An organic/inorganic polyaniline-wrapped halloysite nanotube (PANI/HNT) composite was prepared by the in situ polymerization of aniline in the presence of a HNT dispersion. The physical properties of the resulting PANI/HNT composite were characterized by scanning electron microscopy, thermogravimetric analysis, and Fourier-transform infrared spectroscopy. This organic/inorganic composite particle was then dispersed in silicone oil as an electrorheological (ER) fluid, and its ER properties were examined using a Couette-type rotational rheometer equipped with a high-voltage generator. This novel halloysite composite-based ER fluid exhibited typical ER properties under an applied electric field. 相似文献
Surface-conductive particles consisting of a poly(methyl methacrylate) (PMMA) core and a polyaniline (PA)-coated shell were synthesized and adopted as suspended particles for electrorheological (ER) fluids. The PA-PMMA composite particles synthesized were monodisperse and spherical in shape. The PA-PMMA suspensions in silicone oil showed typical ER characteristics under an applied electric field. The PA-PMMA composite particles possess a higher dielectric constant and conductivity than the pure PA particle, within an acceptable conductivity range for ER fluids, but the PA-based ER fluid showed larger shear-stress enhancement than the PA-PMMA-based systems. This phenomena can be explained by the interfacial polarizability of PA-based ER fluids, which is the difference between the ER fluid's dielectric constant and loss factor - this polarizability was higher than that of PA-PMMA-based ER fluids, as shown by the dielectric spectrum of each fluid. The insulating PMMA core suppressed the interfacial polarization in ER fluids, resulting in reduced interaction among particles under an imposed electric field. 相似文献
Silica-graphene oxide (Si-GO) hybrid composite particles were prepared by the hydrolysis of tetraethyl orthosilicate (TEOS) in the presence of hydrophilic GO obtained from a modified Hummers method. Scanning electron microscopy (SEM) and transmission electron microscopy (TEM) images provided visible evidence of the silica nanoparticles grafted on the surface of GO, resulting in Si-GO hybrid composite particles. Energy dispersive X-ray spectroscopy (EDX) and X-ray diffraction (XRD) spectra indicated the coexistence of silica and GO in the composite particles. The Si-GO hybrid composite particles showed better thermal stability than that of GO according to thermogravimetric analysis (TGA). The electrorheological (ER) characteristics of the Si-GO hybrid composite based ER fluid were examined further by optical microscopy and a rotational rheometer in controlled shear rate mode under various electric field strengths. Shear stress curves were fitted using both conventional Bingham model and a constitutive Cho-Choi-Jhon model. The polarizability and relaxation time of the ER fluid from dielectric spectra measured using an LCR meter showed a good correlation with its ER characteristics. 相似文献
A graphene oxide/titania (GO/TiO(2)) nanocomposite was fabricated by a facile electrostatic attraction method. With high polarization of GO particles and a relatively high dielectric constant of TiO(2) nanoparticles, the GO/TiO(2) nanocomposite is observed to be a potential electro-responsive electrorheological material under an applied electric field. 相似文献
Polyaniline (PANI) was synthesized via oxidative coupling polymerization in acid conditions and de-doped in solution of ammonia. The electrorheological (ER) properties of the PANI/silicone oil suspensions were investigated in oscillatory shear as functions of electric field strength, particle concentration, and host fluid viscosity. Consistent with literature, the PANI ER fluid exhibits viscoelastic behavior under the applied electric field and the ER response is strongly enhanced with increasing electric field strength and particle concentration. The dynamic moduli, G' and G' increase dramatically, by 5 orders of magnitude, as the electric field strength is increased to 2 kV/mm. A viscoelastic liquid to solid transition occurs at a critical electric field strength, in the range Ec = 50-200 V/mm, whose value depends on particle concentration and host fluid viscosity. The fibrillar structure formed in the presence of the applied field has a static yield strength tau(y), whose value scales with electric field strength as tau(y) approximately E(1.88). When the field is switched off a residual structure remains, whose yield stress increases with the strength of the applied field and particle concentration. When the applied stress exceeds the yield stress of the residual structure, fast, fully reversible switching of the ER response is obtained. 相似文献
Semiconducting camphorsulfonic acid doped polyaniline (PANI–CSA) particles were synthesized by chemical oxidation polymerization,
and their chemical structure and particle size were examined via Fourier transform IR spectroscopy and scanning electron microscopy,
respectively. Electrorheological (ER) fluids were prepared by dispersing the PANI–CSA particles in silicone oil, and their
steady-shear rheological properties under electric fields were investigated using a rotational rheometer with a high-voltage
generator. The PANI–CSA synthesized in this study possesses typical ER behavior:shear stress increases with increasing electric
field strengths.
