Electro-responsive Electrorheological Research Articles

Enhanced electro-responsive electrorheological efficiency of polyethylene oxide-intercalated montmorillonite nanocomposite suspension

Polyethylene oxide (PEO)-salt complex is an important polymer electrolyte-based anhydrous electrorheological (ER) material. However, it is difficult to get PEO-based ER material in particle form owing to the low glass transition temperature. Cross-linking and copolymerization with other polymers are widely used ways to form polyether-salt complex with desired dimensions and stability. However, these ways are relatively complex, and the ionic conductivity of resulting products is also too high for ER application. In this paper, we report a simple way to form PEO-based nanocomposite ER particles by intercalation chemistry with montmorillonite (PEO-MMT) under the help of ethanol solvent. The structure and composition of samples were characterized by X-ray diffraction, Fourier transform infrared spectroscopy, thermogravimetry, and so on. An increase in basal d001-spacings demonstrates successful intercalation of PEO in MMT. The electro-responsive ER effect of PEO-MMT suspension under electric fields was studied. It demonstrated that PEO intercalation not only effectively solved the problem of difficult granulation of PEO ER material but also replaced the absorbed water in the interlayer of MMT and greatly limited the ionic conductivity of MMT. Under electric fields, the suspension of PEO-MMT nanocomposite was found to show significant ER effect, weak current density, and wide working temperature range. A significant interfacial polarization process was observed by dielectric spectra measurement, which can explain the significant ER effect of PEO-MMT nanocomposite.

Electrorheology and dielectric polarization of backbone, pendant and cross-linked poly(ionic liquid)s

Backbone, pendant and cross-linked poly(ionic liquid) (PIL) particles with the same ion pair and similar ion number density have been prepared and the electro-responsive electrorheological (ER) effect of their suspensions in insulating carrier liquid has been comparably studied by rheology and dielectric spectroscopy. It has found that the ER effect of cross-linked PILs is strongest and that of backbone PILs is weakest. Dielectric spectrum analysis has showed that the difference of ER effect is mainly due to the difference in the ion leakage and effective interfacial polarization of PIL particles under electric fields. Although the backbone PILs have the largest interfacial polarization strength, its ion leakage conductance is also largest and this results in its weakest ER effect. The cross-linked PILs well restrains the ion leakage conductance and the ER effect is largely enhanced. The difference in ion leakage conductance and ER effect is further related to the difference of PIL matrix structure according to X-ray diffraction characterization. This study clarified the influence of matrix structure on ER effect and dielectric polarization of PILs and provided a guidance for the design of PIL ER materials.

Understanding the enhanced electrorheological effect of reduced graphene oxide‐supported polyaniline dielectric nanoplates by a comparative study with graphene oxide as the support core

Graphene has attracted scientific interest as a substrate or additive for developing high-performance stimuli-responsive materials. Research on graphene-based polymer dielectric composites has shown an enhanced electroresponsive electrorheological (ER) effect. However, the mechanism behind the enhanced electroresponse is still incompletely understood. Here, an investigation was performed into dielectric polarization and the ER effect of reduced graphene oxide-supported polyaniline nanoplates by comparing them with pure granular polyaniline and graphene oxide-supported polyaniline nanoplates based on dielectric spectroscopy and rheologic analysis. We discovered that both anisotropic morphology and electrical properties have dominant roles in the enhanced ER effect of reduced graphene oxide-supported polyaniline nanoplates, whereas only anisotropic morphology has a dominant role in the enhanced ER effect of graphene oxide-supported polyaniline nanoplates. The analysis also showed that reduced graphene oxide-supported polyaniline nanoplates have a good ER response to both DC and AC electric field actions in the wide shear rate region. This is highly desirable for practical engineering applications. Therefore, the analysis reveals the reason for the enhanced ER effect of reduced graphene oxide-supported polyaniline nanoplates and also may provide a guide for designing high-performance ER materials for practical engineering applications by combining the advantages of conducting a reduced graphene oxide core and ER active shell.

Interfacial Polarization and Electroresponsive Electrorheological Effect of Anionic and Cationic Poly(ionic liquids)

Owing to weak ion pair electrostatic interaction and intrinsically hydrophobic nature, poly(ionic liquids) (PILs) have potentiality as anhydrous polyelectrolyte-based electrorheological (ER) smart ...

