Negative Electrorheological Effect Research Articles

An energy perspective on the mechanism of crude oil electrorheological effect

Exposing a waxy crude oil to an electric field represents an emerging environmentally sound strategy for improving the cold flowability of oil. However, a substantial knowledge gap still exists regarding the quantitative relationship between the viscosity reduction and treatment parameters (field strength, treatment time, the volume of treated oil, etc.). This study endeavors to investigate the physical essence of the effect of these treatment parameters on the viscosity reduction and its duration. It was found when subjected to electric fields of varying strengths (0.5–5 kV/mm) for sufficient time, a same maximum viscosity reduction of approximately 40% can be achieved regardless of the applied field strength. Further research has elucidated that the factor determining the viscosity reduction is energy input, rather than the field strength as was reported previously, and the inputted energy may work in three stages: first, it works for initiating a decrease in viscosity. Subsequently, the continued energy input further reduces the oil viscosity and ultimately achieves a maximum reduction at that temperature. Then further inputted energy enhances the duration of the viscosity reduction. Fundamentally, the inputted energy density, i.e., the inputted energy per unit volume/mass of the oil, is the essential factor. These new findings facilitate further understanding of the negative electrorheological effect and its mechanism of crude oil and may help for the development of electric treaters for reducing crude oil viscosity.

Surfactant-Switched Positive/Negative Electrorheological Effect in Tungsten Oxide Suspensions.

The electrorheological (ER) effect was experimentally observed in dielectric suspensions containing tungsten oxide (WO3) modified with surfactant molecules (sodium dodecyl sulfate (SDS) and dodecylamine (DDA)) in electric fields up to several kilovolts per millimeter. The dielectric properties of WO3 suspensions in silicone oil were analyzed, depending on the frequency of the electric field, in the range from 25 to 106 Hz. Unmodified WO3 suspensions, as well as suspensions modified with sodium dodecyl sulfate, were shown to exhibit a positive electrorheological effect, whereas suspensions modified with dodecylamine demonstrated a negative electrorheological effect. The quantitative characteristics of the negative electrorheological effect in the strain–compression and shear regimes were obtained for the first time. Visualization experiments were performed to see the chain structures formed by WO3 particles modified with sodium dodecyl sulfate, as well as for dynamic electroconvection in electrorheological fluids containing WO3 modified with dodecylamine. The negative electrorheological effect was shown to be associated with the processes of phase separation in the electric field, which led to a multiplicative effect and a strong electroconvection of the suspension at field strengths above 1 kV/mm.

Switching between negative and positive electrorheological effect of g-C3N4 by copper ions doping

Investigation of pristine g-C3N4 and copper ions doped g-C3N4 as dispersed phases in silicone-oil based electrorheological (ER) fluids is reported for the first time. Pristine g-C3N4 was prepared via standard thermal polycondensation of urea. Introduction of Cu ions into g-C3N4 polymeric network was performed by treatment of pristine powder by a solution containing tetraammoniumdiaquacopper(II) complex ions followed by annealing. The structure and properties of products were revealed with the aid of XRD, FTIR, UV–Vis and XPS, and complemented by SEM investigation of morphology, pycnometry, BET analysis, and conductivity measurements. The response of prepared ER fluids to an external electric field was examined by rheometry and the effects visualized with optical microscopy. While ER fluids based on g-C3N4 exhibited negative ER effect (decrease in viscosity when the field is switched-on), ER fluids based on a g-C3N4/Cu-doped analogue exhibited positive ER effect. Dielectric spectroscopy using Havriliak-Negami model revealed that introduction of the dopant almost doubled the dielectric relaxation strength while the relaxation time was halved. The ability of g-C3N4/Cu as a candidate for further studies necessary to increase the ER effect was demonstrated. Thereto, described modification of g-C3N4 by copper ions shall be applicable also for other metals forming ammonia complexes.

Electrorheological response of polyindene/colemanite conducting composite

In this study, electrorheological (ER) responses of colemanite and polyindene (PIn)/colemanite conducting composite dispersions in silicone oil (SO) were investigated. Antisedimentation ratios of the dispersions were determined. Some parameters which affect the ER properties of the dispersions such as electric field strength (E), shear rate, frequency and temperature were investigated. The rather unusual behavior known as "negative ER effect" was observed for colemanite/SO above E = 1.5 kV/mm and for PIn/colemanite/SO under all the values of electric field strength at volume fraction of 25%. This negative ER response was converted to positive with the addition of non-ionic surfactant.

