Electrorheology of filled silicone elastomers

Electrorheological (ER) silicone elastomers containing particles based on s ilica (SiO2) and titania minerals (BaTiO3, Ba2Ti9O20, and BaTiO3/CaZrO3) we re prepared and characterized. An electrical field was applied to align the particles during the cure of the silicone prepolymer. For the: silicone/si lica compositions, a prominent Maxwell-Wagner dispersion in the dielectric response suggested that surface conductivity of the silica particles domina ted the polarization. Alignment of the particles increased the overall diel ectric permittivity as well as the magnitude of the Maxwell-Wagner dispersi on. Their ER response exhibited a negative deviation ft om a quadratic depe ndence on field intensity at high fields, and was accompanied by nonlinear conductivity. A highly nonlinear enhancement of the ER effect with increasi ng particle concentration was observed. For the silicone/titania elastomers as a class, the ER response increased with the particle's permittivity. In the case of the silicone/BaTiO3 elastomer, the ER effect increased with he ld frequency, as expected from high permittivity of BaTiO3 relative to sili cone, whereas the opposite dependence was observed fur the silicone/silica ER elastomer, suggesting a conduction polarization mechanism for the latter . (C) 2001 The Society of Rheology.