Ion transport, polarization and electro-responsive elelctrorheological effect of self-crosslinked poly(ionic liquid)s with different counterions

Self-crosslinked bis(imidazolium)-based poly(ionic liquid)s (PILs) containing different counterions (P[C2DVIM][X], X = BF4−, PF6−, TfO−, TFSI−) are synthesized and the influence of counterions on electro-responsive electrorheological (ER) effect is studied in order to understand the structure-property relationship of crosslinked PIL-based ER system. It is found that the size and type of counterions have a significant influence on ER effect. As the size increases, the ER effect decreases (i.e. BF4− > PF6− > TfO− > TFSI−). Different from the linear PIL-based ER system, however, the P[C2DVIM]X with inorganic counterions shows stronger ER effect compared to P[C2DVIM]X with organic counterions. Meanwhile, the influence of counterions on temperature dependence of ER effect of the crosslinked PIL system is also different from the linear PIL system. By dielectric spectroscopy and X-ray scattering measurements, the mechanism behind the influence is analyzed. It demonstrates that, different from linear PIL system, the ionic aggregation is largely weakened in P[C2DVIM]X and the transport of mobile counterions and interfacial polarization are mainly dominated by the mesh size of crosslinking network. This should be responsible for the different dependence of ER effect on the size and type of counterions between self-crosslinked and linear PIL systems.

Enhancing Electroresponsive Electrorheological Effect and Temperature Dependence of Poly(ionic liquid) Particles by Hard Core Confinement.

Monodisperse core-shell-structured SiO2@poly(ionic liquid) (SiO2@PIL) particles are prepared by the polymerization of ionic liquid monomer on the surface of methacryloxypropyltrimethoxysilane-modified SiO2 particles. The electroresponsive electrorheological (ER) effect of SiO2@PIL particles when dispersed in insulating carrier liquid is investigated and compared with that of pure poly(ionic liquid) (PIL) particles based on temperature-modulated rheology under electric fields. It is demonstrated that hard SiO2 core not only enhances the ER effect of PIL particles but also improves the temperature dependence of ER effect. By dielectric spectroscopy analysis, the mechanism behind the property enhancement was discussed. It indicates that the hard SiO2 core can not only increase the interfacial polarization strength of SiO2@PIL particles by core-shell architecture but also restrain the segment relaxation or softening of the PIL shell and influence the ion dynamics above the calorimetric glass transition of PILs by the so called "substrate confinement effect", and this should be responsible for the enhanced electroresponsive ER effect and temperature stability of the SiO2@PIL particles.

Distinctly Different Electroresponsive Electrorheological Effect in Low-Molecular-Weight and Polymerized Ionic Liquids: Rheological and Dielectric Relaxation Studies.

Owing to the robust and tunable properties compared to molecular compounds, ionic liquids (ILs) and polymeric ionic liquids (PILs) are very suitable substances to obtain available smart materials with high stability and strong stimulus-responsive characteristic. In this paper, electroresponsive smart electrorheological (ER) effects in low-molecular-weight and polymeric ionic liquids, such as poly[[2-(methacryloyloxy)ethyl]trimethylammonium hexafluorophosphate] (P[MTMA][PF6]) are investigated and compared by a combination of rheology and dielectric relaxation spectroscopy. It is found that although P[MTMA][PF6] and [MTMA][PF6] have same constituent ions, their ER effect is distinctly different. Under electric fields, the ER effect of P[MTMA][PF6] exceeds that of the low-molecular-weight monomeric counterpart by 2-fold of magnitude. As the temperature increases, the ER effect of P[MTMA][PF6] remains in a stable level in wide temperature region, whereas that of [MTMA][PF6] shows strong temperature dependence. By dielectric relaxation spectroscopy, it can clarify that the different ER effect is attributed to the different polarization characteristics induced by cation/anion pair in different substance circumstances. Compared to low-molecular-weight crystal [MTMA][PF6], the slow interfacial polarization with a good temperature dependency related to strong ER effect in wide temperature region is easier to occur in P[MTMA][PF6] because its amorphous polymeric matrix circumstance not only provides lower activation energy for the dissociation and diffusion of ions, but also limits the dissolution of ions in carrier liquid. The result not only deepens the understanding about mechanism behind the electroresponsive ER effects of ILs and PILs but also highlights the potential of PILs as high-performance stimuli-responsive ER materials compared to the low-molecular-weight monomeric counterpart.

