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 susp ensions has been compared with those of bare silica particles and polyanili ne 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 t he electric field, while the upper-shear viscosity (623 s(-1)) approached t his value in its absence. In suspensions of coated silica particles, the vi scosity increase was much lower, only a little higher than in a suspension of dry silica particles. The electrorheological performance of these system s is discussed in connection with the polarization characteristics resultin g from the frequency spectra of permittivity and dielectric loss of suspens ions and from the particle dipole coefficient.