Preparation and electrorheological characterization of suspensions of monodisperse micron-sized styrene-acrylonitrile copolymer particles

Monodisperse micron-sized styrene-acrylonitrile copolymer (SAN) particles were prepared by a seeded swelling and polymerization method. Polystyrene particles prepared by dispersion polymerization were used as the seed latex. Characteristics of the particles were examined by scanning electron microscopy, FT-IR spectroscopy, H-1 NMR spectroscopy, thermogravimetric analysis and dielectric analysis, then the electrorheological (ER) behavior of the particle suspensions in silicone oil was investigated. The polarization ability of particles represented by the particle dipole coefficient increased greatly with the degree of hydrolysis of the nitrile component of SAN particles. As the acrylonitrile content of the copolymer particles was increased, the hydrolyzed particles exhibited higher dipole coefficients and, consequently, increased ER properties. Also, the effect of particle size on ER properties was studied by varying the size of these monodisperse copolymer particles.