Abstract: The synthesis of protein-silver ultrafine particles by inverted microemulsion method and the preparation of ER fluid of these particles dispersing in insulating oil are reported.Several parameters of the ER fluid are studied including the structure,stability,static yield stress (τ_s) and the leakage cur rent density (J).Factors which affect the above parameters are discussed.The ER fluid of protein-silver shows high yield stress and low leakage current even in weak electric field (E),and J^∝aE^b.

Key words: electrorheological fluid, bovine serum albumin, hemoglobin, ultrafine particle, silver, microemulsion