Electrorheological Activity Research Articles

Effects of promoter and dedoping process on electrorheological response of polyaniline-graft-chitosan copolymer

In this study, electrorheological (ER) properties of biodegradable and conducting polyaniline-graft-chitosan (PAni-g-CS) copolymer particles were investigated. For this purpose, PAni and PAni-g-CS particles were synthesized by using in situ oxidative radicalic polymerization method. At first, PAni and PAni-g-CS/silicone oil (SO) ER suspensions (15% V/V) were subjected to external electric field and they exhibited low ER activity. When the external electric field strengths ([Formula: see text] were increased, both the suspensions showed electrical breakdown. Therefore, virgin PAni and PAni-g-CS were first subjected to dedoping process by treating with 1.0 M NaOH(aq) and non-ionic surfactant Triton X-100 (T-X) surfactant to enhance the expected ER activity and prevent the electrical breakdown. But we observed that the addition of T-X as promoter had no significant effect on the ER activity. On the other hand, electric filed-induced viscosities of both the suspensions were observed to enhance after the dedoping (DD) process and electrical breakdown prohibited. After the DD process, DD PAni-g-CS/SO ER system exhibited the highest electric field-induced viscosity by reaching 400[Formula: see text]Pa[Formula: see text]⋅[Formula: see text]s at [Formula: see text][Formula: see text]kV/mm. The highest ER efficiency was also obtained for DD PAni-g-CS/SO system at 15% (V/V) as 79. Additionally, typical shear thinning non-Newtonian viscoelastic behavior was observed under externally applied E. The conduction model of DD PAni-g-CS/SO system was determined to well fit the conduction model by showing a slope of [Formula: see text] calculated from the E vb. yield stress graph. In conclusion, conducting and biodegradable-dedoped PAni-g-CS particles would be a good candidate for potential ER applications as dry-based ER materials having high colloidal stability of 76%.

A Water-Free Ionic Covalent Organic Polymer with High Electrorheological Activity and Temperature Stability

Ionic polymers are important electrorheological (ER) materials, whose ER effect originates from ion motion-induced interfacial polarization. However, the first-generation ionic polymer ER material based on traditional polyelectrolyte needs adsorbed water to make ion movement to activate the ER effect. This results in poor temperature and cycling stability. Although the second-generation ionic polymer ER material based on polyethylene oxide-salt complexes and the currently developed poly(ionic liquid) ER material do not require adsorption of water to activate the ER effect due to decreased ion-pair dissociation energy, low glass transition temperature still limits their temperature and cycling stability. Herein, we report an ionic polymer ER material based on ionic covalent organic polymer (iCOP) synthesized via the Menshutkin reaction and ion exchange, which exhibits not only a highly anhydrous ER effect due to lots of hydrophobic fluoric counterion-induced strong interfacial polarization but also excellent temperature stability and cycling stability due to a unique covalent organic framework structure. In particular, its leaking current density and power consumption are far lower than those of the ER system of traditional polyelectrolytes, polyethylene oxide-salt complexes, and poly(ionic liquid)s. These make iCOP possess large potential as a platform to develop next-generation ionic polymer ER material with high performance.

Morphology-controlled stabilised polyaniline nanoparticles and their electrorheological properties

Nanoparticles and sub-microparticles of the conducting polymers polyaniline (PANI), polyanisidine (PoANIS) and their copolymers were synthesised, deprotonated and dispersed in viscous media in order to study the influence of their synthetic conditions and of steric stabilisers (cellulose-based materials) on the physical, chemical and morphological characteristics of the polymers. Electrorheological (ER) measurements were performed and related to the polymer properties. The polymer particles had various loadings of stabilisers, depending on the polymer/stabiliser interactions and the stabiliser concentration. When stabilised with hydroxyethylcellulose (HEC), the PANI particles contained traces of HEC, while PoANIS, less stabilised by the electron-rich HEC molecules, did not. Stabilised PANI-HEC synthesised at 0°C readily formed small fibres that, when deprotonated, displayed a large electrorheological response (yield stress ca. 800 Pa at 3.2 kV.mm−1). PoANIS prepared under the same conditions yielded a polydisperse cenospheric material with no ER activity.

Hollow TiO2 Nanoparticles Capped with Polarizability-Tunable Conducting Polymers for Improved Electrorheological Activity.

