Abstract: A magnetorheological (MR) piston assembly includes an MR piston, a rod, and a guide member. The guide member includes an MR fluid passageway and is attached to at least one of the piston and rod. A perimeter of a projection of the guide member onto a plane perpendicular to the longitudinal axis surrounds and is spaced apart from a perimeter of a projection of the MR piston onto the plane A damper includes an MR piston assembly and a tube. The piston assembly includes a piston, a rod, and a guide member. The guide member includes an MR fluid passageway and is attached to at least one of the piston and rod. The guide member diameter is greater than the piston diameter. The tube surrounds and is radially spaced apart from the piston and surrounds the guide member, wherein the guide member makes sliding contact with the tube.

Abstract: Hydrophobic metal particles that are useful as the magnetizable particles in magnetorheological fluids and magnetorheological elastomers are provided. Hydrophilic metal particles, such as carbonyl iron particles, are made hydrophobic by reacting a surface hydroxyl on the solid metal particle with a reactive surfactant. Particles are coated with the reactive surfactant to cover at least about 90% of the surface of the particles and then washed with a low viscosity synthetic hydrocarbon to remove any excess surfactant. The particles are stabilized against oxidation and irreversible coagulation during further processing, and formulation and use in magnetorheological fluids and elastomers.