Positive and Negative Electrorheological Response of Alginate Salts Dispersed Suspensions under Electric Field

Electrorheological (ER) effects of alginic acid and alginate salts (Na(+) alginate, NH(4)(+) alginate, and Ca(2+) alginate) dispersed suspensions were investigated under DC electric fields. A noteworthy result is that the Ca(2+) alginate dispersed suspension showed negative electrorheological effects under electric fields while the other suspensions exhibited positive electrorheological effects. It is the first time that the negative ER effect is obtained with the biomacromolecule. Interestingly, at the DC electric fields, the electromigration of particles to two electrodes was observed in the negative ER fluid, while the particles-bridges formed between two electrodes in the case of the positive ER fluid. In conclusion, the specific salt type of biomacromolecules could be suitable ER particles for negative ER suspension. We believe that our study can present a new way for the development of the biocompatible and eco-friendly negative ER fluids.

The negative and positive electrorheological behavior and vibration damping characteristics of colemanite and polyindene/colemanite conducting composite

In this study, the electrorheological (ER) properties of colemanite and polyindene (94.8% PIn)/colemanite (5.2%) conducting composite were investigated by dispersion in silicone oil (SO). The zeta (ζ)-potentials and antisedimentation ratios of the materials were determined. Some parameters which affect the ER properties of all the dispersions such as the volume fraction, electric field strength (E), shear rate, frequency and temperature were investigated. The rather unusual behavior known as the negative ER effect was observed for colemanite/SO above E = 1.5 kV mm−1 and for PIn/colemanite/SO under all values of the electric field strength even at high volume fraction. This negative ER response was converted to a positive one by the addition of non-ionic surfactant. Furthermore, glycerol was used as a polar promoter and observed to enhance the ER activity of the colemanite/SO system. Creep-recovery tests were applied to all the dispersions studied to investigate their behavior under sustained shear stress. Finally, 28% and 30% vibration damping capacities were achieved using an automobile shock absorber for the glycerol/colemanite/SO and non-ionic surfactant/PIn/colemanite/SO systems under the E = 0.17 kV mm−1 condition, respectively.

Effect of surface properties on the electrorheological response of hematite/silicone oil dispersions

In this work we present an investigation of the influence of particle surface characteristics on the electrorheological (ER) behavior of suspensions of either pure or modified hematite (α-Fe2O3) particles dispersed in silicone oil. The modification consisted of either dehydration or hydrophobization of the particles before preparing the suspensions. A comparison was performed between the electrorheological responses of suspensions with the same volume fraction of hematite particles having different surface properties. The effects of applied electric field strength on the viscosity, yield stress and dynamic moduli of these suspensions were examined. It was found that the usual positive ER response, that is, enhanced values of the yield stress and elastic modulus induced by the electric field were obtained for hematite and, to a lesser extent, for dried hematite suspensions. In contrast, a “negative ER effect”, i.e., the reduction of yield stress and elastic modulus upon application of electric field was observed for hydrophobically modified (oleic acid coated) hematite. This means that the field produces destruction of structures rather than their build up, above a threshold electric field strength.