Fabrication and electro-responsive electrorheological characteristics of rice husk-based nanosilica suspension

Abstract Rice husk-based nano-sized silica particles were prepared using both acid and thermal treatment methods for applications to electro-responsive electrorheological (ER) fluids when dispersed in silicone oil. The morphology of the nano-sized silica particles was observed by scanning electron microscopy, and their chemical structure and thermal stability were examined by Fourier-transform infrared spectroscope and thermo-gravimetric analysis, respectively. The ER properties of the nano-sized silica particle-based ER suspension was investigated using a rotation rheometer under various electric field strengths, showing a conduction mechanism with a slope of 1.5 for a plot of the yield stress versus the applied electric field strength. In addition, its shear stresses increased with increased electric field strengths along with ER efficiency and became stable over the entire shear rate range when the electric field reached 2.0 kV/mm. Typical solid-like behaviors of the ER suspension was also confirmed by both higher storage moduli than the loss moduli and shear relaxation modulus property.

Low-Temperature Interfacial Polymerization and Enhanced Electro-Responsive Characteristic of Poly(ionic liquid)s@polyaniline Core-shell Microspheres.

The synthesis of monodisperse poly(ionic liquid)s (PILs) microspheres coated with semiconducting polyaniline (PANI) shell is reported, which shows enhanced electro-responsive electrorheological (ER) effect but decreased power consumption compared to neat PIL microspheres. The monodisperse PIL microspheres are first prepared via dispersion polymerization and then PANI is coated via low-temperature interfacial polymerization of aniline on the surface of hydrophobic PIL microspheres without additional modification. The stimulus-responsive ER effect of the core-shell microspheres when dispersing in insulating oil are investigated under electric fields. The power-law of yield stress versus electric field strength and the dielectric relaxation spectroscopy are analyzed to understand the ER effect and the origin of property enhancement. It demonstrates that the semiconducting PANI shell can well limit the irreversible ion leakage of PIL microspheres and improve the particle polarizability, resulting in decreased power consumption but enhanced electro-responsive ER effect.

Cellulose-Based Smart Fluids under Applied Electric Fields.

Cellulose particles, their derivatives and composites have special environmentally benign features and are abundant in nature with their various applications. This review paper introduces the essential properties of several types of cellulose and their derivatives obtained from various source materials, and their use in electro-responsive electrorheological (ER) suspensions, which are smart fluid systems that are actively responsive under applied electric fields, while, at zero electric field, ER fluids retain a liquid-like state. Given the actively controllable characteristics of cellulose-based smart ER fluids under an applied electric field regarding their rheological and dielectric properties, they can potentially be applied for various industrial devices including dampers and haptic devices.

Synthesis of semiconducting poly(diphenylamine) particles and analysis of their electrorheological properties

Poly(diphenylamine) (PDPA) particles were synthesized as a novel semiconducting electro-responsive electrorheological (ER) material by a chemical oxidative polymerization process and their ER characteristics were investigated at various electric fields. Surface morphology of these N-aryl-substituted polyaniline-derived PDPA particles was examined by scanning electron microscopy and their chemical structure and thermal properties were confirmed by Fourier-transform infrared spectroscopy and thermogravimetric analysis, respectively. Their susceptibility to electric fields and the chain formation of dispersed particles were observed directly using optical microscopy. Rheological analysis of the PDPA-based ER fluid was performed using a combination of steady shear and oscillation tests in a Couette-type rotational rheometer with a high-voltage power supply. The measurements were performed in controlled shear stress and shear rate modes under the varied electric field strengths. The Cho–Choi–Jhon model was found to determine the stress behavior more clearly. Dielectric analysis provided additional information about the electrical polarization properties and thus also the ER performance of the PDPA-based ER fluid.

