Composition and method of making a ferrofluid having an improved chemical stability
First Claim
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1. A magnetic fluid composition comprising:
- a carrier liquid; and
a plurality of magnetic particles coated with at least one surfactant and a fluorocarbon-silane surface modifier, said surface modifier being a nondispersant and improving the acid resistance of said magnetic fluid.
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Abstract
The invention relates to a composition and a process for producing a magnetic fluid comprising finely divided magnetic particles covered with at least one surfactant. A fluorocarbon-silane surface modifier is employed which is added to cover the free oxidizable exterior surface of the outer layer of the particles to increase the acid resistance of the colloid.
30 Citations
37 Claims
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1. A magnetic fluid composition comprising:
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a carrier liquid; and
a plurality of magnetic particles coated with at least one surfactant and a fluorocarbon-silane surface modifier, said surface modifier being a nondispersant and improving the acid resistance of said magnetic fluid. - View Dependent Claims (2, 3, 4, 5, 6, 7, 8, 9, 10, 11)
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6. The composition of claim 1 wherein said surface modifier is a fluorocarbon-silane surface modifier represented by the formula
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7. The composition of claim 1 wherein said surface modifier is a fluorocarbon-silane surface modifier represented by the formula
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8. The composition of claim 1 wherein said surface modifier is one of a fluoroalkyl alkoxy silane and a fluoroalkyl alkyl alkoxy silane.
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9. The composition of claim 1 wherein said surface modifier is selected from the group consisting of heptadecafluorodecyltrimethoxysilane, tridecafluorooctyltrimethoxysilane, heptadecafluorodecyltriethoxysilane, tridecafluorooctyltriethoxysilane, trifluoropropyltrimethoxysilane, and trifluoropropylmethyldimethoxysilane.
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10. The composition of claim 1 wherein said plurality of magnetic particles are ferrite which have a diameter size ranging from about thirty to about one hundred fifty angstroms.
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11. The composition of claim 1 wherein said at least one surfactant is selected from the class of surfactants consisting of cationic surfactants, anionic surfactants and nonionic surfactants.
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12. A magnetic fluid composition comprising:
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a carrier liquid;
a plurality of magnetic particles dispersed within said carrier liquid wherein said plurality of magnetic particles are coated with at least one surfactant; and
a fluorocarbon-silane surface modifier coated on said plurality of magnetic particles wherein said surface modifier is one of a fluoroalkyl alkoxy silane and a fluoroalkyl alkyl alkoxy silane, said surface modifier being a nondispersant and improving the acid resistance of said magnetic fluid. - View Dependent Claims (13, 14, 15)
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14. The composition of claim 12 wherein said surface modifier is a fluorocarbon-silane surface modifier represented by the formulae
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15. The composition of claim 12 wherein said surface modifier is selected from the group consisting of heptadecafluorodecyltrimethoxysilane, tridecafluorooctyltrimethoxysilane, heptadecafluorodecyltriethoxysilane, tridecafluorooctyltriethoxysilane, trifluoropropyltrimethoxysilane, and trifluoropropylmethyldimethoxysilane.
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16. A method of making a magnetic fluid composition, said method comprising the steps of:
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preparing a solvent-based magnetic fluid having a plurality of magnetic particles coated with at least one of a cationic, an anionic and a nonionic surfactant;
adding to said solvent-based magnetic fluid a low molecular weight fluorocarbon-silane surface modifier to improve the acid resistance of said composition wherein said surface modifier is represented by the formula - View Dependent Claims (17, 18, 19, 20, 21, 22)
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23. A method of making an improved magnetic fluid composition from a magnetic fluid comprising a low vapor-pressure carrier liquid containing a plurality of magnetic particles coated with at least one surfactant, said method comprising the steps of:
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flocking said magnetic fluid with a solvent compatible with said carrier liquid;
separating said solvent containing carrier liquid from said plurality of surfactant-coated magnetic particles;
re-suspending said plurality of surfactant-coated magnetic particles in a compatible solvent base forming a solvent base mixture;
adding a low molecular weight fluorocarbon-silane surface modifier to improve the acid resistance of said plurality of surfactant-coated magnetic particles wherein said surface modifier is represented by the formulae - View Dependent Claims (24, 25, 26, 27, 28, 29)
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30. A method of making an improved magnetic fluid composition from a magnetic fluid comprising a low molecular weight carrier liquid containing a plurality of magnetic particles coated with at least one surfactant, said method comprising:
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mixing an amount of an organic solvent with an amount of said magnetic fluid forming a fluid-solvent mix;
adding a low molecular weight fluorocarbon-silane surface modifier to said fluid-solvent mix forming a treated fluid mix to improve the acid resistance of said plurality of surfactant-coated magnetic particles wherein said surface modifier is represented by the formulae - View Dependent Claims (31, 32)
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33. A magnetic fluid obtained by the process comprising:
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obtaining a solvent-based magnetic fluid having a plurality of magnetic particles coated with at least one surfactant;
adding to said solvent-based magnetic fluid a fluorocarbon-silane surface modifier, said surface modifier being a nondispersant and improving the acid resistance of said magnetic fluid;
removing about half of the solvent from said solvent-based magnetic fluid; and
adding a compatible high molecular weight organic carrier liquid to said magnetic fluid. - View Dependent Claims (34, 35, 36, 37)
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35. The magnetic fluid of claim 33 wherein said surface modifier is one of a fluoroalkyl alkoxy silane and a fluoroalkyl alkyl alkoxy silane.
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36. The magnetic fluid of claim 34 wherein said R1 further comprises the formula R1aR1b wherein R1a denotes a fluoroalkyl radical having one to eight carbon atoms and R1b denotes an alkyl radical having one to two carbon atoms.
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37. The magnetic fluid of claim 33 wherein said surface modifier is selected from the group consisting of heptadecafluorodecyltrimethoxysilane, tridecafluorooctyltrimethoxysilane, heptadecafluorodecyltriethoxysilane, tridecafluorooctyltriethoxysilane, trifluoropropyltrimethoxysilane, and trifluoropropylmethyldimethoxysilane.
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Specification