Electrorheology of silicone oil suspensions of urea-modified poly[(glycidyl methacrylate)-co-(ethylene dimethacrylate)] particles

Two methods of modification of poly[(glycidyl methacrylate)-co-(ethylene dimethacrylate)] microspheres with urea were examined in this electrorheological (ER) study. First, the urea functional groups were introduced by chemical modification of the starting copolymer. A significant increase in storage modulus of the silicone oil suspension was observed compared with the loss modulus when an electric field is applied. On the other hand, the ER effect in suspension of particles coated with physically bonded urea was only slightly higher than that of untreated material. This is explained by poor coating of the hydrophobic microparticle surface with hydrophilic urea. According to dielectric measurements, the interfacial polarization was found to be responsible for the formation of chain structure of modified microspheres in the electric field resulting in the ER effect.