The spherical, monodisperse polymer microshperes (PAPMMAs) consisting of a poly(methyl methacrylate) (PMMA) core and a polyaniline (PANI) shell were prepared and adopted as dispersed materials for electrorheological (ER) fluids, in which electrical conductivity was originated primarily from the surface-coated conducting PANI layer. These surfaces were rough and irregular. Three different core sizes of PAPMMAs (2, 4.5, and 9 μm) with the same weight ratio of PANI, the larger core having the thicker PANI shell, were prepared. PAPMMAs that have similar shell thicknesses but different core sizes were also prepared in order to examine the particle size effect on ER performance. Performances of PAPMMA-based ER fluids were enhanced with increasing core particle size. The same result was obtained for the PAPMMA systems having the same shell thickness. Dielectric spectra of these ER fluids were found to provide additional information on both analyzing their electrical polarization properties and interpreting the flow behavior of the PAPMMA-based ER fluids.

A composite material of a silica-based mesoporous molecular sieve, MCM-41, with conducting polyaniline (PANI) inside the uniformly aligned one-dimensional channels (PANI/MCM-41) was prepared and its nanocomposite formation was confirmed through an electrical conductivity measurement. This nanocomposite particle was adopted for a dispersed phase in electrorheological (ER) fluids, and the ER property was measured using a Couette-type rotational rheometer equipped with a high voltage generator. Suspension of PANI/MCM-41 showed ER properties more enhanced than those of MCM-41 or PANI alone as a result of the anisotropic polarization of the PANI/MCM-41 nanocomposite.

The yield stress dependence on electric field strength for electrorheological (ER) fluids is examined. A proposed scaling function incorporates both the polarization and conductivity models. Proper scaling allows yield stress data for ER fluids to collapse onto a single curve for a broad range of electric field strengths.

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