TRANSIENT-RESPONSE OF ELECTRORHEOLOGICAL EFFECT TO A STEP FIELD IN ANIMMISCIBLE POLYMER BLEND - FIRST MODE IN TYPE-I BLEND

We have investigated the initial transient response of an immiscible p olymer blend electrorheological fluid to a step electric field by mean s of microscopic observations and measurements of the transmitted ligh t intensity and the shear stress. In the absence of shear flow, the tr ansmitted light intensity increased steeply in the early stage after a pplying a step field, corresponding to the elongation and coalescence of droplets of one polymer dispersed in the other to form bridges alon g the field. In the presence of shear flow, on the other hand, the inc rease of transmitted light intensity was followed by that of shear str ess. From this fact it was clarified that the stretched structure cons isting of elongated droplets and bridges tilt from the direction of th e field in addition to the elongation under shear flow, and the electr orheological effect in the early stage should be ascribed to the forma tion of elongated structures followed by the tilt of them. (C) 1998 Th e Society of Rheology.