Electrorheological Response Research Articles

Core/shell-structured, covalently bonded TiO2/poly(3,4-ethylenedioxythiophene) dispersions and their electrorheological response: the effect of anisotropy

Higher surface area, rod-to-rod interactions and conducting thin shell induced covalently-bonded core/shell nanorod-TiO2/PEDOT nanocomposite to show stronger ER activity and higher recovery after stress loading compared to particulate one.

A polymer/clay nanocomposite gel via chlorinated paraffin solvent initiated photopolymerization with electrorheological performance

This communication reports a mild preparation of a polymer/clay nanocomposite gel of chlorinated paraffin with an electrorheological response to an external direct-current voltage due to the alignment of the clay within the gel networks.

Electro-active elastomer composites based on doped titanium dioxide

The TiO2-Acac/PDMS elastomer conserves a high elastic modulus change (ΔG′) after cross-linking and achieves ΔG′ higher than 500 kPa for an applied electric field of 2 kV mm−1.

Electrorheological response measured with pectinated electrodes

Pectinated electrode has been designed to measure the rheological property of electrorheological (ER) fluids. The principle of this measurement is based on the effect that the outside electric field near the edges of parallel electrode can contribute a considerable value of the field. The relations of the yield stress and the gap between pectinated electrode and workpiece, as well as the variations of the yield stress versus the parameters of pectinated electrodes have been obtained. It is found that the yield stress can be much enhanced when the gap is small and decreases with the gap increasing. The mechanism of those phenomena is explained. This knowledge of the ER behavior by using pectinated electrode must be helpful for the design of device in the applications of ER fluid.

Silica prepared in the presence of alkylphosphonium-based ionic liquids and its performance in electrorheological fluids

This work highlights the effect of silica particles prepared by a sol–gel process in the presence of different phosphonium-based ionic liquids on the electrorheological behavior of the corresponding suspension in silicone oil. The silica particles were prepared by hydrolysis/condensation of tetraetoxy silane (TEOS) in basic medium and in the presence of three different commercial ionic liquids: tri-isobutyl(methyl)phosphoniumtosylate (IL106), tri(n-butyl)(tetradecyl)phosphonium-dodecylbenzene-sulfonate (IL201) and trihexyl-(tetradecyl)-phosphonium-bis-2,4,4-(trimethylpentyl)-phosphinate (IL104). The resulting material was characterized by Fourier-transform infrared spectroscopy (FT-IR), thermo-gravimetric analysis (TGA), scanning electron microscopy (SEM) and dielectric properties. The confinement of the ionic liquids inside the silica particles was suggested by thermogravimetric analysis. The presence of ILs also exerts a strong influence on the morphology and imparts good polarization ability to the silica. The electro-rheological response of the corresponding ionogel suspensions in silicone oil was investigated. A significant ER effect was observed for the fluid containing silica prepared in the presence of IL106. In fact, a very good response under the action of an electrical field corresponding to 3 kV mm−1 was achieved, with a shear stress value as high as 1215 Pa. This behavior may be attributed to the presence of the IL confined in the silica particles and also to the peculiar morphology which favors the formation of a columnar structure to a high extent.

Physicochemical and electrorheological properties of titanium dioxide modified with metal oxides

The properties of electrorheological fluids containing dispersed phase of titanium dioxide nanoparticles prepared via the sol-gel method and modified with metal oxides have been studied. Titanium dioxide has the anatase structure with crystallite sizes of 8–10 nm and a specific surface area of 90–140 m2/g. It has been found that the magnitude of the electrorheological response of the filler is determined by the specific surface area and the content of a modifying component. The strongest electrorheological response has been revealed for titanium dioxide modified with aluminum oxide at an Al content of 6.5–7.0 mol % relative to TiO2.

Enhanced effect of dopant on polyaniline nanofiber based electrorheological response

As a potential candidate for electrorheological (ER) materials, polyaniline (PANI) nanofibers were synthesized via an interfacial polymerization route, because of their easy synthesis, high stability, controllable conductivity and good ER response. In this study, a new dopant, indole-2-carboxylic acid, was used to improve the ER performance. The synthesized PANI nanofibers were dispersed in silicone oil at 10 vol% and their rheological properties as an ER fluid were examined using a rotational rheometer under a variety of electric field strengths. In addition, their dielectric properties were studied using a LCR meter. The results showed that indole-2-carboxylic acid, which has high polarizability, enhanced the ER effect of PANI nanofibers, showing that polarizability is an important parameter affecting the ER behavior.

Electric-field-induced structure and optical properties of electrorheological fluids with attapulgite nanorods

Attapulgite (ATP) is a type of crystalloid hydrous magnesium-aluminum silicate mineral with natural one-dimensional (1D) fibrous morphology. In this study, the authors investigated the optical and mechanical performances of ATP nanorods in silicone oil under an electric field. It was observed that the optical transmittance of ATP suspensions decreased rapidly under the low electric field, using ultraviolet-visible (UV-Vis) spectroscopy. The results of optical microscopy and scanning electron microscopy (SEM) indicated that the electromigration of ATP nanorods was the major cause of such an aberrant optical phenomenon. Further, the electrorheological (ER) response of the samples was measured by the height-controlled method. The change trend of the normal force was illustrated by the dynamic assembly behavior of ATP in the applied electric field. This work provided intuitive evidence for an in-depth understanding of the mechanism of ER fluids containing 1D dielectric materials.