Negative Electrorheological Behavior in Suspensions of Inorganic Particles

An investigation is described on the electric-field-induced structures in colloidal dispersions. Both rheological determinations and direct microscopic observations are used with that aim. The starting point of this study is the so-called electrorheological (ER) effect, consisting of the mechanical reinforcing of a fluid or suspension due to formation of chains of molecules or particles after being polarized by the action of the field. One macroscopic manifestation of this phenomenon is the transformation of the fluid from a typically Newtonian behavior to a viscoelastic material, with finite yield stress and high elastic modulus. The systems investigated were suspensions of elongated goethite (β-FeOOH) particles in silicone oils with varying amounts of silica nanoparticles. The results showed the rather unusual behavior known as "negative ER effect", which can be best described by saying that the application of an electric field reduces the yield stress and the elastic modulus, that is, produces destruction of structures rather than their build up. The negative behavior is also found for suspensions of other inorganic powders, including hematite and quartz. On the contrary, the usual positive ER response is found for suspensions of cellulose and montmorillonite clay. The same happens if goethite suspensions are prepared in high volume fractions, high-viscosity fluids, or both. All of the results found are compatible with the so-called interfacial model of electrorheology: the reduction of the yield stress of goethite suspensions when the applied field is high enough is the consequence of particle migration toward the electrodes because of charge injection and subsequent electrophoresis. The migration leaves the gap between the electrodes devoid of particles and explains the decrease in yield stress. The addition of silica nanoparticles contributes to reduce the strength of this effect by hindering the charging and making it necessary to increase the field strength to observe the negative effect. The model appears to also be applicable to cellulose, although the positive response found for such particles is explained by their large size: larger diameters bring about larger attraction forces between particles, leading to a tendency to produce strong aggregates. This is likely to occur in suspensions of colloids which, because of their relatively high electrical conductivity, tend to acquire charge even in such nonpolar liquids as silicone oils.

Dynamics simulation of electrorheological suspensions in poiseuille flow field

Based on a modified Maxwell-Wagner model, molecular dynamics is carried out to simulate the structural changes of ER (electrorheological) suspensions in a poiseuille flow field. The simulation results show that the flow assists in the collection of particles at the electrodes under a low pressure gradient, and the negative ER effect will show under a high pressure gradient. By analyzing the relationship curves of the shear stress and the pressure gradient in different relaxation time, it is found that for the same kind of ER suspensions materials, there is an optimal dielectric relaxation frequency.

Electro-Rheological Response of Liquid Crystals under Oscillatory Squeeze Flow

We have investigated the electro-rheological (ER) properties of liquid crystals in an oscillatory squeezing flow. A Micro Fourier Rheometer was utilized to estimate the complex viscosity and phase shift. A clear dip in the phase angle was observed, centred around a frequency which increased with electric field strength. It was found that this critical frequency was proportional to the inverse of the response time required for the liquid crystal molecules to align under the electric field. Similar ER effects to those observed under steady shearing were obtained in the oscillatory flow, but the ER effect at high frequency is smaller than that under no electric field. In other words, a negative ER effect was obtained under low electric fields. A rheological model for the dynamic response was obtained through the control theory and the transfer function thus derived will be useful for estimating the output response in a flow or motion control system.

Electrorheological response of swollen silicone gels containing barium titanate

We have investigated storage moduli of silicone gels containing barium titanate in the presence of dc electric fields. The gels containing barium titanate swollen by silicone oil showed a storage modulus reduction, i.e. negative electrorheological effect. Contrary, no negative electrorheological effect was observed in the unswollen gels and silicon gels without barium titanate. Swollen silicone gels and most of silicone/BaTiO 3 gels obeyed empirical quadratic dependence in electric field strength. Although an apparent phase separation was not observed in the swollen gel, microscopic phase separation may occur due to the difference in electric conductivity between particles (∼10 −10 S/cm) and silicone oil (10 −9 S/cm), as a result, the negative electrorheological effect appears. The effects of frequency, degree of swelling, and the field strength have been discussed.

Negative Electrorheological Effect of Silicone Gels Containing Barium Titanate

AbstractSummary: We observed the negative electrorheological phenomenon on swollen silicone gels containing barium titanate. Contrary, no negative electrorheological effect was observed in unswollen silicone gels containing barium titanate and silicon gels without barium titanate. The change in storage modulus increased with increasing DC electric field strength. The effects of frequency, degree of swelling, and the field strength have been investigated.Electric‐field dependence of the change in storage modulus at f = 0.1 Hz for swollen silicone/BaTiO3 gels with varying CAT content; (○): CAT 0.1, (□): CAT 0.2, (⋄): CAT 0.3, (×): SG.imageElectric‐field dependence of the change in storage modulus at f = 0.1 Hz for swollen silicone/BaTiO3 gels with varying CAT content; (○): CAT 0.1, (□): CAT 0.2, (⋄): CAT 0.3, (×): SG.

