TOWARDS UNDERSTANDING ER FLUIDS USING SALS/RHEOMETRY
This paper details work in Cranfield and Leeds Universities of making a stock of transparent ER fluids, which could later be utilised in a new optical electro rheometer (OER) to be assembled at Leeds University. Two basic routes were attempted. One was to use glass microspheres and the other was to use polymer spheres. In order to increase the strength of the ER effect, it was necessary to increase the volume loading while still maintaining sufficient transmission (about 75% over 2 mm). It was found to be possible to increase the ER effect quite substantially in some instances, and in others it was possible to get a near perfect refractive index match. It was not possible to combine both requirements in one fluid such that a high static yield stress was apparent in a transparent ER fluid. However one fluid was made which gave acceptable diffraction losses at high volume fractions, remained in suspension for extended periods and provide about 700 Pa yield stress at 4kV/mm and about 30% volume fraction viz: untreated poly(ethylene vinyl acetate) microspheres in Cereclor/bromonaphthalene/polystyrene solution. The OER being assembled at Leeds University is intended to record small angle light scattering (SALS) profiles, electrical and mechanical properties of ER fluids simultaneously. The OER is based around a DSR 500 machine purchased from Rheometric Scientific with quartz tools coated with transparent indium tin oxide(ITO), which is capable of measuring both steady state (DC) and oscillatory (AC) material parameters.