Electrorheological Effect Research Articles

Electrorheological Effect in a Dual-frequency Nematic Liquid Crystal: A Theoretical Study Based on the Ericksen–Leslie Theory

We have theoretically investigated the electrorheological effect in a dual-frequency liquid crystal, in which the dielectric anisotropy depends on the frequency of an applied ac electric field. In ...

Experimental investigations on electrorheological properties of lubricating oils containing ionic liquid. Part 2. Testing in dielectric spectroscopy

The paper presents the results of investigations of two mixtures and their ingredients i.e. base insulating oils and ionic liquids as electrically active additives using, so called, dielectric spectroscopy. In part 1 of the study [1], the ER effect was found in both mixtures when they were subjected to an external constant electric field with the intensity of E ≤ 0.2 kV·mm–1. However, the electrorheological effect was short-lived and unique on the same liquid sample, which suggested significant changes in its internal structure. Using the HP 4192 A Hewlett Packard impedance analyzer, the variability of their dielectric constans (), as well as the resistance (R) and the conductivity (σ), as a function of the frequency (f) of the constant electric field BIAS-u (DC) was assessed for different values of the applied voltage (U). Repeated tests were also carried out on the same samples of mixtures to observe how the originally applied BIAS field affects the further behavior of the liquid in the electric field. Based on the results of the research, the basis for confirming the symptoms of changes in the internal structure of mixtures, resulting, from the action of an external electric field, leading to the disappearance of the ER effect was obtained. In order to recognize the mechanism of disappearance of the ER effect, in situ microscopic tests of the prepared mixtures, subjected to an external electric field, will be carried out. Keywords: electrorheological effect, lubricating oils, ionic liquids, dielectric spectroscopy

On the enhanced sedimentation stability and electrorheological performance of intelligent fluids based on sepiolite particles

Electrorheological fluids are intelligent materials with the potential for use in a breadth of applications. However, their utilization has been restricted due to poor sedimentation stability and limited performance in the presence of an electric field. Our study investigates the possibility of employing sepiolite particles with their thickness in nanometres to enhance the sedimentation stability of electrorheological fluids. Indeed, the high aspect ratios of such particles have the potential to heighten any electrorheological effect. The rheological properties of the fluids were gauged via steady shear and oscillatory shear tests, in the absence or presence of an external electric field. The electrorheological performance of the systems was further analysed with the aid of dielectric spectroscopy. A test sample containing the greatest amount of sepiolite particles (15 wt%) in a silicone-oil based system was observed to create a solid gel-like structure that completely suppressed sedimentation of the particles; thus, its sedimentation ratio after 200 h was equal to 1. Viscoelastic moduli obtained during measurements for amplitude sweep in the absence of an electric field confirmed a certain extent of elastic behaviour, while the resultant structure exhibited a relatively solid characteristic.

Electrorheological properties of polyimide nanoparticles suspensions

Suspensions of polyimide particles were obtained, in which 2,5-diaminobenzenesulfonic acid was used as a diamine component. Their electrorheological properties in a nonconducting medium were studied depending on the parameters of deformation and the intensity of the external electric field. It is established that the electro-rheological suspensions obtained based on particles of polyimide PI-I–PI-IV have a powerful electro-rheological response, ten times higher than the electro-rheological effect of suspensions based on traditional micro-sized particles of the dispersed phase.

Nonmonotonic Influence of Size of Quaternary Ammonium Countercations on Micromorphology, Polarization, and Electroresponse of Anionic Poly(ionic liquid)s.

The size influence of quaternary ammonium countercations in poly[4-styrenesulfonyl(trifluoromethylsulfonyl)imide][tetraalkylammonium] (P[STFSI][Nnnnn], n = 1, 2, and 3) poly(ionic liquid)s on dielectric polarization and the stimuli-responsive electrorheological effect is investigated by dielectric spectroscopy and rheology, and the microstructure-level understanding behind the influence is analyzed by Raman and X-ray scattering spectra. The size influence of quaternary ammonium cations is found to be nonmonotonic. The largest electrorheological effect accompanied by best polarization properties is demonstrated in P[STFSI][N2222]. Raman spectra and activation energy measurements demonstrate that the nonmonotonic influence originates from the fact that, compared to small N1111+ and large N3333+, intermediate N2222+ as countercations can contribute a higher mobile ion number and lower activation energy barrier of ion dissociation and motion. But the experimental values of activation energy are not consistent with theoretically calculated values by considering the ion pair electrostatic potential and elastic force contribution of the matrix. By X-ray scattering and diffraction characterizations, it is clarified that the nonmonotonic influence and the inconsistency of activation energy originate from the size influence of Nnnnn+ on the micromorphology of P[STFSI][Nnnnn]. Compared to the semicrystalline structure of P[STFSI][N1111] and the ionic aggregation structure of P[STFSI][N3333], the relatively uniform amorphous structure of P[STFSI][N2222] may be responsible for its lower activation energy barrier of ion motion. This study further provides insights into the design and preparation of future poly(ionic liquid)-based electrorheological materials by considering not only molecular structure but also micromorphology.

