Electrorheology of polyaniline-coated silica particles in silicone oil

The electrorheology of silica particles coated with protonated polyaniline or polyaniline base in silicone oil has been studied. The behaviour of suspensions has been compared with those of bare silica particles and polyaniline base powder. For a 1 wt.% suspension of polyaniline base, the low-shear viscosity (at 7.69 s(-1)) increased more than 25 times in the presence of the electric field, while the upper-shear viscosity (623 s(-1)) approached this value in its absence. In suspensions of coated silica particles, the viscosity increase was much lower, only a little higher than in a suspension of dry silica particles. The electrorheological performance of these systems is discussed in connection with the polarization characteristics resulting from the frequency spectra of permittivity and dielectric loss of suspensions and from the particle dipole coefficient.