Experimental and theoretical study of the field induced phase separation in electro- and magnetorheological suspensions

We present here the study of field induced phase separation in E.R. and M.R . fluids. Two thermodynamic models - one for the formation of chains of par ticles and the other for phase separation are presented and compared with e xperimental results obtained with two kinds of suspensions. One was made of silica particles in silicone oil and the other was made of magnetic polyst yrene particles in water. In the presence of a flow the phase separation oc curs with the dense phase forming a regular pattern of stripes. The depende nce of the period of these stripes on the intensity of the magnetic field i s well reproduced by the same kind of thermodynamic model if we add the eff ect of normal stresses induced by the shear flow.