Hollow TiO2 nanoparticles (HNPs) capped with conducting polymers, such as polythiophene (PT), polypyrrole (PPy), and polyaniline (PANI), have been studied to be used as polarizability-tunable electrorheological (ER) fluids. The hollow shape of TiO2 nanoparticles, achieved by the removal of the SiO2 template, offers colloidal dispersion stability in silicone oil owing to the high number density. Conducting polymer shells, introduced on the nanoparticle surface using vapor deposition polymerization method, improve the yield stress of the corresponding ER fluids in the order of PANI < PPy < PT. PT-HNPs exhibited the highest yield stress of ca. 94.2 Pa, which is 5.0-, 1.5-, and 9.6-times higher than that of PANI-, PPy-, and bare HNPs, respectively. The improved ER response upon tuning with polymer shells is attributed to the space charge contribution arising from the movement of the charge carriers trapped by the heterogeneous interface. The ER response of studied ER fluids is consistent with the corresponding polarizability results as indicated by the permittivity and electrophoretic mobility measurements. In conclusion, the synergistic effect of hollow nanostructures and conducting polymer capping effectively enhanced the ER performance.

Low-filled suspensions of α-chitin nanorods for electrorheological applications

Highly anisometric α-chitin nanoparticles isolated by TEMPO-oxidation were investigated as filler for electrorheological fluids. The dimensions of rod-like particles were determined by AFM and cryo-TEM methods. The rheological behavior of α-chitin nanoparticles in polydimethylsiloxane changes from viscous to elastic under electric field. The yield stress reaches about 220 Pa at 7 kV/mm for 1.0 wt% fluid. Despite the nanosize of particles, the suspensions sedimentation ratio was found to be low (~23%). The electrorheological behavior of the fluids was discussed in terms of the Mason numbers. The stability of fluids response under switching electric field was shown. The activation energy of polarization processes in suspensions was calculated as 58 ± 2 and 64 ± 1 kJ/mol for 0.5 and 1.0 wt% filler content from the impedance spectra. The high aspect ratio (~70) and dielectric permittivity result in high electrorheological activity of α-chitin suspensions at extremely low concentrations (≤1.0 wt%).

Enhanced electrorheological activity of porous chitosan particles

Novel porous filler for electrorheological fluids was fabricated from chitosan via freeze drying technique. An exceptional electrorheological effect was discovered in suspensions of polydimethylsiloxane (silicone oil) filled by highly porous chitosan particles. The electrorheological activity was studied by rotational rheometry and visualized by optical microscopy. High porosity of the filler allows preparing highly efficient electrorheological fluids at rather low (< 1 wt%) concentration of dispersed phase. The mechanism of chain-like structure formation was considered. The electrorheological behavior of suspensions and the filler structural organization at different concentration were comprehended in terms of dielectric properties. The rheological data were approximated by Bingham and Cho-Choi-Jhon equations. The sedimentation stability of chitosan suspensions in polydimethylsiloxane was significantly affected by particles porosity.

Analysis of the flow behavior of electrorheological fluids containing polypyrrole nanoparticles or polypyrrole/silica nanocomposite particles

A four-parameter model (Seo-Seo model) was used to analyze the flow behavior of some electrorheological (ER) fluids containing polypyrrole (PPy) nanoparticles, nanocomposite particles of conductive polypyrrole confined in mesoporous silica (MCM-41), and core-shell-structured SiO2/polypyrrole nanoparticles. The static yield stress predictions by the model were compared with the experimental data and dynamic yield stress obtained from the Bingham model and/or Cho-Choi-Jhon (CCJ) model. The static yield stress values were larger than the dynamic yield stress values. It was also found that the static yield stress of the polypyrrole suspension had a quadratic dependence on the electric field strength as predicted by the electric polarization model whereas those of the nanocomposite suspensions showed 1.5 power-law dependency. A master curve describing the yield stress data dependence on the electric field strength was obtained using a single-parameter scaling function to interpret the underlying mechanism of ER activity. A simple method for evaluating the activity mechanism criterion has been proposed and applied to the ER response of those three kinds of suspension. The results show that the critical electric field strength should be checked before the conduction mechanism is asserted, even if the yield stress plot shows 1.5 power-law dependence on the electric field strength.

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.