Rheological responses of oil-in-oil emulsions in an electric field

In the present article, the rheological responses of oil-in-oil emulsions in a dc electric field were investigated experimentally. Specifically, the dispersed phase of the emulsions considered in this work was less conducting than the continuous phase. Depending on the relative strength between the shear flow and electric fields, three distinctive responses of the emulsions were observed in steady and dynamic oscillatory shear tests. First, the apparent viscosity enhancement (positive electrorheological effect) was produced when the electric field was predominant. Second, when the shear flow was strong and dominant, the electric field played a trivial role on the rheological behavior of emulsions. Finally, the viscosity reduction (negative electrorheological effect) was generated when the shear flow and electric fields were competitive. The viscosity enhancement was induced by the formation of chain-like microstructures of the dispersed droplets as in a typical electric-field responsive particle suspension. Meanwhile, the viscosity reduction was closely associated with the electric-field-induced rotation of the dispersed droplets, which was confirmed by the electrohydrodynamics of a single conducting drop in a more conducting ambient fluid. Finally, the rheological responses of the model emulsions to a dynamic small-amplitude oscillatory shearing were considered in conjunction with the morphology evolution under the action of the electric and flow fields. The results showed that the interfacial contribution to the rheological response appeared quite differently depending on the conductivity ratio of the two contiguous fluids.

Rheological Behavior of Poly(methyl methacrylate) Dispersions Stabilized by a Diblock Copolymer. 2. Positive and Negative Electrorheological Effect

Rheological Behavior of Poly(methyl methacrylate) Dispersions Stabilized by a Diblock Copolymer. 2. Positive and Negative Electrorheological Effect

Dielectric Criteria for the Electrorheological Effect

The suspended particles of an electrorheological (ER) fluid can be easily arrayed as a crystallite of a body-centered tetragonal (bct) lattice structure using an external electric field. Thus the entropy of this process, which is generally recognized as a first-order phase transition, would greatly decrease. From this fact, we theoretically derive that the dielectric loss tangent maximum value of the dispersed particles should be larger than 0.1, which agrees well with the currently observed experimental results; the negative ER effect becomes possible only when d∈ sp /dT < 0, where ∈ sp is the static dielectric constant of the dispersed particle material and T is temperature.

Urethane Modified Polyethers as Homogeneous Electrorheological Materials

Urethane modified polyethers having hard-soft-hard or soft-hard-soft structure were prepared by addition of isocyanate compounds and polyether glycols. It was found that a hard-soft-hard polymer prepared from polypropylene glycol and naphthalene diisocyanate shows an increase of viscosity in an electric field (positive electrorheological effect), while a soft-hard-soft polymer prepared with the same starting materials shows a decrease of viscosity (negative electrorheological effect). Viscosity measurements and NMR relaxation analyses of monodisperse model compounds were also performed to consider the mechanism of these opposite effects. Comparison of 'H-NMR relaxation times of modified and unmodified polyether indicated that the rapid mode of molecular motion is enhanced by the modification while the slow mode is restricted. The change of molecular movement by the modification of polyether is considered to play some role in the enhanced electro-responsive property.

Negative electrorheological effect and electrical properties of a Teflon/silicone oil suspension

A suspension (φ=0.2) of Teflon particles in silicone oil exhibited a negative electrorheological response with a dc electric field. This was in keeping with the fact that the conductivity of the host liquid σf was considerably greater than that of the particles σp, giving for the complex dielectric mismatch parameter β*=−1/2. Microscopy observations revealed that with application of a dc electric field the Teflon particles migrated to the positive electrode resulting in a structure which consisted of two layers or zones: (a) a relatively pure liquid and (b) a more concentrated suspension. The thickness of the liquid zone increased with field strength, which led to the decrease in the shear stress with field. A numerical analysis was developed for the electrical properties of the segregated suspension, which gave good agreement with measured values.

An anomalous electrorheological behavior of magnesium hydroxide suspensions in silicone oil

In contrast to the usual electrorheological behavior manifesting in an increase in viscosity of suspensions of various materials in electrical field, a negative electrorheological effect, i.e., a decrease in viscosity of suspensions of magnesium hydroxide particles in silicone oil was observed.