CHARACTERISTICS OF ELECTRORHEOLOGICAL RESPONSES IN AN EMULSION SYSTEM

The characteristics of electrorheological (ER) responses in an emulsio n system have been examined for the first time. The emulsion system co nsists of a chlorinated paraffin oil and a silicone oil; these two liq uids have similar dielectric constants, but the former liquid is 1000 times more conductive than the latter liquid. The mismatch in electric properties between the dispersed phase and the dispersing medium can be reversed in an emulsion by inverting the phase distribution. Transi ent ER responses in the emulsion system have been studied over a range of shear rates following step changes (on/off) of an external de elec tric field. The relative response strength characterizing the ER effec t increases with the field strength and with the volume fraction of si licone oil, but decreases with increasing shear rate imposed. The para ffin oil-in-silicone oil emulsion exhibits a response much stronger th an that observed in the phase-reversed silicone oil-in-paraffin oil em ulsion. No negative ER response is detected in the silicone oil-in-par affin oil emulsion. With an optical microscope, very different microsc opic response characteristics are observed for the phase-reversed emul sions under static conditions, and this can be explained according to the leaky dielectric liquid model of Taylor. (C) 1997 Academic Press.