Received: 31 August 2000 Accepted: 6 April 2001 相似文献
Cellulose, as a natural polymer with an abundant source, has been widely used in many fields including the electric field responsive medium that we are interested in. In this work, cellulose micron particles were applied as an electrorheological (ER) material. Because of the low ER effect of the raw cellulose, a composite particle of cellulose and Laponite was prepared via a dissolution–regeneration process. Scanning electron microscopy (SEM), Fourier-transform infrared spectroscopy (FT-IR) and X-ray diffraction (XRD) were used to observe the morphologies and structures of the composite particles, which were different from pristine cellulose and Laponite, respectively. The ER performances of raw cellulose and the prepared composite were measured by an Anton Paar rotational rheometer. It was found that the ER properties of the composite were more superior to those of raw cellulose due to the flake-like shapes of the composite particles with rough surface. Moreover, the sedimentation stability of composite improves drastically, which means better suspension stability. 相似文献
Hollow globular clusters of titanium oxide (TiO2) nanoparticles were synthesized by a simple hydrothermal method. The prepared particles were consequently coated by in situ
polymerization of conductive polymer polypyrrole (PPy) to obtain novel core–shell structured particles as a dispersed phase
in electrorheological (ER) suspensions. The X-ray diffraction analysis and scanning electron microscopy provided information
on particle composition and morphology. It appeared that PPy coating improved the compatibility of dispersed particles with
silicone oil which results in higher sedimentation stability compared to that of mere TiO2 particles-based ER suspension. The ER properties were investigated under both steady and oscillatory shears. It was found
that TiO2/PPy particles-based suspension showed higher ER activity than that of mere TiO2 hollow globular clusters. These observations were elucidated well in view of their dielectric spectra analysis; a larger
dielectric loss enhancement and faster interfacial polarization were responsible for a higher ER activity of core–shell structured
TiO2/PPy-based suspensions. Investigation of changes in ER properties of prepared suspensions as a function of particles concentration,
viscosity of silicone oil used as a suspension medium, and electric field strength applied was also performed. 相似文献
The rod-like titanium dioxide (TiO2) particles were synthesized by a simple and rapid microwave-assisted molten-salt method. The X-ray diffraction analysis revealed the phase composition transformation from the anatase phase of original TiO2 nanomaterial to the rutile phase of high crystallinity. Scanning electron microscopy proved the conversion of originally globular particles of original anatase TiO2 sized from 200 to 500 nm into rods with a length of 5–10 μm and a diameter between 0.5 and 2 μm. The electrorheological (ER) measurements performed under steady-state flow as a function of the applied electric field strength and particle concentration showed that suspended rutile rod-like TiO2 particle-based fluid exhibits much higher ER activity than that of original anatase TiO2 material powder. These observations were clearly demonstrated by viewing their dielectric spectra analyses. 相似文献
The effect of dielectric loss on the electrorheological (ER) characteristic of dielectric nanofluids under shear was studied. When nanofluids are activated by an applied electric field, it behaves like a non-Newtonian fluid under ER effect by creating the chains of nanoparticles. ER characteristics of ZnO and Al2O3 nanofluids with various nanoparticles concentration (0.1, 0.05, 0.01 wt%) were measured. For this purpose, a solenoid-based electromagnetic (EM) transmitter was used under different propagation media including air, tap water, and salt water. The result shows that all the nanofluids exhibit pseudo-plastic behavior, while the electric field causes a significant increase in viscosity in the presence of tap water, followed by salt water. Additionally, the viscosity of nanofluid shows a high dependence on particle loading. A possible mechanism was also proposed to describe the effect of dielectric properties on the ER behavior of dielectric nanofluids. 相似文献
A metal-organic framework, Cu(3)(BTC)(2), was synthesized and applied as an electro-responsive electrorheological material dispersed in insulating oil. Powder of crystalline Cu(3)(BTC)(2) exhibited excellent chain-like structures and controllable rheological properties in an applied electric field. 相似文献