Swelling-diffusion-interfacial polymerized core-shell typed polystyrene/poly(3, 4-ethylenedioxythiophene) microspheres and their electro-responsive characteristics

We synthesized core-shell structured conducting polystyrene/poly(3,4-ethylenedioxythiophene) (PS/PEDOT) microspheres and examined their electro-responsive electrorheological (ER) properties under an applied electric field when dispersed in a silicone oil. Monodisperse PS particles 1.05 μm in diameter were initially fabricated via dispersion polymerization, and PS/PEDOT microspheres with average diameters of approximately 1.07 μm were prepared by a swelling-diffusion-interfacial polymerization process. The morphology of the PS/PEDOT microspheres was confirmed by both field emission scanning electron microscopy and transmission electron microscopy, while their chemical structure was characterized by Fourier transform infrared spectroscopy. Formation of particle chains in the ER fluid was directly observed by optical microscopy under an applied electric field. The rheological behavior of the PS/PEDOT particle-based ER fluid was examined using a rotational rheometer on particles dispersed in silicone oil at a volume fraction of 10%. As the electric field was strengthened, the performance of the ER fluid was also enhanced. The dielectric spectra were also well correlated to their ER effects using an LCR meter.

Highly stable nanofluid based on polyhedral oligomeric silsesquioxane-decorated graphene oxide nanosheets and its enhanced electro-responsive behavior

Graphene oxide (GO) shows potential as an anisotropic nanofiller or a dispersed phase of electro-responsive electrorheological (ER) nanofluid due to its small size and high aspect ratio. But it is difficult to disperse GO in non-polar oil due to the hydrophilic nature of GO and thus the resulting fluid is often subject to dispersion instability and low ER effect. These disadvantages largely limit the real application of GO-based ER nanofluid. In this paper, we develop the polyhedral oligomeric silsesquioxane (POSS)-decorated GO (POSS-GO) nanosheets and demonstrate that decorating with POSS overcomes the dispersion instability of GO in silicone oil and enhances the ER effect. The morphology and structure of samples are characterized by atomic force microscopy, Fourier transform infrared spectroscopy, thermogravimetric analysis, and x-ray photoelectronic spectroscopy. The results show that the POSS-GO nanosheets are ultrathin with ∼3 nm thickness and have good compatibility with silicone oil and, as a result, the nanofluid of POSS-GO nanosheets in silicone oil shows high dispersion stability. After standing for one year at room temperature, no sedimentation occurs. Under an external electric field, the ER efficiency of the POSS-GO nanofluid is ten times as high as that of the pure GO fluid. This enhanced electro-responsive behavior is related to the fact that decorating with POSS partly reduces the GO and compresses the dielectrophoretic effect of the negatively charged pure GO fluid.

Stimuli-Responsive Polymer-Clay Nanocomposites under Electric Fields.

This short Feature Article reviews electric stimuli-responsive polymer/clay nanocomposites with respect to their fabrication, physical characteristics and electrorheological (ER) behaviors under applied electric fields when dispersed in oil. Their structural characteristics, morphological features and thermal degradation behavior were examined by X-ray diffraction pattern, scanning electron microscopy and transmission electron microscopy, and thermogravimetric analysis, respectively. Particular focus is given to the electro-responsive ER characteristics of the polymer/clay nanocomposites in terms of the yield stress and viscoelastic properties along with their applications.

Fabrication and stimuli response of rice husk-based microcrystalline cellulose particle suspension under electric fields

We report on the electro-responsive electrorheological (ER) properties of microcrystalline cellulose (MCC) particles. It was synthesized from raw rice husk (Downes Rice) through the 3-step preparation of alkali treatment, bleaching, and hydrolysis. The MCC particles with mean particle size about 26 μm were characterized by scanning electron microscopy, Fourier transform infrared spectroscopy and thermal gravimetric analysis. The MCC particles were then dispersed in silicone oil to create an ER fluid; its dramatic electro-responsive phase changes under an applied electric field were observed by an optical microscopy. The effect of electric field strengths on ER performances of the ER fluid were determined using a rotational rheometer equipped with a high-voltage generator from the controlled shear rate mode and dynamic oscillation measurements. The fluid showed typical ER effects of Bingham fluid behavior with yield stress and viscoelastic properties under an applied electric field.

