dc electric fields were applied on the ER fluid when elongation and compression were carried out on a self-constructed test system. The shear yield stress, presenting the macroscopic interactions of particles in the ER fluid along the direction of shearing and perpendicular to the direction of the electric field, was also obtained by a HAAKE RV20 rheometer. The tensile yield stress, presenting the macroscopic interactions of particles in the ER fluid along the direction of the electric field, was achieved as the peak value in the elongating curve with an elongating yield strain of 0.15-0.20. A shear yield angle of about 15°-18.5°reasonably connected tensile yield stress with shear yield stress, agreeing with the shear yield angle tested well by other researchers. The compressing tests showed that the ER fluid has a high compressive modulus under a small compressive strain lower than 0.1. The compressive stress has an exponential relationship with the compressive strain when it is higher than 0.1, and it is much higher than shear yield stress.

Electrorheological Fluids: Properties, Technology and Modern Applications

IRJET, 2022

Since last three decades, ER fluid has major importance in science, medical and engineering problems, which include vibration reduction and suspension. Electrorheological fluids are smart materials whose rheological properties are controllable through the applications of an external electric field. These rheological properties of ER fluid can be exploited in ERF devices for advanced technological applications. The optimal design of ERF devices requires proper mathematical modeling and basic governing equations. This paper presents the working principles, governing equations and mathematical framework for ER fluids. Also in this paper recent progress of ER devices and their applications have been discussed.

Dynamic dielectric response of electrorheological fluids in drag flow

Physical Review E, 2015

We have determined the response time of dilute electrorheological fluids (ER) in drag flow from the dynamic dielectric response. On the basis of a kinetic rate equation a new formula was derived to approximate the experimental time-dependent dielectric permittivity during the temporal evolution of the microstructure. The dielectric response time was compared to the standard rheological response time extracted from the time-dependent shear stress, and a good agreement was obtained. We found that the dielectric method is more sensitive to detect any transient during the chain formation process. The experimental saturation value of the dielectric permittivity corresponding to the equilibrium microstructure was estimated on the basis of formulas derived from the Clausius-Mossotti equation.

Rheo-dielectric effect in liquid suspensions

Philosophical Magazine, 2009

A rheo-dielectric effect, dielectrostriction, relates the polarizability of a material to its deformation. Stress, strain, strain rate or some combination of these parameters could be the state variables for a given material. The description of the dielectrostriction in isotropic materials involves two material coefficients. A key advantage of the presented experimental technique is the utilization of a single deformation mode, shear deformation, for two independent measurements of the material coefficients in liquid suspensions. The study is conducted with micro-and nano-sized alumina oxide (Al 2 O 3) particles dispersed either in silicone oil (Newtonian fluid) or in liquid silicone elastomer (viscoelastic fluid). The dielectrostriction response of each suspension is compared with those of the corresponding base liquids. The selection of strain or stress as the state variable of deformation is discussed. Material coefficients for both the strain-and stress-based descriptions are presented for each system.

Response time in electro-rheological fluids as a function of dielectric constant and viscosity

Physica A-statistical Mechanics and Its Applications, 1996

Response times of a number of Electro-Rheological Fluids (ERF's) produced with silica particles and various liquid phases with different viscosities and dielectric constants, were optically measured through a specifically-designed set up. The analysis of the data shows that for all the experimental results, t (delay time) is proportional to 1/Ea, where E is the applied electric field and a an