Electrorheological response of the interfacial layer between a liquid crystal and a polymer alignment sublayer

The interfacial layer between a liquid crystal (LC) and a polymer alignment sublayer was investigated using the quartz crystal microbalance (QCM) method. The time variations in the optical transmittance through the LC cells and the interfacial viscoelasticity were monitored simultaneously using the QCM to provide a comprehensive picture of the interfacial phenomena associated with the motion of LC molecules both in the bulk and in the interfacial layer. The response time of shift in the resonant resistance associated with the director orientation in the interfacial layer was about 90ms, while that in the LC bulk was about 5ms. This indicates that the reorientation of the LC molecules in the vicinity of the interface is much slower than in the bulk. The response time for the changes in thickness of the adsorbed layer, as estimated from the QCM results, was found to be about 1000ms. These results indicate that the electrorheological response, or the viscoelasticity, in the vicinity of the interface between the LC and the polymer should be taken into account for the development of LC devices.

Core–Shell-Structured Monodisperse Copolymer/Silica Particle Suspension and Its Electrorheological Response

Monodisperse core-shell-structured poly(styrene-co-butyl acrylate-co-[2-(methacryloxy)ethyl] trimethylammonium chloride)/silica (PSBM/SiO2) nanoparticles were applied as new electrorheological (ER) materials in which the particles were dispersed in an insulating oil. These nanoparticles were prepared by the consecutive precipitation of cetyltrimethylammonium bromide and negatively charged tetraethylorthosilicate onto the cationic surfaces of PSBM colloidal particles. The successful deposition of the shell phase of the particles and their morphology was examined by transmission and scanning electron microscopy. Their ER properties were studied with a rotational rheometer under different shear modes: controlled shear rate, steady shear under constant shear rate, and creep test. The silica shell allowed the PSBM/SiO2 particles to exhibit typical ER performance under an applied electric field. The dielectric spectra of the PSBM/SiO2-based ER fluid were also recorded using an LCR meter, which was correlated to the ER performance of the ER fluid.

Electrorheological response of inorganic-coated multi-wall carbon nanotubes with core–shell nanostructure

The effect of coating thickness and sequence on the multi-wall carbon nanotube (MWCNT) surface on electrorheological (ER) activity is investigated. Silica-coated MWCNTs with different shell thicknesses and inorganic-coated MWCNTs with different shell sequences are fabricated using the sol-gel process. The morphology and elemental analyses of the core-shell structured MWCNTs were performed and the effect of coating thickness and coating materials on the MWCNT surface on ER and dielectric properties of inorganic-coated MWCNT suspensions have been analyzed from the measurement results of shear stress, viscosity, current density and permeability. The electrical conductivity of silica-coated MWCNTs decreases with an increase of the shell thickness. However, the dynamic yield stress and viscoelastic properties under an external electric field increased when the shell thickness reached 20 nm and then decreased with the thickness up to 40 nm. However, the titania-coated MWCNT suspension with a shell thickness of 40 nm showed the highest dynamic yield stress compared to the other core-shell structured MWCNT suspension at the same volume fraction. It has been found that the material of the outermost shell plays an important role in the ER performance. It has been concluded that the electrical conductivity and the permittivity of the MWCNTs can be controlled by adjusting the coating thickness and sequence of inorganic materials.

Hybrid polyaniline-coated sepiolite nanofibers for electrorheological fluid applications

Hybrid materials constituted by sepiolite covered with polyaniline (PAni) with different compositions have been prepared using two simple methods: bulk and slurry oxidative polymerization. The hybrid nanofibers were characterized by Fourier transform-infrared (FTIR) spectroscopy, transmission electron microscopy (TEM), thermo-gravimetric analysis (TGA), electrical conductivity, dielectric spectroscopy analysis and electrorheological response. Fiber-based nanocomposites with PAni nanoparticles well adhered to the sepiolite surface were successfully prepared by slurry polymerization. The best recovering of the nanofibers was observed in nanocomposites containing 46wt% of PAni, (SP 50:50s sample) as indicated by FTIR and TEM and quantified by TGA analysis. Also the best electrorheological response was obtained with the corresponding suspensions containing 10wt% of the hybrid material suspended in castor oil. The values of the field induced shear modulus in the linear viscoelastic region: G′=536kPa at E=2kV/mm is higher than those found for the suspensions of pure components, PAni or sepiolite, and one of the best values obtained with conventional ER fluids. A model to estimate the interaction between two nanofibers has been proposed considering the length and thickness of the nanofiber, calculated by TEM.

