Electrorheological (ER) fluids with high ER activity were based on polyaniline (PAn) composite particles

which were prepared by surface modification of partially dedoped PAn particles using blending with poly (vinyl alcohol) (PVA)

poly (methyl methacrylate) (PMMA)

or polystyrene (PSt)

or graft copolymerization with acrylamide The effects of structure of PAn composite particles on properties of the PAn based ER fluid were studied.The results showed that the PAn based ER fluid might be improved significantly when PAn particles were coated by PVA or grafted by polyacrylamide at a certain value

while PMMA or PSt coating of PAn composite particles would cause both static yield stress and leak current density for the ER fluids to decrease.It was suggested that composite particles may improve ER performance when the composite particles with strong interaction between PAn and insulative coating were appropriately designed

for example

insulative coating forms hydrogen-bonding or chemical bonding with particles.