Polyaniline (PANI) and BaTiO3 composite nanotube with high suspension performance in electrorheological fluid

In this research, one-dimensional polyaniline/barium titanate (PANI/BaTiO3) composite nanotubes with core-shell structure were synthesized by hydrothermal treatment, and the surfaces of the nanocomposites were modified with 3-aminopropyltriethoxysilane. The TGA measurement results showed the thermal stability of this nanocomposite was improved compared with pure polyaniline, indicating the deposition of polyaniline on the surface of BaTiO3 nanotubes, which was confirmed by the characterizations and morphology analyses of SEM, FTIR, and XRD. Furthermore, a new electrorheological (ER) fluid was obtained by dispersal of polyaniline/barium titanate nanotubes in silicone oil by ultrasonic mixing technique. The nanotube-based ER fluid exhibited higher suspension stability than original nanoparticle ER fluid. Only insignificant sedimentation was found in this nanotube suspension even several months later. This fluid showed a notable ER behavior with the electric field affection, which was caused by the microstructure change induced by polarization among nanotubes; these observations were well interpreted by analyses of the flow curve, static yield stress, and dynamic test. The results of this study provide possible ways to synthesize ER fluid with good suspension stability and high ER activity by 1-D nanotubes and would help to investigate the potential application of ER fluid in practical realm of waste water treatment.

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.

Electrorheological Effects of Synthesized Octa-cyanopropylsilsesquioxane Cage Structure.

This article introduces a new electrorheological (ER) fluid. A molecular cage structure for electrorheological applications has been synthesized, and the ER behavior of the octa-functionalized polyhedral oligomeric silsesquioxane (POSS) variant in silicone oil (PDMS) has been shown. The hydrolyzation route has been used in the synthesis, the microstructure has been displayed using scanning electron microscopy, the yield has been ascertained, and the compound has been characterized. The rheological properties are demonstrated on the ER fluid through steady flow and oscillatory tests to investigate the effects of change in concentration on the functional group attached to the inorganic silicon–oxygen core structure of the POSS compound. The electrorheological efficiency was analyzed, and dielectric characterization was done. The flow curve was described by the Herschel–Bulkley model, and yield stress values were derived from the model. The octa-cyanoPOSS/PDMS electrorheological fluid has been shown to have ER activity.

Effect of surfactant on the dielectric and electrorheological properties of zinc borate/silicone oil dispersions

Zinc borate (ZB) particles dispersed in silicone oil (SO) at concentrations of ϕ = 5vol%-20vol% were subjected to dielectric analysis to elucidate their polarization strength, time, and mechanism. Results revealed that all virgin dispersions lacked polarization. Triton X-100, a non-ionic surfactant, was added to ZB/SO dispersions to enhance the polarizability of ZB particles. The addition of 1vol% Triton X-100 enhanced the polarizability of ZB/SO dispersions, and the 15vol%ZB/SO system provided the highest dielectric difference Δe′ (the difference in e′ values at zero and infinite frequency, Δe′ = e0 - e221D) of 3.64. The electrorheological (ER) activities of the ZB/SO/Triton-X dispersion system were determined through the ER response test, and viscoelastic behaviors were investigated via oscillation tests. A recoverable deformation of 36% under an applied electrical field strength of 1.5 kV/mm was detected through creep and creep recovery tests.

Engineering the morphology of TiO2/carbon hybrids via oxidized Ti3C2Tx MXene and associated electrorheological activities

Well defined morphology of titanium dioxide/carbon (TiO2/C) hybrids provides intriguing physical chemical properties, thus, they are attractive for broadly specific applications. However, the conventional wisdom of rational design of TiO2/C hybrids has not been satisfactorily investigated especially in nanostructure mainly due to the heterogeneous interface barriers between TiO2 and carbon. Herein, we present a completely novel yet generalized approach for the fabrication of TiO2/C hybrids with tunable bio-inspired shapes (e.g., grape-like, echeveria-like, albizia-like, bamboo-type, chestnut-like, etc.) based on a versatile solvothermal technique. To reduce interfacial barriers between TiO2 and carbon layers, the TiO2 nanoparticles are firstly decorated on the conductive carbon layers via an in-situ CO2 oxidation of Ti3C2Tx MXene (c-TiO2/C). The TiO2 arrays are heteroepitaxially grown on the c-TiO2/C substrate, which serves simultaneously as the TiO2 crystal seeds and carbon sources. A series of bio-inspired TiO2/C hybrids with desired constituent nano-units (including nanoplates, nanorods, nanoribbons, and nanowires) are facilely achieved via simply tuning the amounts and calcination temperatures of c-TiO2/C along with the hydrothermal time. More interestingly, the introduction of lithium ions can split the TiO2 arrays into small pieces, which is highly beneficial for the design of TiO2/C hybrids with preferred architectures. A detailed growth mechanism of the achieved TiO2/C hybrids is also proposed. Additionally, these TiO2/C hybrids provide valuable applications in many fields, such as sensing, catalysis and energy storage. Take the electro-responsive activity as an example, the achieved TiO2/C hybrids with tailored morphologies demonstrate tunable electro-rheological (ER) performances. The design principle is generally applicable to other metal (M) oxides/C systems, which will provide excellent opportunities for designing advanced material systems with widespread multifunctional applications.

