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Using three different carbonaceous particles, we investigated the electrical and rheological properties of several ER fluids. Each of the carbonaceous particles, prepared from different treatment methods, possesses a different oxygen content or degree of crystallinity. These materials were prepared from mesophase pitch and were cationically polymerized with naphthalene and HF/BF[sub 3] at high temperature (500∼700°C). Special focus was placed on the variables affecting ER properties, including current density, temperature, electric field strength, and volume fraction of the particles. Rheological properties were measured by a rotational rheometer equipped with a high voltage generator. To investigate the durability of the carbonaceous ER fluids, we also measured changes in shear stress, shear viscosity, and current density at the shear rate of 50 sec[sup -1] and different temperatures (from 20 to 100°C). Good thermal and electrical stability of the carbonaceous particlebased ER suspensions were observed. [ABSTRACT FROM AUTHOR]

Copolyanilines are synthesized by a chemical oxidation of aniline and o-ethoxyaniline with various molar ratios in an acidic media, and then characteristics of these polymers such as chemical structure, particle size and the particle size distribution were examined by using FT-IR, SEM and particle size analyzer, respectively. Suspensions of copolyaniline containing ethoxy group, namely poly(aniline-co-oethoxyaniline), in silicone oil have been investigated as one of many potential candidates for dry-base electrorheological (ER) fluid systems. Rotational rheometer (Physica) equipped with a high voltage generator was used to characterize the rheological properties of ER fluids from both steady shear and dynamic tests. From the steady shear experiment, we obtained flow properties and found that ER fluids exhibited the yield phenomenon. On the other hand, viscoelastic property was also obtained from the dynamic experiment. Since viscoelastic properties for ER fluids are mainly dominated by the particle chain structure, the state at different time scale was analyzed from the rheological parameters such as storage modulus (G'), loss modulus (G") and tanδ We conducted a strain amplitude sweep at 1Hz under an applied electric field to determine a linear viscoelastic region first. The G' and G" were then measured by a frequency sweep from 0.1 to 100 Hz in the linear viscoelastic region. [ABSTRACT FROM AUTHOR]

We report our experimental results on the electrorheological (ER) characteristics of ER fluids consisting of suspensions of semiconducting polyaniline and copolyaniline particles in silicone oil. Ionic sodium diphenylamine sulfonate and nonionic o-ethoxyaniline were introduced to synthesize copolyanilines, i.e. N-substituted copolyaniline and poly (aniline-co-o-ethoxyaniline), respectively. ER fluids using these particles were compared. ER fluids, which contain the ionic copolymer, showed the highest ER performance among polyaniline and its copolymer systems. This result was interpreted in terms of the conductivities of the particles and their dielectric spectra. [ABSTRACT FROM AUTHOR]

Polyaniline-Na[sup +]-montmorillonite nanocomposite particles were synthesized using an emulsion intercalation method, and electrorheological (ER) fluids were produced by dispersing the synthesized nanocomposite particles in an electrically-insulating silicone oil. The emulsion of an aniline monomer with dodecyl benzenesulfonic acid was inserted into the layers of clay, and polymerization was processed by adding the oxidant initiator solution. DBSA as a emulsifier and a dopant took a important role for polyaniline clay nanocomposite. This insertion of polyaniline was confirmed by Xray diffraction. To observe its ER properties, we measured the shear viscosity and the shear stress by controlling shear rate. Furthermore, we conducted dynamic tests to investigate the viscoelastic properties of the ER fluid under an electric field in the linear viscoelastic region. [ABSTRACT FROM AUTHOR]