Effect of polymerization temperature on polyaniline based electrorheological suspensions

As one of the intrinsically polarizable materials used in electrorheological (ER) fluid, polyaniline was synthesized by the chemical oxidation of aniline with ammonium peroxysulfate. ER fluids were prepared by dispersing polyaniline particles in silicone oil, and their rheological properties were measured. The effect of the polymerization temperature of polyaniline on its ER characteristics was investigated. ER fluids with polyaniline particles synthesized at −10°C (PA-10) showed the best ER performance (yield stress) compared with those synthesized at higher temperatures. A difference in the flow behavior of the ER fluids was also investigated through the dielectric spectra of ER fluids. Received: 24 March 1988 Accepted: 3 August 1998     

Electrorheological characteristics of polyaniline/titanate composite nanotube suspensions

In this paper, one-dimensional polyaniline/titanate (PANI/TN) composite nanotubes were synthesized by in situ chemical oxidative polymerization directed by block copolymer. These novel nanocomposite particles were used as a dispersed phase in electrorheological (ER) fluids, and the ER properties were investigated under both steady and dynamic shear. It was found that the ER activity of PANI/TN fluids varied with the ratio of aniline to titanate, and the PANI/TN suspensions showed a higher ER effect than that made by sphere-like PANI/TiO₂ nanoparticles. These observations were well interpreted by their dielectric spectra analysis; a larger dielectric loss enhancement and a faster rate of interfacial polarization were responsible for a higher ER activity of nanotubular PANI/TN-based fluids.     

Dielectric spectroscopy on W/O emulsions under influence of shear forces

The dielectric properties of concentrated w/o-emulsions have been investigated, both at rest and during shear. The volume fraction water ranged from 0.50 to 0.95. The time domain dielectric spectroscopy techniques (TDS) was used to record the dielectric spectra, which covered the frequency region from 25 MHz to 2 GHz. In order to simultaneously record rheological and dielectric data a modified viscometer of the coaxial cylinder type was applied.A close connection between the viscosity and the dielectric properties of w/o emulsions is demonstrated. The very large effects of shear both on the static permittivity and the dielectric relaxation time for the emulsion can partially be ascribed to the degree of flocculation in the system. At high shear rates, at which the emulsions are expected to have a low degree of flocculation, the observed dielectric properties differ from those expected from a theoretical model for spherical emulsion droplets.     

Synthesis and Electrorheological Characterization of Polyaniline/Barium Titanate Hybrid Suspension

As organic/inorganic composites having attracted much attention due to their heterogeneous physical properties, conducting polyaniline (PANI) and barium titanate (BaTiO₃) which possesses large electronic resistance and excellent dielectric strength, were utilized to synthesize PANI/BaTiO₃ hybrid which is applicable for an electrorheological (ER) material via ‘in-situ’ oxidative polymerization. Physical properties of the obtained PANI/BaTiO₃ composites were characterized via Fourier-transform infrared spectra (FT-IR), thermogravimetry analysis (TGA), and scanning electron microscopy (SEM). The ER behaviors were investigated via a rotational rheometer, and their shear stresses were fitted using our previously proposed rheological equation of state.     

Synthesis and electrorheology of camphorsulfonic acid doped polyaniline suspensions

 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     

Electrorheology of aniline oligomers

Aniline oligomers were prepared by the oxidation of aniline with p-benzoquinone in aqueous solutions of methanesulfonic acid (MSA) of various concentrations. Their molecular structures were assessed by Fourier transform infrared spectroscopy. The electrorheological (ER) behavior of their silicone oil suspensions under applied electric field has been investigated. Shear stress at a low shear rate, τ _0.9, was used as a criterion of the rigidity of internal structures created by the application of an electric field. It was established from the fitting of the dielectric spectra of the suspensions with the Havriliak–Negami model that dielectric relaxation strength, as a degree of polarization induced by an external field contributing to the enhanced ER effect, increases and relaxation time, i.e., the response of the particle to the application of the field, decreases when a higher molar concentration of MSA is used. The best values were observed for suspensions of the sample prepared in the presence of 0.5 M of MSA. This suspension creates stiff internal structures under an applied electric field strength of 2 kV mm^?1 with τ _0.9 of nearly 50 Pa, which is even slightly of higher value than that obtained for standard polyaniline base ER suspension measured at the same conditions. The concentration of the MSA used in the preparation of oligomers seems to be a crucial factor influencing the conductivity, dielectric properties and, consequently, rheological behavior, and finally ER activity of their suspensions.     