Electrorheological behaviour of suspensions in silicone oil of doped polyaniline nanostructures containing carbon nanoparticles

Electrorheological fluids have been paying a lot of attention due to their potential use in active control of various devices in mechanics, biomedicine or robotics. An electrorheological fluid consisting of polarizable particles dispersed in a non-conducting liquid is considered to be one of the most interesting and important smart fluids. This work presents the effect of the dopant, camphorsulphonic acid or citric acid, on the electrorheological behaviour of suspensions of doped polyaniline nanostructures dispersed in silicone oil, revealing its key role. The influence of carbon nanoparticle concentration has also been studied for these dispersions. All the samples showed an electrorheological effect, which increased with electric field and nanostructure concentration and decreased with silicone oil viscosity. However, the magnitude of this effect was strongly influenced not only by carbon nanoparticle concentration but also by the dopant material. The electrorheological effect was much lower with a higher carbon nanoparticle concentration and doped with citric acid. The latter is probably due to the different acidities of the dopants that lead to a different conductivity of polyaniline nanostructures. Furthermore, the effect of the carbon nanoparticles could be related to its charge trapping mechanism, while the charge transfer through the polymeric backbone occurs by hopping. Polyaniline/camphorsulphonic acid composite nanostructures dispersed in silicone oil exhibited the highest electrorheological activity, higher than three decades increase in apparent viscosity for low shear rates and high electric fields, showing their potential application as electrorheological smart materials.

Preparation of core-shell structured metal-organic framework@PANI nanocomposite and its electrorheological properties.

A novel core–shell-type electrorheological (ER) composite material was fabricated via using polyaniline as an insulating layer to the outer surface of the core conductive metal–organic framework (MIL-125) with controlled size and morphology. MIL-125 was firstly synthesized by a solvothermal method, and then polyaniline was synthesized in a polar solvent and a tight coating was successfully achieved to form a MIL-125@PANI core–shell nanocomposite. This core–shell structure greatly enhances the polarization ability of dispersed particles, thereby improving their rheological properties. The morphology of pure MIL-125 and MIL-125@PANI has been characterized by transmission electron microscopy (TEM) and scanning electron microscopy (SEM). Their structure was characterized by X-ray powder diffraction. Moreover, the ER activity of MIL-125-based and MIL-125@PANI-based ER fluids by dispersing the particles into silicone oil was studied using a rotational rheometer. The results show that the MIL-125@PANI composite particles have higher ER properties.

Synthesis and Physicochemical and Electrorheological Properties of Modified Nanodisperse Titanium Dioxide

Nanodisperse modified titanium dioxide ranging in specific surface from 70 to 130 m2/g has been prepared by a sol–gel process using Al(NO3)3 and H3PO4 as modifying components and dodecylamine and ammonium carbonate as structuring components. Microwave drying of an intermediate product and pulverization in a planetary mill have been shown for the first time to be effective in reducing the bulk density of the material and improving its electrorheological activity. The effect of filler concentration (10–40 wt %) on the shear load and leakage current density of electrorheological dispersions has been examined.

Porous TiO2 Nanoparticles Derived from Titanium Metal–Organic Framework and Its Improved Electrorheological Performance

A simple method for synthesis of porous TiO2 nanoparticles was developed via a two-step route using titanium metal–organic framework (MOF) as a precursor, in which MOFs were first prepared by a cetyltrimethylammonium bromide (CTAB) assisted solvothermal method and then calcined in air at 500 °C. After pyrolysis of precursor MOFs, the anatase TiO2 inherited the porosity of precursor MOF and possessed a large surface area and uniform pore distribution, which was subsequently adopted as an electrorheological (ER) material by dispersing in silicone oil. ER activities of MOFs and porous TiO2 based suspensions under the applied electric fields were investigated in a controlled shear rate (CSR) mode. In contrast to MOFs based ER fluids, the suspension of porous TiO2 exhibited a higher ER efficiency and lower leakage current. Furthermore, the improvement of dielectric properties was found to be responsible for the enhanced ER activity through an investigation of dielectric spectrum.