Double template assisting synthesized core–shell structured titania/polyaniline nanocomposite and its smart electrorheological response

Abstract Monodispersed titanium oxide nanospheres were synthesized via the controlled hydrolysis method in this study firstly. Then the rapid mixing method was used to in situ oxidation polymerize aniline, which can modify the surface of titanium oxide nanospheres to form a core/shell nanostructure. Scanning electron microscopy (SEM), transmission electron microscopy (TEM), X-ray diffraction (XRD) and rotational viscometer were used to investigate its structure, morphology and properties. The different type and dosage of surfactants, different acids, crystal forms of titanium oxide and different dosages of aniline were studied to analysis the impact on the TiO2/PANI nanocomposites. The suitable type and dosage of surfactants, the ratio of aniline to titania were the key to synthesize the nanocomposite, which can include nanoring, nanofiber or nanoparticles core/shell composite depending the synthesis condition. The titania/polyaniline composite showed typical electrorheological (ER) behavior, which demonstrated its potential applications as an ER smart material.

Characterization and electrorheological response of silica/titania-coated MWNTs synthesized by sol–gel process

Silica or titania uniformly coated multi-walled carbon nanotubes (MWNTs) were fabricated using the tetraethyl orthosilicate (TEOS) or titanium butoxide (TBT) for the application of electrorheological (ER) fluids. The electrorheological and dielectric properties of the two different core/shell nano-tube based ER fluids were measured using rheometer and impedance analyzer. The titania-coated MWNTs ER fluids have shown higher static yield stress as well as dynamic viscoelastic properties compared to the silica-coated MWNTs ER fluids under external electric field. The silica or titania-coated MWNTs ER fluids have shown high permittivity and short relaxation time of interfacial polarization in the dielectric spectra measurement. It was found that the permittivity and electrical conductivity of the MWNTs can be controlled by coating with either the silica or titania onto the functionalized MWNTs.

Negative electrorheological responses of mono-dispersed polypyrrole-SAN copolymer suspensions

The mono-dispersed polypyrrole (PPy)-poly(acrylonitrile-co-styrene) (SAN) copolymer particles were synthesized by emulsion polymerization and the electrorheological (ER) behavior of their suspensions was investigated. The suspensions of the mono-dispersed PPy-SAN copolymer particles showed negative ER effects. It was quite unexpected to negative ER effects for ER suspensions of conducting polymers or conducting polymer composites. The ER responses decreased with increasing electric field strength and particle size. A power-law dependence on the particle size and the electric field strength, τ(E)-τ0=−103.95 d−2E, showed a reasonable fit to the dynamic yield stress differences. It was observed that particles separated between the electrodes during experiments under the applied electric field. The migrations due to charge injection, by which the gap between the electrodes devoid of particles, seem to play a role in the yield stress decrease, leading to the negative ER response. Open image in new window

Electric-field-induced structuring and rheological properties of kaolinite and halloysite

Electric-field-induced structuring of kaolinite and halloysite particles was studied in respect to their electrorheological (ER) response in silicone oil and in paraffin dispersions. The structural and morphological properties of both clay minerals were studied by XRD, FTIR, SEM, TEM and TGA techniques. The dipolar arrangement induced under application of an electric field was investigated by 2D-WAXS and optical microscopy techniques. The ER response of the samples was measured by both the shear rate controlled method and bifurcation tests. Kaolinite particle dispersions were found to have an improved ER response relative to dispersions of halloysite particles. Finally, the electric currents of these ER fluids were measured and the results revealed differences in the current-magnitude between halloysite- and kaolinite-based silicone oil dispersions.

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.

Modified titania and titanium-containing composites as fillers exhibiting an electrorheological effect

SiO2/TiO2 nanocomposites and individual titania (S = 30–500 m2/g) have been prepared through cohydrolysis of organomineral silicon and titanium derivatives in the presence of templates. We demonstrate that heterovalent substitution of chromium or cerium for titanium increases the thermal stability of TiO2 in terms of its crystallite size and specific surface area. After drying at 120°C, fillers based on SiO2/TiO2 composites (coprecipitated and core-shell SiO2/TiO2 particles) exhibit a significant electrorheological response due to appreciable hydrate and hydroxyl layers on the surface of the particles. Structural modification of titania also allows one to increase the electrorheological effect through an increase in specific surface and defect formation.

Electrorheological response of polyaniline and its hybrids

AbstractOne of the remarkable applications of conducting polymers is as an electrorheological (ER) fluid which is a smart suspension of polarisable particles dispersed in an insulating liquid with the capacity to effect a phase transition from a liquid-like to a solid-like state. Polyaniline (PANI) and its hybrids with inorganics or other polymers are active candidates for ER materials due to their various advantages, e.g., easy synthesis, controllable conductivity, and less friction than pure inorganics. In this short review, we review recent progress in the synthesis of semi-conducting PANI and its hybrids with diverse morphologies and their ER performance measured by a rotational rheometer using the applied electric field strength. The dielectric properties of these ER fluids, as an important analytical method for their ER performance, are also discussed.