Magnetorheological fluid with a fluorocarbon thickener

1. A durable magnetorheological fluid formulation comprising:

a carrier fluid,

magnetizable particles dispersed in the carrier fluid,

a conventional thixotropic agent below an efficacious amount, and

a fluorocarbon grease wherein said fluorocarbon grease is effective to limit settling of the magnetizable particles.

2. The formulation of claim 1 wherein the fluorocarbon grease comprises a fluorocarbon polymer and a base oil.

3. The formulation of claim 2 wherein the fluorocarbon polymer comprises polytetrafluoroethylene.

4. The formulation of claim 1 wherein said conventional thixotropic agent is selected from the group consisting of precipitated silica, fumed silica, an organoclay, a metal soap, a metal soap complex and mixtures thereof.

5. The formulation of claim 1 wherein the formulation is substantially free of said conventional thixotropic agent selected from the group consisting of precipitated silica, fumed silica, an organoclay, a metal soap, and a metal soap complex.

6. The formulation of claim 1 wherein the carrier fluid is selected from the group consisting of natural fatty oils, mineral oils, polyphenylethers, dibasic acid esters, neopentylpolyol esters, phosphate esters, synthetic cycloparaffins, synthetic paraffins, unsaturated hydrocarbon oils, monobasic acid esters, glycol esters, glycol ethers, silicate esters, silicon oils, silicon copolymers, synthetic hydrocarbons, perfluorinated polyethers and esters, halogenated hydrocarbons, and mixtures thereof.

7. The formulation of claim 1 wherein the carrier fluid includes about 50-90% by volume polyalphaolefin and about 10-50% by volume dioctyl sebacate.

8. The formulation of claim 1 wherein the fluorocarbon grease has an NLGI grade of between about 1 and 3.

9. The formulation of claim 1 further comprising at least one additive selected from the group consisting of an organomolybdenum complex, an organomolybdenum thiocarbamate, and an organothiocarbamate.

10. A durable magnetorheological fluid formulation comprising:

a carrier fluid,

magnetizable particles dispersed in the carrier fluid wherein the magnetizable particles comprise water atomized iron powder,

a conventional thixotropic agent below an efficacious amount, and

a fluorocarbon grease wherein said fluorocarbon grease has an NLGI grade of between 1 and 3 and is effective to limit settling of the magnetizable particles.

11. The formulation of claim 10 wherein the carrier fluid comprises a polyalphaolefin and diotyle sebacate.

12. The formulation of claim 10 wherein the magnetizable particles comprise at least 50% water atomized iron powder.

13. The formulation of claim 10 wherein the fluid formulation further comprises an overbased sulfonate additive.

14. The formulation of claim 13 wherein the overbased sulfonate additive is present in an amount of from about 10 to 30 grams per liter based on total volume of the magnetorheological fluid formulation.

15. The formulation of claim 11 wherein the carrier fluid comprises about 50-90% by volume polyalphaolefin and about 10-50% by volume dioctyl sebacate.

16. The formulation of claim 10 wherein the fluorocarbon grease comprises polytetrafluoroethylene.

17. The formulation of claim 10 wherein said conventional thixotropic agent is selected from the group consisting of precipitated silica, fumed silica, an organoclay, a metal soap, a metal soap complex and mixtures thereof.

18. The formulation of claim 10 wherein the formulation is substantially free of said conventional thixotropic agent selected from the group consisting of precipitated silica, fumed silica, an organoclay, a metal soap, and a metal soap complex.

19. The formulation of claim 10 further comprising at least one additive selected from the group consisting of an organomolybdenum complex, an organomolybdenum thiocarbamate, and an organothiocarbamate.

20. A method of making an MR fluid comprising:

blending a carrier fluid including a polyalphaolefin and a plasticizer,

adding a fluorocarbon grease having an NLGI grade of between about 1 and 3, and

dispersing magnetizable particles in the carrier fluid.

21. The method of claim 20 wherein blending the carrier fluid comprises blending about 50-90% by volume polyalphaolefin with about 10-50% by volume plasticizer.

22. The method of claim 20 wherein the thixotropic agent is added in an amount of about 20 to 40% by weight of the carrier fluid.

23. The method of claim 20 further comprising adding an overbased sulfonate additive.