The electrorheological efficiency of polyaniline particles with various conductivities suspended in silicone oil

Electrorheological (ER) behavior of silicone oil suspensions of particles of polyaniline protonated to various doping levels with ortho-phosphoric and tetrafluoroboric acids has been studied. The dynamic yield stress obtained by extrapolation of shear stress to zero shear rate using Herschel–Bulkley equation was used as a criterion of the ER efficiency. At a same molar concentration of doping acids, various protonation effects appeared and the dependences of the yield stress on the acid concentration differed. The comparison of the yield stresses with dielectric characteristics calculated from the Havriliak–Negami equation revealed that the particle conductivity, in contrast to particle permittivity, dominates the polarization process especially at higher protonation degrees. Consequently, particle conductivity or dielectric relaxation time proved to be the parameters providing the common dependences of the yield stress regardless of the way of polarization.     

Electrorheological behavior of suspensions of a substituted polyaniline with long alkyl pendants

The electrorheological (ER) properties of poly(2-dodecyloxyaniline) (PDOA) suspensions in silicone oil were investigated. The ER behavior of such suspensions of polyaniline particles depends on the type of stabilizer and doping or dedoping level. Here we report on the ER behavior of particles of a substituted polyaniline with long alkyl pendants. Rheological measurements were carried out using a rotational rheometer with high-voltage generator in both constant shear stress and rate modes. Suspensions of the as-synthesized polyaniline particles in silicone oil showed a substantial ER response.     

The enhancement of the oxidation resistance of carbonyl iron by polyaniline coating and consequent changes in electromagnetic properties

In order to enhance the stability of commercially unmodified processed carbonyl iron (CI) and to prevent corrosion, CI powders were coated with polyaniline (PANI) by using surfactant-stabilized PANI colloids in chloroform. PANI coats the individual particles with a film of a few micrometres thickness. Electromagnetic properties, as well as thermal and storage stability, of polymer composites filled with pristine and PANI-coated CI have been studied. The PANI overlayer has negligible influence on the magnetic and dielectric spectra of CI-filled polymer composites at ambient temperature. However, the temperature-frequency study of complex permittivity demonstrated that the composites containing PANI-coated CI powders are characterized by temperature-independent dielectric spectra, whereas the complex permittivity of polymer composites with pristine powders drastically decreased at elevated temperature. Additionally, the thermogravimetric analysis of pristine and PANI-coated CI powders in air has shown improvement in the stability. PANI overlayer prevents the oxidation of particles and acts as corrosion protection of CI.     

Rheological and electrical properties of polypropylene/MWCNT composites prepared with MWCNT masterbatch chips

Melt compounded PP/MWCNT (polypropylene/multi-walled carbon nanotube) composites were prepared by diluting highly concentrated masterbatch chips. Maleic anhydride grafted polypropylene (PP-g-MAH) was used as a compatibilizer to promote dispersion and interaction of MWCNTs. Rheological properties were investigated with respect to the MWCNT and compatibilizer loadings, and related to morphological and electrical properties. As the MWCNT loading was increased, shear viscosity and yield stress were increased at low shear rate region because of increased interaction between MWCNT particles. When the MWCNT loading was low, MWCNT dispersion was improved by the PP-g-MAH compatibilizer because MWCNTs were wetted sufficiently due to the presence of the compatibilizer. However, rheological and electrical properties of highly concentrated MWCNT composites with the compatibilizer were not improved compared with PP/MWCNT composites without the compatibilizer because the compatibilizer did not provide sufficient wrapping of MWCNT particles. Electrical and morphological properties of PP/MWCNT composites were correlated with the rheological properties in steady and dynamic oscillatory shear flows.     

ELECTRORHEOLOGICAL PROPERTIES OF POLYANILINE/PUMICE COMPOSITE SUSPENSIONS

Electrorheological （ER） properties of polyaniline （PAni）, pumice and polyaniline/pumice composites （PAPC） were investigated. Polyaniline and PAni/pumice composite were prepared by oxidative polymerization. PAni/pumice particlesbased ER suspensions were prepared in silicone oil （SO）, and their ER behavior was investigated as a function of shear rate, electric field strength, concentration and temperature. Sedimentation stabilities of suspensions were determined. It has been found that ER activity of all the suspensions increases with increasing electric field strength, concentration and decreasing shear rate. It has shown that the suspensions have a typical shear thinning non-Newtonian viscoelastic behavior. Yield stress of composite suspensions increased linearly with increasing applied electric field strength and with concentrations of the particles. The effect of high temperature on ER activity of purrfice/silicone oil systems was also investigated.     

