FALLING BALL EXPERIMENTS IN A DILUTE ELECTRORHEOLOGICAL FLUID

The velocity v of a glass ball falling through a dilute electrorheolog ical fluid of silica gel particles in oil is measured as a function of applied electric field E for various particle sizes and concentration s. The fields used range up to the point where the ball ceases to fall . The results are consistent with a model using two types of field-dep endent retarding force, one proportional to E(2) and the other proport ional to vE(2). The latter is proportional to both particle size and p article volume fraction, while the former is independent of particle s ize and is significant only above a volume fraction co where it is pro portional to c-c(0). The force in E(2) is related to the yield stress and is attributed to chain breaking by the ball. The force in vE(2) is attributed to transient chain deformations when the ball impacts chai ns.