A custom designed vertical oscillation rheometer (VOR) is used for the rheological measurements of electrorheological (ER) fluids consisting of 15 and 20 vol.% semiconducting polyaniline particles suspended in silicone oil. The viscoelastic material functions, including complex viscosity and complex shear modulus, are measured via geometric parameters, measured force, and applied strain of the VOR. Viscoelastic properties of the ER fluids are also measured as a function of applied electric field strength and particle concentration. The VOR, equipped with a high voltage generator, can easily be constructed and used to measure ER properties. It is further found that polyaniline suspensions behave as viscoelastic materials in an electric field. In linear viscoelastic conditions, elasticity was promoted with the increment of electric field due to particle chain structure in the presence of the applied electric field. It is also found that the applied electric field rather than particle concentration enhanced the elasticity of ER fluids. 相似文献
We have studied the effect of an external direct current (DC) electric field ( approximately 1 kV/mm) on the rheological properties of colloidal suspensions consisting of aggregates of laponite particles in a silicone oil. Microscopy observations show that, under application of an electric field greater than a triggering electric field Ec approximately 0.6 kV/mm, laponite aggregates assemble into chain- and/or columnlike structures in the oil. Without an applied electric field, the steady-state shear behavior of such suspensions is Newtonian-like. Under application of an electric field larger than Ec, it changes dramatically as a result of the changes in the microstructure: a significant yield stress is measured, and under continuous shear the fluid is shear-thinning. The rheological properties, in particular the dynamic and static shear stress, were studied as a function of particle volume fraction for various strengths (including null) of the applied electric field. The flow curves at constant shear rate can be scaled with respect to both the particle fraction and electric field strength onto a master curve. This scaling is consistent with simple scaling arguments. The shape of the master curve accounts for the system's complexity; it approaches a standard power-law model at high Mason numbers. Both dynamic and static yield stresses are observed to depend on the particle fraction Phi and electric field E as PhibetaEalpha, with alpha approximately 1.85 and beta approximately 1 and 1.70 for the dynamic and static yield stresses, respectively. The yield stress was also determined as the critical stress at which there occurs a bifurcation in the rheological behavior of suspensions that are submitted to a constant shear stress; a scaling law with alpha approximately 1.84 and beta approximately 1.70 was obtained. The effectiveness of the latter technique confirms that such electrorheological (ER) fluids can be studied in the framework of thixotropic fluids. The method is very reproducible; we suggest that it could be used routinely for studying ER fluids. The measured overall yield stress behavior of the suspensions may be explained in terms of standard conduction models for electrorheological systems. Interesting prospects include using such systems for guided self-assembly of clay nanoparticles. 相似文献
We report the successful synthesis of transparent thin film of conducting poly(3,4‐ethylenedioxythiophene)/poly(styrenesulfonic acid) (PEDOT/PSS) coated monodisperse polystyrene (PS) microspheres via a simple physical adsorption route in an aqueous media and their electrorheological (ER) application under an applied electric field. Due to the insulating PS core, the PEDOT/PSS wrapped PS (PEDOT/PSS/PS) particles possess a low volume conductivity appropriately applied as ER active materials. Tested by a rotational rheometer under an applied electric field, the PEDOT/PSS/PS based ER fluid dispersed in a silicone oil shows a typical Bingham‐fluid behavior with increased yield stresses according to the increase of electric field strength.
The objective of this article is to give a review of electrorheological (ER) suspensions whose rheological properties can abruptly change under an external electric field. Attention is given to the physical backgrounds behind ER phenomena reported recently. The criteria on how to design a high performance ER fluid and mechanisms explaining how an ER suspension displays the ER effect are focused upon. We begin with a brief historic introduction, ER materials, followed by positive ER effect, negative ER effect and photo-ER effect discussions. The physical parameters that can substantially affect the ER effect are discussed thereafter, and physical processes occurring in ER suspensions under an electric field are reviewed. The mechanisms of the ER effect proposed before are summarized. A future outlook on the ER material development and ER fluid applications is given. 相似文献
One 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. 相似文献