Synthesis of hollow TiO2 nanobox with enhanced electrorheological activity

TiO2 nanoboxes with a hollow interior space, derived from titanium oxydifluoride (TiOF2) nanocubes, were prepared using a two-step method, in which the TiOF2 nanocubes acting as the precursor were first synthesized using a typical hydrothermal route. Subsequently, a second hydrothermal step was developed to prepare the TiO2 nanoboxes. The clear phase transformation from the TiOF2 precursor to anatase TiO2 was confirmed using X-ray diffraction, Fourier-transform infrared spectroscopy, and X-ray photo-electron spectroscopy analyses. The evolution of the morphology from a nanocube to nanobox was revealed by scanning electron microscopy and transmission electron microscopy observations. The influences of the phase and morphology on the electrorheological (ER) effect were investigated using an ER test. The ER results suggested that the ER efficiency was significantly enhanced after the second hydrothermal treatment, especially under a high external electric field strength. The enhancement in the ER efficiency was further studied using a dielectric spectrum analysis. It demonstrated that the faster response time and large permittivity difference obtained from the dielectric spectrum of TiO2 were responsible for the improvement in the ER effect.

Description and visualization of the highly dynamic behavior of the electrorheological effect

When an electrorheological fluid is located between two electrodes and an electrical voltage is applied to them, the particles in the fluid move and form chains along the electric field lines. This phenomenon is called the electrorheological effect. The exact behavior of the particles has not yet been studied completely. Some optical investigations of particle motion or behavior have been performed, but did not take into account the high dynamic range directly after the application of an electric field. This study is intended to help explain how the particles behave when they encounter an electric field and then try to align themselves with it. There is an investigation into how these chains develop in a microchannel within milliseconds. For this purpose, the particle behavior of the electrorheological fluid is investigated with high dynamic imaging using a microscope. A high-speed camera records videos of the first milliseconds at 3000 fps synchronously with the application of an electric field. The results provide a better understanding of the chain formation and particle behavior of the electrorheological effect in the high dynamic range and can be used for the design of electrorheological applications as well as simulations of the particle movement.

Alternating current response and visualization of electrorheological fluid

The electrorheological effect produced by an ER-Fluid with an applied electric field is not yet fully understood. However, it is significant to understand how the viscosity increases, and thus, the ER-Effect works to optimally design ER-Applications. In this article, the ER-Effect and its response to different voltage forms with varying frequencies within a miniature fluidic device are described and visualized using a microscope. The different pressure drops across the channel are measured. Problems such as long saturation times using microchannels in combination with low flow velocities are described and explained. An electric frequency dependence of the chain formation has been discovered and that the use of alternating current offers superior performance in comparison with direct current. The optimal operating point for achieving the largest possible pressure difference is from 5 to 10 Hz for square wave voltages. In this frequency range, the performance of the electrorheological effect is greater than using direct current. From approximately 10 Hz, the power decreases with increasing electric frequency. Above 20 Hz, direct current is superior to alternating current voltage, so is not recommended for use in this range.

Comparing the Electrorheological Effect of Polyhedral Silsesquioxane Cage Structures with Different Numbers of Cyanopropyl Functional Groups.

Previous research has shown that polyhedral oligomeric silsesquioxane (POSS) particles in silicone oil show electrorheological (ER) activity. The effect of the number of same functional groups attached to POSS cage structures on the ER activity of these structures is discussed in this article. Two compounds of the octahedral geometry (T8) of cyanopropyl POSS (cPOSS) were used for this investigation. One of the compounds (monofunctionalized cPOSS) was commercially available, and the other (octafunctionalized cPOSS) was synthesized. The effects of the number of cyanopropyl functional groups attached to the inorganic silicon–oxygen core structure of the POSS compounds on the rheological properties are demonstrated through steady flow and oscillatory tests. Particular attention is paid to how the number of cyano functional groups affects the behavior of these suspensions of cPOSS compounds in silicone oil under increasing electric field strength. The research also contributed answers to the effects of changing the concentration of the cPOSS particles in the suspension. The flow curve was described by the Herschel–Bulkley model, and the yield stress values were ascertained from the model. The dielectric characterization was also done to support the ER response results, which showed that the octafunctionalized compound gave a better response. The differences in the ER properties of these compounds have also been discussed with the tests.

