Synthesis and electrorheological properties of polyaniline-Na+-montmorillonite suspensions

We synthesized polyaniline-Na⁺-montmorillonite nanocomposite particles using an emulsion intercalation method and prepared electrorheological (ER) fluids by dispersing the synthesized nanocomposite particles in an electrically insulating silicone oil. The conducting polymer (polyaniline) was inserted into the layers of clay, and this insertion of polyaniline was confirmed by X-ray diffraction. For the first time, ER properties were determined via a rotational rheometer equipped with a high voltage generator.     

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     

New Approach to Enhance the Yield Stress of Electro‐Rheological Fluids by Polyaniline‐Coated Layered Silicate Nanocomposites

We synthesized new polyaniline (PANI)/organoclay (aminosilane surface‐treated) nanocomposite particles and prepared electro‐rheological (ER) fluids by dispersing the particles in silicone oil. A distinct enhancement in yield stress was observed due to the presence of PANI‐coated clay particles. The effects of delaminated clay on the ER yield stress were investigated and compared with other ER fluid systems, which use PANI particles only or a simply intercalated PANI/clay nanocomposite.     

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.     

Electrorheological characterization of polyaniline-coated poly(methyl methacrylate) suspensions

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.     

Effect of ionic pendent groups on a polyaniline-based electrorheological fluid

Particles of semiconducting polyaniline and a copolyaniline bearing ionic substituents were synthesized. Electrorheological (ER) fluids using these particles were compared with each other with respect to their rheological properties and dielectric spectra. In the steady shear rheological experiment conducted at 3 kV/mm (DC) at 25°C, the copolymer system showed higher stress than the polyaniline system in the whole shear rate region. This result was interpreted in terms of the conductivities of the particles and their dielectric spectra. Especially, the different behavior in the high shear rate region can be related to the electrical relaxation phenomena observed in the dielectric spectra.     

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     

用共混和共聚法改性聚苯胺及其电流变液的研究

通过共混和表面接枝共聚两种方法改性聚苯胺，制备聚苯胺（ＰＡｎ）复合粒子并用它们组成活性较高的电流变（ＥＲ）液．研究了ＰＡｎ复合粒子的结构与ＥＲ液性能的关系．结果表明在ＰＡｎ粒子表面涂覆聚乙烯醇或接枝聚丙烯酰胺等与ＰＡｎ能形成氢键或有化学键连接的绝缘物质可以既提高其ＥＲ液的电诱导屈服应力又降低漏电流密度．     

Electrorheological properties of suspensions of monodispersed micron‐sized polyaniline composite particles

Monodispersed micron‐sized polyaniline (PANi) composite particles were synthesized by chemically oxidative polymerization of aniline in the presence of functional porous polymer particles. The formation of the PANi‐coated composite particles was confirmed by scanning electron microscopy. Electrorheological (ER) properties of the monosized composite particle suspensions were then investigated under different DC electric fields by altering the particle characteristics. The ER effect of the PANi composite suspensions was largely dependent on the composition ratio (PANi loading), the particle conductivity, and the particle concentration. Dynamic oscillation measurements revealed that the applied electric field induced the viscoelastic property of the ER suspensions by generating the chain structures of the suspended particles. © 2002 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 40: 1163–1170, 2002     

Polyaniline and its modification for electroresponsive material under applied electric fields

Polyaniline (PANI) and its various copolymers were synthesized using different monomers such as o‐methyl‐, o‐methoxy‐, o‐ethyl‐, o‐ethoxyaniline and sodium diphenylamine sulfonate by the chemical oxidation polymerization as air‐stable organic conducting polymers, and adopted as one of the most potential materials of electrorheological (ER) fluids, especially for the anhydrous system. A relatively low density, a controllable conductivity, and thermal stability are advantages of the PANI based ER system compared with other ER materials. An FT‐IR analysis was adopted to confirm their synthesis and a scanning electron microscopy (SEM) analysis indicated the shape of PANI derivatives was irregular. The effect of functional group of PANI on electric and electroresponsive properties of poly(aniline‐co‐ethoxyaniline) (COPA) particles were examined. A universal scaling equation of the yield stress was applied to these ER fluids and it was found that all data were collapsed successfully onto a single curve regardless of monomer type of the polyaniline synthesized. Copyright © 2005 John Wiley & Sons, Ltd.     

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.     

核壳型聚苯胺/钛酸钡的结构及其电流变性能

用改进的溶胶-凝胶法制备了核壳型聚苯胺/钛酸钡复合微粉,通过TEM及FT-IR分析表征了其形貌及微观结构,用复合微粉与氯化石蜡油配制成无水电流变(ER)液,研究其不同膜厚核壳粒子的电流变性能.研究结果表明,聚苯胺/钛酸钡复合粒子配置成的电流变液的电流变性能较纯聚苯胺的为强;钛酸钡的涂层厚度对复合粒子电流变性能有重要影响;并在d=20 nm时获得最佳电流变性能.     

