Low viscosity, electrically conductive ferrofluid composition and method of making and using same

Claim 2

In an electrically conductive ferrofluid composition, which composition comprises: (a) a polar liquid carrier; (b) finely divided magnetic particles dispersed in the polar liquid carrier and in an amount to provide magnetic properties to the ferrofluid composition; (c) a surfactant to disperse and stabilize the magnetic particles in the polar liquid carrier, the improvement of which comprises: (i) a polar-ionizing or dissociation agent which agent is miscible with the polar liquid carrier and which agent comprises an oxygen-containing agent selected from a group consisting of an alkylene polyol, an ether of an alkylene polyol or combinations thereof, the agent present in an amount sufficient to ionize or dissociate the surfactant and to provide a ferrofluid composition having an electrical resistivity of less than about1×10 7 ohms-centimeters.

Claim 3

The composition of claim 1 wherein surfactant comprises a cationic surfactant.

Claim 4

The composition of claim 2 wherein the cationic surfactant comprises a quaternary ammonium cationic surfactant having a long chain miscible in the liquid carrier.

Claim 5

The composition of claim 1 wherein the polar liquid carrier comprises a polyol ester or a polyalpha olefin.

Claim 6

The composition of claim 1, which composition includes an anionic surfactant as a first coating layer of surfactant on the magnetic particles and a second cationic surfactant as a second coating layer.

Claim 7

The composition of claim 5 wherein the cationic surfactant comprises a quaternary ammonium cationic surfactant.

Claim 8

The composition of claim 1 wherein the surfactant is present in a ratio by weight of surfactant to magnetic particles of from about 1:1 to 20:1.

Claim 9

The composition of claim 1 wherein the agent comprises a polyalkylene glycol polyether.

Claim 10

The composition of claim 8 wherein the agent comprises a di-, tri- or tetraethylene glycol alkyl ether.

Claim 11

The composition of claim 1 wherein surfactant is present in an amount in excess of the amount sufficient to disperse and stabilize the magnetic particles.

Claim 12

The composition of claim 1 wherein the agent is selected from the group consisting of: diethyl glycol dibutyl ether; tetraethylene glycol dimethyl ether; triethylene glycol dimethyl ether; diethylene glycol diethyl ether; diethylene glycol dimethyl ether; ethylene glycol diethyl ether; polyethylene glycol and polypropylene glycol.

Claim 13

The composition of claim 1 wherein the magnetic particles comprise ferromagnetic particles having a diameter ranging from about 20 to 200 angstroms.

Claim 14

The composition of claim 1 wherein the composition includes carbon particles dispersed in the ferrofluid composition.

Claim 15

The composition of claim 13 wherein the carbon particles are present in an amount of up to about 5 percent by weight of the ferrofluid composition.

Claim 16

The composition of claim 14 wherein the ferrofluid composition has a viscosity of less than about 200 cps at 25° C. and an electrical resistivity of less than about 1×10 6 ohms.

Claim 17

The composition of claim 13 which includes carbon particles having an average diameter of about 100 angstroms or less.

Claim 18

The composition of claim 1 wherein the surfactant comprises a first coating layer on the magnetic particles of a long chain fatty acid as a first anionic surfactant and a second coating layer of a quaternary ammonium alkoxy compound as a second surfactant.

Claim 19

The composition of claim 17 wherein the first surfactant is present in an amount of from about 5 to 10 percent by volume of the composition, and the second surfactant is present in an amount of from about 2 to 12 percent by volume.

Claim 20

The composition of claim 17 which includes from about 1 to 6 percent by volume of surfactant-coated carbon black particles.

Claim 21

The composition of claim 1 wherein the agent comprises from about 3 to 20 percent by volume of the composition.

Claim 22

The composition of claim 1 wherein the surfactant comprises a cationic surfactant selected from the group consisting of: quaternary imidazoline salts; aliphatic quaternary ammonium salts; and quaternary acylated polyamine salts.

Claim 23

In an electrically conductive ferrofluid composition, which composition comprises: (a) a polar liquid carrier; (b) finely divided ferromagnetic particles dispersed in the polar liquid carrier and in an amount to provide magnetic properties to the ferrofluid composition; and (c) a surfactant to disperse and stabilize the ferromagnetic particles in the polar liquid carrier, the improvement which comprises: (i) wherein the surfactant comprises a first coating layer of a first anionic surfactant in an amount of from about 5 to 10 percent by volume of the composition and a second coating layer of a second cationic surfactant in an amount of from about 2 to 12 percent by volume of the composition; and (ii) carbon particles dispersed in the composition in an amount of up to about 5 percent by weight of the composition; and (iii) an ionizing or dissociating agent in an amount of from about 3 to 20 percent by volume of the composition, the agent selected from the group consisting of: diethyl glycol dibutyl ether; tetraethylene glycol dimethyl ether; triethylene glycol dimethyl ether; diethylene glycol diethyl ether; diethylene glycol dimethyl ether; ethylene glycol diethyl ether; polyethylene glycol and polypropylene glycol.

Claim 24

In an electrically conductive ferrofluid composition, which composition comprises: (a) a polar liquid carrier; (b) finely divided ferromagnetic particles dispersed in the polar liquid carrier and in an amount to provide magnetic properties to the ferrofluid composition; and (c) a surfactant to disperse and stabilize the ferromagnetic particles in the polar liquid carrier, the improvement which comprises: (i) wherein the surfactant comprises a first coating layer of a first anionic surfactant in an amount of from about 5 to 10 percent by volume of the composition and a second coating layer of a second cationic surfactant in an amount of from about 2 to 12 percent by volume of the composition; and (ii) carbon particles dispersed in the composition in an amount of up to about 5 percent by weight of the composition; and (iii) an ionizing or dissociating agent in an amount of from about 3 to 20 percent by volume of the composition, the agent selected from the group consisting of: diethyl glycol dibutyl ether; tetraethylene glycol dimethyl ether; triethylene glycol dimethyl ether; diethylene glycol diethyl ether; diethylene glycol dimethyl ether; ethylene glycol diethyl ether; polyethylene glycol and polypropylene glycol.

Claim 25

The composition of claim 22 wherein the first anionic surfactant comprises fatty acid, and the second surfactant comprises a quaternary ammonium surfactant.