High electrorheological effect in Bi1.8Fe1.2SbO7 suspensions

We report on the first experimental evidence of the electrorheological effect in suspensions of superfine pyrochlore-type Bi1.8Fe1.2SbO7 powders. Tensile-compressive and shear stress studies of the electrorheological fluids, with various filler contents, revealed an exceptionally high electrorheological effect in the materials – the tensile yield strength at 5kV/mm reached about 20kPa. The frequency dependencies of dielectric permittivity, dielectric loss tangent, and the conductivity of the suspensions with various filler contents allowed estimation of the dielectric permittivity values for superfine Bi1.8Fe1.2SbO7 particles at zero and infinite frequencies. The study reveals new oxide materials as promising fillers for electrorheological fluids.

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 ...

Experimental investigations on electrorheological properties of lubricating oils containing ionic liquid. Part. 1. Investigations with modified Brookfield DV-III Ultra Viscosimeter

The results of experimental investigations on electrorheological (ER) properties of lubricating oils which contain ionic liquids, are presented in this article. The investigations were carried out on the special stand which was projected for this aim. On this stand there was used the modified Brookfield viscosimeter. Electrorheological properties of two mixtures were tested, i.e., silicone damping liquid GP-1 which is polimethylsiloksane mixture containing 2% (v/v) of ionic liquid CJ 001, i.e., tetrafluoroboran 1-methyl-3-octyloxymethylimidazolium as well as base polialfaolefine oil PAO-6 which contains 2% (v/v) of ionic liquid CJ 008, i.e., trihexyltetradecylphosphonium bis(trifluoromethylsulfonyl)imide. Selection of components of both mixtures was based on the results of investigations of miscible and on evaluation of basic phys-chem properties. The investigations showed that the made mixtures have generated the ER effect, but it was short-lived effect, suggesting the changes of inner structure of these mixtures. Therefore, we have planned the next investigations, among others dielectric spectroscopy and microscope observations in situ of these mixtures in external electric fields. The aim of those investigations will be to record the fading ER effect and to understand this mechanism. Keywords: electrorheological effect, homogenous mixtures, lubricants, ionic liquids

Backflow Effect Enabling Fast Response and Low Driving Voltage of Electrophoretic E-ink Dispersion by Liquid Crystal Additives

Electrophoretic display encountered several challenges towards high frame rate applications, such as long response time and high driving voltage. In this study, liquid crystal additive doping can simultaneously increase the response speed by 2.8 times and reduce the driving voltage to half of the initial value of electrophoretic dispersion. The backflow effect of liquid crystal, which induces an inversely electrorheological effect and facilitates the reverse micelles’ dielectrophoretic separation, was suggested to be the main reason for the performance improvement. The proposed method is facile and effective which shows promising potential for fast response and low power consumption e-paper applications.

High-response electrorheological servo valve

The demand of more powerful and high-dynamic hydraulic actuators gives the servo valve as a control member an increasingly important role. The valve should provide the hydraulic actuator with sufficient volume flow over wide frequency range to achieve large strains at high operating frequencies. Here, the electrorheological effect as an electrohydraulic valve drive offers great potential. It converts the electrical input signal directly into a controlling mechanical quantity within a few milliseconds and provides theoretically unlimited strain. Thus, the electrorheological effect has the ability to increase the performance of conventional hydraulic systems. This work presents a two-stage servo valve with an electrorheological pilot stage. Furthermore, it introduces a model to describe the static and dynamic properties of the system. The model is validated on the basis of measurement results.

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.

Orientation of Layered Aluminosilicates Particles with a High Aspect Ratio in Paraffin under an Electric Field

The electrorheological effect intensity is significantly influenced by the strength of the structure formed in an electric field due to the orientation of dispersed phase particles with respect to force lines. The structural organization of the filler in an electric field has been studied by X-ray diffraction on paraffin films. Particles of layered aluminosilicates with a high aspect ratio and various morphology such as montmorillonite and halloysite, are used as fillers. The distinctions in the structure formation of fillers shaped as lamellae and tubes are demonstrated.

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.