Electrorheological characteristics of polyaniline and its copolymer suspensions with ionic and nonionic substituents

Electrorheological (ER) characteristics of ER fluids, composed of suspensions of semiconducting polyaniline and two different copolyaniline particles in silicone oil, were determined experimentally. Ionic sodium diphenylamine sulfonate and nonionic o-ethoxyaniline were used to synthesize copolyanilines, i.e. N-substituted copolyaniline and poly(aniline-co-o-ethoxyaniline), respectively. ER fluids composed of these three different polymers were compared with respect to their rheological properties under an applied electric field. It was found that ER fluids containing a copolymer with an ionic group exhibited the highest ER performance among polyaniline and its copolymer systems in a shear-rate region above 1 s⁻¹. Received: 22 February 1999 /Accepted in revised form: 25 August 1999     

Spectral characteristics of polyaniline nanostructures synthesized by using cyclic voltammetry at different scan rates

The polyaniline nanofibers with different sizes were synthesized by using cyclic voltammetry at different potential scan rates, in the presence of ferrocenesulfonic acid. The potential scan rate controlled the formation and growth of polyaniline nuclei, which plays a key role in controlling nanofiber sizes. The average diameters of nanofibers decreased from about 130 nm to about 80 nm as the potential scan rate increased from 6 to 60 mV s (-1). We first observed an ordered change in the following spectra with the nanofiber sizes of polyaniline. The spectra of the X-ray diffraction indicated that the partially crystalline form existed in the polyaniline nanofibers and that the crystallinity of polyaniline increased with decreasing diameter of polyaniline nanofibers. The ESR spectra revealed the fact that the decrease in the intensity of the ESR signal was accompanied by the increase in the value of the peak-to-peak line width Delta H pp as the diameter of polyaniline nanofibers decreased. The (1)H NMR spectra showed that a peak in a triplet caused by the +/- NH free radical was split into two peaks with different intensities and that their relative intensity also changed with the diameter of the polyaniline nanofibers.     

PET／PA66／液晶共聚酯酰胺共混体系的流变性能

采用ＳＥＭ１、热偏光显微研究了聚对苯二甲乙二酯（ＰＥＴ）／聚酰胺６６（ＰＡ６６）／热致液晶共聚酯酰胺（ＬＣ３０）三元共混物的形态结构;利用Ｉｎｓｔｒｏｎ３２１１型毛细管流变仪研究了共混物的流变性能,结果表明：ＰＥＴ／ＰＡ６６／ＬＣ３０共混物为一热力学不相容的多相聚合物体系,ＬＣ３０的加入提高了ＰＥＴ／ＰＡ６６的相容性,有效地改善了ＰＥＴ／ＰＡ６６共混物的流变性能,ＰＥＴ／ＰＡ６６／ＬＣ３０三元共混     

Preparation and rheological characterization of poly(n-butyl methacrylate)/montmorillonite composites

Intercalated nanocomposites constituted of poly(butyl methacrylate) (PBMA) as the matrix and an organically modified montmorillonite as the nanosize filler were prepared and rheologically characterized in detail. The rheological behavior of the composites showed dependence on both temperature and clay content. For composites of low clay contents, the steady shear viscosity showed a Newtonian plateau in the low shear rate region at low temperatures and the plateau was replaced by a shear-thinning curve when the temperature was raised. For composites of higher clay contents, strong shear-thinning behavior were observed at all shear rates and all temperatures. The viscoelastic data of the composites showed unusual terminal behavior of a decreasing terminal slope at low frequencies with increasing temperature and clay loading. X-ray diffraction spectra showed that annealing process at higher temperatures shifted the Bragg reflection peaks to a lower angle and broadened the peaks, which provided the evidence for the existence of a temperature-induced solid-like structure that was responsible for the shear thinning and the unusual terminal viscoelastic behavior.     

Viscoelastic and shear viscosity studies of colloidal silica particles dispersed in monoethylene glycol (MEG), diethylene glycol (DEG), and dodecane stabilized by dodecyl hexaethylene glycol monoether (C12E6)

Silica dispersions stabilized by a nonionic surfactant, dodecyl hexaethylene glycol monoether (C 12E 6), were studied using rheological measurements. The viscosity-shear rate flow behavior of silica in monoethylene glycol (MEG) is shear thinning at low shear rates, leading to a Newtonian plateau at high shear rates for all dispersions studied. All rheological properties showed an increase above a critical surfactant concentration. The dispersions were stable at low levels of C 12E 6 concentrations because of electrostatic repulsions as deduced from the zeta potentials of silica that were on the order of about -30 to -65 mV in monoethylene glycol (MEG). Instability on further addition of C 12E 6 to the silica particles, a phenomenon normally obtained with high-molecular-weight polymers, was observed in MEG. Viscoelatic measurements of silica in monoethylene glycol at various surfactant concentrations showed a predominantly viscous response at low frequency and a predominantly elastic response at high frequencies, indicative of weak flocculation. Instability is explained in terms of hydrophobic and bridging interactions. Restabilization observed at high surfactant concentration was due to the steric repulsion of ethoxy groups of micellar aggregates adsorbed on silica particles. The study also revealed that the presence of trace water introduced charge repulsion that moderated rheological measurements in glycol media and introduced the charge reversal of silica particles in dodecane.     

