Electrorheological Effects of ER Gels Containing Iron Particles

Electrorheological (ER) gels were prepared by aligning 5-mm iron particles in liquid-like silicone RTV prepolymers in magnetic fields while the silicone cured. The pre-cured composite was then swollen with oil to reduce the conductivity. The iron content was held at 3% by volume, while the oil content ranged up to 20% by weight. In general, the dynamic shear moduli of the aligned ER gels increased quadratically with the electric field intensity, following the empirical equation G = G 0 [1 + (E/E 0 ) α ], with α≈ 2. Observed values of G/G 0 ranged up to 2.5. When the iron-particle chains were tilted with respect to the electrical field direction, the electrorheological effect decreased. While the rate of decrease was in approximate accord with the prediction of the point-dipole assumption, the magnitudes of the ER effect were under predicted by two orders of magnitude.