Fluid responsive to a magnetic field

DETAILED DESCRIPTION The present invention is a rheological fluid which is responsive to a magnetic field.
The fluid consists essentially of a vehicle; magnetizable particles suspended in the vehicle; and a dispersant.
The dispersant comprises an amount of small, non-magnetizable, dispersant particles which are insoluble in the vehicle.
The dispersant particles have no dimension greater than 10 nanometers.
The dispersant particles are capable of reversibly bonding to the magnetizable particles by Van der Waals forces.
The amount of dispersant particles is an effective amount to provide a thin coating of dispersant particles on the surface of each of the magnetizable particles.
The coating prevents the magnetizable particles from directly contacting each other during application of magnetic fields and forming particle agglomerates in the absence of a magnetic field.
For purposes of the present application, the term "reversibly bonding" means that the dispersant particles are neither electrostatically bonded to the surface of the magnetizable particles, nor fused to the surface of the magnetizable particles.
The dispersant particles are readily displaced on and away from the surface of the magnetizable particles.
An effective amount of dispersant particles is about 0.
1-20 volume percent based on the volume of the magnetizable particles, preferably about 1-7 percent.
Preferably, the vehicle is present in an effective amount to wet the surfaces of the magnetizable particles and the dispersant particles and to fill the voids between the magnetizable particles.
Broadly, the amount of vehicle can be about 10-100 volume percent based on the combined volume of dispersant plus magnetizable particles.
A preferred amount is about 25-65 volume percent based on the volume of the dry mixture of dispersant plus magnetizable particles.
The present invention also resides in a clutch, shock absorber, and other such device comprising the rheological fluid of the present invention.
Advantages of the rheological fluid of the present invention are that the fluid exhibits good stick-slip behavior