Measurement of interaction forces at small distance under electric field in a smectite dispersed silicone oil based ER fluid

The apparatus to measure interaction forces under an electric field at smal l distance between a conductive hemisphere and a flat plate has been develo ped. The surface forces at small distance sandwiched ER fluid dispersing ul trafine smectite particles (20 to 50 nm thickness) in silicons oil has been measured. This fluid shows 0.7kPa of apparent yield stress by applying 2.5 kV/mm of DC electric held. When an electric field applies to this ER fluid. the repulsive energy curves shows inflection points at about 0.2 mum dista nce periodically at small distance of less than 1 mu m because the repulsio n force? decreases for a vacancy of particles after the particles are pushe d out and the dipole attraction force acts: between hemisphere and plate. O n the other hand. when the electric field becomes off and it passes enough time, the inflection points is observed more shorter distance of about 0.15 mu m periodically. The coagulated particle size is estimated about 0.15 mu m under no electric field and becomes larger by applying electric field.