Lyotropic Liquid Crystal as an Electrolyte Additive for Suppressing Self‐Discharge of Supercapacitors

AbstractSelf‐discharge severely constrains the application of supercapacitors for long‐term energy storage because it causes decay of cell voltage and loss of energy. So far, three pathways have been proposed for the self‐discharge of supercapacitors: i) ohmic leakage, ii) diffusion‐controlled self‐discharge, iii) faradaic reactions. However, solutions for mitigating the self‐discharge of supercapacitors are limited. Here, we choose lyotropic liquid crystal (LLC) as an electrolyte additive to suppress the self‐discharge of supercapacitors through the electrorheological effect of the LLC. The LLC formed by the assembly of a triblock copolymer Pluronic L64 in ion liquid [Bmim]BF4 exhibits dielectric anisotropy and can reorient in an electric field, causing increased viscosity and slower ion diffusion of the electrolyte. It is found that, by adding 5 % (vol%) LLC into TEMABF4/acetonitrile electrolyte, the self‐discharge rate at room temperature can be decreased by 32 % compared to supercapacitors without LLC. Furthermore, the LLC could reduce the self‐discharge rate of supercapacitors even at 50 °C due to its stability in a relatively wide temperature range.

Electric-field-aligned functionalized-layered double hydroxide/polyphenyl ether composite membrane for ion transport

Abstract To address the insufficient ion conductivity of hydroxide exchange membranes (HEMs) used in alkali membrane fuel cells (AMFCs), we present a series of aligned layered double hydroxide (LDH)/polyphenyl ether (PPO) composite membranes based on the electrorheological effect. The hexagonal LDH was functionalized with N-spirocyclic ammonium (ASU-LDH) to enhance the electrorheological effect of the ASU-LDH as well as improve the ion conductivity of the ASU-LDH. The aligned ASU-LDH/triple-cation-functionalized PPO (ASU-LDH/TC-PPO) composite membranes were prepared by applied-electric field. The effective electric-induced ion channels (EICs) were constructed by aligned ASU-LDH nanosheets in HEMs, which are distinctly observed by scanning electron microscope (SEM). Notably, these EICs-contained ASU-LDH/TC-PPO composite membranes exhibit the higher ion conductivity and alkaline stability than those of normal TC-PPO and ASU-LDH/TC-PPO membranes. It is worth noticing that these EICs are different with the traditional phase-induced ion channels, the EICs show the shorter ion transport distances and broader water channels in HEMs. Attributing to EICs, the longitudinal ion conductivity of aligned ASU-LDH/TC-PPO membrane shows 32.2% and 18.7% improvement compared to pristine TC-PPO and normal ASU-LDH/TC-PPO membrane. The maximum ion conductivity of the aligned ASU-LDH/TC-PPO composite membrane reaches to 109.8 mS/cm at 80 °C. The long-term stability test shows that the aligned ASU-LDH/TC-PPO membranes still exhibit enhancing alkali resistance (83.2%) in 1 M KOH at 80 °C for 500 h. In brief, this work provides a novel and effective approach to prepare high-performance HEMs.

Electrorheological Properties of α-Bi2O3 and Bi2O2CO3

Abstract—We have synthesized needle- and platelike α-Bi2O3 and Bi2O2CO3 nanoparticles. The bulk density of the α-Bi2O3 and Bi2O2CO3 powders is 8.5 and 6.9 g/cm3. The dielectric permittivity of α-Bi2O3 and Bi2O2CO3 has been calculated using dielectric permittivity and dielectric loss tangent dispersion measurements in the frequency range from 2.5 × 101 to 1 × 106 Hz for 40% suspensions (0.05 and 0.08 volume fractions of α-Bi2O3 and Bi2O2CO3, respectively) in PMS-300 polydimethylsiloxane. The value of e∞ has been found to be 5.4 for α-Bi2O3 and 4.9 for Bi2O2CO3. Dielectric spectra of the suspensions have been shown to exhibit no relaxation behavior in the frequency range studied. We have compared the effects of the shape and dielectric permittivity of the particles on the magnitude of the electrorheological effect in them. Using a simple polarization model, we have analyzed the effect of the dielectric characteristics of the filler material on the yield stress τ0 of the suspensions in electric fields from 0 to 4 kV/mm. Using a combination of rheometric and direct microscopic observations, we have explained the effect of the type of filler on the electrorheological effect: the Bi2O2CO3-based ERFs have higher shear and compressive yield stresses, whereas the α-Bi2O3-based ERFs have a higher tensile yield stress.