Electrorheological behavior of copper phthalocyanine-doped MCM-41 suspensions

A type of anhydrous electrorheological (ER) material of copper phthalocyanine (CuPC)-doped MCM-41 was synthesized by in situ micelle-assisted incorporation of CuPC during MCM-41 synthesis. The ER behavior of the suspensions of CuPC-doped MCM-41 particles in paraffin liquid with a 30 wt.% was investigated under an applied electric field. It is found that the ER effect increased with increasing the CuPC-doping ratio. The dopants of CuPC molecules within the mesochannel of MCM-41 mesoporous sieve improved the conductivity of the particles, and produced a proper conductivity of 10⁻⁷ S m⁻¹. Dielectric spectra of the fluids were also measured to examine their possible correlation with the ER behavior, and the results were explained based on Ikazaki's criterion that the relaxation frequency must be in the range 100–10⁵ Hz and the difference in the dielectric constant must be large below and above the relaxation frequency for an appreciable ER effect.     

Synthesis and Characterization of Polyaniline/Mesoporous SBA‐15 Nanocomposite

Mesoporous silica SBA‐15 with conducting polyaniline inside the pore channels was synthesized and nanocomposite formation was confirmed by means of X‐ray diffraction, transmission electron microscopy and via an N₂ adsorption isotherm. The nanocomposite was subsequently used as a dispersed phase in electrorheological (ER) fluids, and the ER effect has been demonstrated for the first time using a rotational rheometer with high voltage generator.     

Electrorheological fluid characterization via a vertical oscillation rheometer

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.     

Monodisperse conducting colloidal dipoles with symmetric dimer structure for enhancing electrorheology properties

This study introduces an electrorheological (ER) approach that allows us to obtain remarkably enhanced ER properties by using monodisperse colloidal dimer particles. Two sets of colloidal particles, which are spheres and symmetric dimers, were synthesized employing the seeded polymerization technique. The aspect ratio of dimer particles was ~1.43. Then, the surface of the particles was coated with polyaniline by using the chemically oxidative polymerization method. After preparation of the particle suspensions having the same particle volume and concentration, their ER behavior was investigated with changing the electric field strength. At the same experimental condition, both shear stress and shear yield stress of the dimer particle suspension remarkably increased, compared with those of the spherical particle suspension. This attributes to the fact that the shape anisotropy of suspending particles effectively led to increase in the dipole moment under the electric field, thus resulting in formation of a well-structured colloidal chains between the electrodes.     

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.     

含双噻唑基聚合物的合成及电流变性能研究

采用2，2’-二氨基-4，4’-双噻唑与联苯胺合成一种含有双噻唑基的共轭聚合物，通过红外、扫描电镜、热重分析等测试了该物质的结构及热稳定性等，并通过将聚合物分别分散在硅油和溴代二苯甲烷中制备电流变体，测试其电流变性能。结果表明：含双噻唑基的共轭聚合物作为电流变体的分散相表现出了良好的电流变性能，同时发现分散相和分散介质的密度相近时有利于电流变性能的提高。     

Polarization processes in electrorheological fluids based on conductive polymers

Electrorheological (ER) fluids are composed of dielectric particles dispersed in an inert liquid of low electric permittivity. Upon the application of an electric field ER fluids rapidly solidify, or increase their viscosity. Characteristic increase of the viscosity of ER fluids is due to the formation of particle chains that bridge the electrodes. This process is greatly affected by polarization processes within the solid phase and at the surface of the grains. These phenomena are governed by dopants, functional groups, structure of the solid particles and the solid/liquid interface. To find relations between parameters of the ER effect and material properties of components of ER fluids, two main types of the materials were investigated: conjugated polymers [polyphenylene (PPP), pyrolyzed polyacrylonitrile (PAN) and polythiophene] and solid electrolytes based on polyacrylonitrile complexed with inorganic salts. It was found that the ER activity resulted from surface polarization processes due to the presence of polar species (PAN) or bulk polarization related to mobile ions (PPP). Polythiophene, despite the presence of a conjugated system of multiple bonds, showed only residual ER effect. Solid electrolyte‐based fluids exhibited relatively high activity originated from ionic polarization. Copyright © 2006 John Wiley & Sons, Ltd.     

pH- and thermosensitive polyaniline colloidal particles prepared by enzymatic polymerization

Polyaniline colloids were prepared by enzymatic polymerization using chitosan and poly(N-isopropylacrylamide) as steric stabilizers. The resulting nanoparticles undergo flocculation by changing the pH or temperature of the aqueous dispersions. The environmentally responsive behavior of these colloids contrasts with that of polyaniline colloids synthesized using poly(vinyl alcohol) as the steric stabilizer. The colloid size was a function of the steric stabilizers and ranged from approximately 50 nm for polyaniline particles prepared in the presence of chitosan and partially hydrolyzed poly(vinyl alcohol) up to 350 nm for the particles synthesized using poly(N-isopropylacrylamide). UV-visible and Fourier transform infrared spectroscopic studies indicate that polyaniline colloids are spectroscopically similar to those obtained by traditional dispersion polymerization of aniline by chemical oxidation. These polyaniline colloids have potential applications in thermochromic windows and smart fluids.