Electrorheological Fluids with High Shear Stress Based on Wrinkly Tin Titanyl Oxalate.

Electrorheological (ER) fluids are considered as a type of smart fluids because their rheological characteristics can be altered through an electric field. The discovery of giant ER effect revived the researchers' interest in the ER technological area. However, the poor stability including the insufficient dynamic shear stress, the large leakage current density, and the sedimentation tendency still hinders their practical applications. Herein, we report a facile and scalable coprecipitation method for synthesizing surfactant-free tin titanyl oxalate (TTO) particles with tremella-like wrinkly microstructure (W-TTO). The W-TTO-based ER fluids exhibit enhanced ER activity compared to that of the pristine TTO because of the improved wettability between W-TTO and the silicone oil. In addition, the static yield stress and leakage current of W-TTO ER fluids also show a fine time stability during the 30 day tests. More importantly, the dynamic shear stress of W-TTO ER fluids can remain stable throughout the shear rate range, which is valuable for their use in engineering applications. The results in this work provided a promising strategy to solving the long-standing problem of ER fluid stability. Moreover, this convenient route of synthesis may be considered a green approach for the mass production of giant ER materials.

Facile fabrication of polyaniline/polypyrrole copolymer nanofibers with a rough surface and their electrorheological activities

ABSTRACTHierarchical polyaniline/polypyrrole (PANI/PPy) copolymer nanofiber was prepared via a two‐step method and adopted as dispersing materials for electrorheological (ER) fluids. The first step was used to synthesize PANI nanofibers by a rapid mixing method. Subsequently, the PANI/PPy copolymer nanofibers with a rough surface were obtained using an in situ polymerization method continuously. The morphology of the resultant PANI/PPy copolymer nanofibers can be controlled by varying the amount of Py monomer in the secondary in situ polymerization method. The rough surface of PANI/PPy copolymer nanofibers were confirmed by scanning electron microscopy and transmission electron microscopy. The diameter of PANI/PPy nanofiber is within the range 100–200 nm. The obtained PANI/PPy copolymer particles all exhibit amorphous structure through X‐ray diffraction measurement. We also demonstrated that the hierarchical PANI/PPy copolymer nanofibers exhibited characteristic ER behaviors, which were investigated using a Haake rotational rheometer at various electric field strengths. The ER efficiency e for PANI‐1mLPPy and PANI‐2mLPPy ER fluids at shear rate 0.1 s−1 is 36.6 and 28.5 under electric field strength E = 3 kV/mm, respectively. Low leaking current density is observed even at high electric field strength and wide plateau region appeared, which show a strong ER activity for the PANI/PPy composite nanofibers. The results also indicate that the PANI/PPy composite particles have distinctly enhanced ER effect compared with the pure PANI and PPy particles under electric stimuli. The significantly improved ER property of PANI/PPy‐based ER fluid is ascribed to the enhanced interfacial polarization. © 2018 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2018, 135, 46289.

Switchable electrorheological activity of polyacrylonitrile microspheres by thermal treatment: from negative to positive.

The study focuses on the effect of thermal deformation degree of polyacrylonitrile (PAN) particles on the electrorheological (ER) properties of their suspensions. The heat-treated PAN particles are manufactured as ER materials using a thermocatalytic processes. The molecular structures of ER materials are analyzed to confirm a stabilization or a carbonization degree. We categorized the prepared ER particles into three basic types according to their deformation degree: Thermal dried PAN, stabilized PAN, and pre-carbonized PAN. The raw, stabilized, and pre-carbonized PAN particle-dispersed suspensions showed positive ER properties. The ER properties are enhanced as the heat-treatment temperature increases due to improved dielectric property. However, the thermal dried PAN particle ER suspensions showed negative ER behavior though the particles have higher conductivity and dielectric constants than those of the host fluid, which is contrary to the conduction model. XRD results indicate that the ER materials could show contradictory ER behavior even if they have the same molecular structures due to their crystallinity. This discovery is expected to boost the development of both positive ER and negative ER suspensions based on carbonaceous ER materials.