Silicone-grafted carbonaceous nanotubes with enhanced dispersion stability and electrorheological efficiency

Carbonaceous particles are types of important fillers or dispersed phases of electro-responsive electrorheological (ER) suspensions. But carbonaceous particles, in particular with nano-order size, are easy to aggregate in oils. This characteristic limits the application of ER suspensions based on carbonaceous particles. In order to improve dispersion stability and ER efficiency, in this paper, we develop silicone-grafted carbonaceous nanotubes (CTs) by grafting oxidized carbonaceous nanotubes with epoxy-terminated silicone. The samples are characterized by Fourier transform infrared spectra, x-ray photoelectron spectroscopy, thermogravimetric analysis, and transmission electron microscopy. The wettability and dispersion stability of nanotubes in silicone oil are investigated by wetting curves and sedimentation tests. The ER properties of CTs when dispersed in silicone oil are measured by a rheometer under electric fields. It demonstrates that grafting with silicone can distinctly improve the wettability of CTs in silicone oil and decrease the re-aggregation of CTs. As a result, the suspension of silicone-grafted CTs in silicone oil shows high dispersion stability. Compared to the suspension of bare CTs, the suspension of silicone-grafted CTs exhibits lower zero-field viscosity but higher field-induced viscosity; thus it possesses higher ER efficiency. This enhanced ER efficiency is related to the improved wettability of silicone-grafted CTs in silicone oil.

Graphene and Graphene Oxide Composites and Their Electrorheological Applications

Graphene oxide (GO) based composite systems have been fabricated and investigated as a novel electroresponsive electrorheological (ER) dispersed phase because of their proper electrical conductivity and polarizability for their ER application, in addition to graphene composites. This paper briefly reviews mechanisms of the fabrication of various graphene and GO based composites and their critical ER characteristics including flow curve, yield stress, and dynamic properties measured using a rotational rheometer. Relaxation time and achievable polarizability from dielectric analysis using a LCR meter are also discussed.

Monodisperse poly(2-methylaniline) coated polystyrene core–shell microspheres fabricated by controlled releasing process and their electrorheological stimuli-response under electric fields

A core–shell structured electro-responsive electrorheological (ER) particle system comprised of monodisperse poly(2-methylaniline)-coated polystyrene (PS/PMAN) microspheres was fabricated by applying a controlled swelling-releasing technique to pre-fabricated micron-sized PS seeds using a dispersion polymerization method. Compact wrapping of the PS microparticles with semiconducting PMAN without a de-doping process was examined by scanning electron microscopy and transmission electron microscopy. Fourier-transform infrared spectroscopy and thermogravimetric analysis also confirmed the chemical composition and thermal stability of the particles, respectively. Rheological characteristics of the PS/PMAN microsphere based ER fluid dispersed in silicone oil at various electric field strengths revealed a typical ER response under both steady shear flow and dynamic oscillation, demonstrating its mechanism of a conductivity model with a slope of 1.5.

Enhanced dielectric polarization and electro-responsive characteristic of graphene oxide-wrapped titania microspheres

Electric field-induced particle polarization is essential to the electro-responsive electrorheological (ER) effect of particle suspensions. In this work, we use graphene oxide (GO) as a soft and polar coating shell to prepare GO-wrapped titania dielectric microspheres for use as the dispersal phase of an ER suspension. Under a DC electric field, the ER characteristic of GO-wrapped titania microspheres dispersed in silicone oil is investigated by rheological tests, and then compared with that of a suspension of bare titania microspheres. The results show that the suspension of GO-wrapped titania microspheres possesses an enhanced ER characteristic. Its field-induced shear yield stress and storage modulus are much higher than those of the suspension of bare titania microspheres. The soft and polar GO shell is regarded as the origin of the ER enhancement. Dielectric analysis indicates that wrapping GO can enhance the interfacial polarization and thus improve the ER characteristics of titania microspheres. Wrapping GO onto the surface of titania microspheres can also reduce the particle sedimentation velocity of the suspension.

Urchin-like polyaniline microspheres fabricated from self-assembly of polyaniline nanowires and their electro-responsive characteristics

Micron-sized PANI beads with a porous sea urchin like appearance, mean diameter of 2.5μm and spherical shape, were synthesized by a self-assembly process from PANI nanowires. The nanowires were polymerized using ammonium persulfate as an oxidant in an aqueous solution. The structure of the urchin-like PANI microspheres was characterized by scanning electron microscopy, while the Brunauer–Emmett–Teller specific surface area of the urchin-like PANI microspheres was calculated from N2 adsorption/desorption. The microspheres, which were dedoped to a low conductivity, were then applied to electro-responsive electrorheological (ER) materials dispersed in silicone oil with a volume fraction of 10%. The particulate structures of the ER fluid under an applied electric field were observed by optical microscopy. The ER properties of the ER fluid including the shear stress, shear viscosity and yield stress were examined using a rotational rheometer under an applied electric field.