Correlation of the Dielectric Properties of Dispersed Particles with the Electrorheological Effect

The dc field rheological properties and frequency dependent dielectric properties of a set of electrorheological (ER) fluids composed of oxidized polyacrylonitrile or aluminosilicate materials dispersed in silicone oil were examined in this paper. Our experimental investigations show that there is a complicated relationship between the dielectric properties of dispersed particles and the ER effect. The dielectric loss of dispersed particles, which has not attracted much attention in previous work, was found to play a considerable role in ER response. The large dielectric loss tangent, experimentally around 0.10 at 1000 Hz, is found to be needed for a strong ER effect. A good ER solid material should first have large dielectric loss, and then the higher the dielectric constant, the stronger the ER effect. The large dielectric loss would facilitate the turning of dispersed particles, and the high dielectric constant would maintain the fibrillation structure stable and strong. Two processes, the particle turning process and the particle polarization process, are thought to be involved in ER activity. Our findings, in connection with the Wagner model, can better explain why the strongest ER effect occurs at particle conductivity of 10⁻⁷S/m; why the shear stress of some ER fluids decreases with frequency while with others the shear stress increases with frequency; and why trace water can enhance the ER effect considerably, which would help in understanding the mechanism of the ER effect. Too large a dielectric loss is thought to be unfavorable for the ER effect, and its suitable range is worth further study. The results also present a method of designing high performance ER fluids, which would significantly promote development of electrorheology and its application in industrial areas.     

In situ sol-gel preparation of polysaccharide/titanium oxide hybrid colloids and their electrorheological effect

A new type of organic/inorganic hybrid colloid, made of modified carboxylmethyl starch (CMS) and titanium oxide (TiO(2)), was synthesized by an in situ sol-gel technique. IR spectra analysis shows strong a interaction of functional groups between two components, whose dispersion is almost at the molecular level. Due to the highly active surfaces hybrid particles and their characteristic dielectric behavior in accordance with the previous theoretic calculation, the suspensions of hybrids in silicone oil display a remarkable ER effect. The static yield stress can be above 20 kPa (shear rate 5 S(-1)) under a direct current field of 4 kV/mm at room temperature, much higher than that of simple blends of starch and titanium dioxide. In the meanwhile, the temperature dependence and sedimentation stability were optimized. Based on existing experimental results, we propose that dielectric properties and surface (interface) activity are two necessary conditions fulfilling the requirement of high ER activity. The combination of both factors may effectively reduce the activation energy needed for ERF restructuring.     

Rheological Properties of Silica Particle Suspensions in Mineral Oil

The rheological properties of particles suspended in a non‐polar mineral oil have been investigated as a function of volume fraction of particles, particle size, surface properties and shear rate. Three different types of particles were investigated; glass microspheres, monodisperse silica particles and fumed silica. The suspensions showed shear thinning behavior at higher volume fractions, and the viscosity increased with decreasing particle size. The hydrophobic particles display lass shear thinning effects. The relative viscosity of all the suspensions was well fitted to the Krieger and Dougherty model.     

Rheodielectric spectroscopy on heterogeneous polymer systems —electrorheological fluids

The technique of rheodielectric spectroscopy is used to investigate the dielectric behaviour of electrorheological fluids (ERF) as a function of external electrical DC-field and/or shear rate. Commercial ERF's consisting of mesoscopic polyurethane particles in a silicone oil matrix were studied. The particles contain a salt which leads to strong dipole moments via the Maxwell-Wagner-Polarization (MWP) if subjected to an external electrical field. In an electrical field the dipoles and, concomittantly, the particles motion become correlated leading to the formation of solid-like structures and significant changes in the viscosity. We demonstrate that dielectric spectroscopy is capable of monitoring the field and shear rate effects in terms of relaxation strength and relaxation time of the MWP. In electrical or shear fields dipole-dipole correlations increase the MWP's relaxation strength, so that we are able to observe structure formation with dielectric spectroscopy, especially the time resolved response of the ERF to changes in the electrical field or the shear rate.