Ferrofluid composition and process
First Claim
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1. An improved ferrofluid composition comprising:
- a plurality of magnetic particles;
a silane-based surface modifier adsorbed on said plurality of magnetic particles as a surfactant-accepting layer, said surface modifier having a small enough molecular weight sufficient to be a nondispersant and having little or no individuality compared to the individuality of a surfactant;
at least one surfactant coating over said silane-based surface modifier in the outer layers of said plurality of magnetic particles; and
a carrier liquid.
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Abstract
The invention relates to a composition and process for producing a chemically stable magnetic fluid comprising a plurality of magnetic particles covered first with a small molecular weight surface modifier, which is a nondispersant and acts as a surfactant-accepting layer, and then with at least one surfactant. The surface modifier/surfactant coated magnetic particles are then suspended in a silicone oil-based, hydrocarbon oil-based or an ester oil-based carrier liquid.
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Citations
44 Claims
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1. An improved ferrofluid composition comprising:
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a plurality of magnetic particles;
a silane-based surface modifier adsorbed on said plurality of magnetic particles as a surfactant-accepting layer, said surface modifier having a small enough molecular weight sufficient to be a nondispersant and having little or no individuality compared to the individuality of a surfactant;
at least one surfactant coating over said silane-based surface modifier in the outer layers of said plurality of magnetic particles; and
a carrier liquid. - View Dependent Claims (2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 19, 20, 21)
wherein R1 denotes one to three similar functional groups where each group is an alkyl radical having one to eight carbon atoms, R2 denotes a hydrolyzable radical of one to three atoms, and n is 1, 2 or 3. -
6. The composition of claim 5 wherein said hydrolyzable radical is chosen from the group consisting of alkoxides of one to three carbon atoms.
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7. The composition of claim 5 wherein said hydrolyzable radical is chloride.
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8. The composition of claim 1 wherein said silane-based surface modifier is selected from the group consisting of isobutyltrimethoxysilane, isobutyltriethoxysilane, dimethyidimethoxysilane, dimethydiethoxysilane, trimethylmethoxysilane, n-propyltrimethoxysilane, n-butyltrimethoxysilane, and isobutyltrichlorosilane.
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9. The composition of claim 1 wherein said surfactant is chosen from the class of surfactants consisting of cationic surfactants, anionic surfactants and nonionic surfactants and has a molecular weight of at least 150.
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10. The composition of claim 1 wherein said carrier fluid is an organic molecule compatible with at least one surfactant.
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11. The composition of claim 10 wherein said carrier fluid is one of a silicone-based carrier fluid, a hydrocarbon-based carrier fluid and an ester-based carrier fluid.
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12. The composition of claim 1 wherein said carrier fluid is a silicone oil-based carrier fluid, a hydrocarbon oil-based carrier fluid or an ester oil-based carrier fluid.
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13. The composition of claim 1 wherein said silane-based surface modifier is an alkyl alkoxy silane surface modifier or an alkyl chloro silane surface modifier.
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14. The composition of claim 1 further comprising an antioxidant in said improved ferrofluid composition.
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19. The composition of claim 1 wherein said silane-based surface modifier is represented by the formula
wherein R1 denotes one to three similar functional groups where each group is an alkyl radical having one to eight carbon atoms, R2 denotes a hydrolyzable radical of one to three atoms, and n is 1, 2 or 3. -
20. The magnetic fluid of claim 19 wherein said hydrolyzable radical is chosen from the group consiting of alkoxides of one to three carbon atoms.
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21. The magnetic fluid of claim 19 wherein said hydrolyzable radical is chloride.
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15. A magnetic fluid obtained by the process comprising:
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adsorbing a silane-based surface modifier onto a plurality of magnetic particles as a surfactant-accepting layer, said surface modifier having a sufficiently small molecular weight to be a nondispersant and having little or no individuality compared to the individuality of a surfactant;
coating at least one surfactant over said silane-based surface modifier in the outer layers of said plurality of magnetic particles; and
suspending said plurality of magnetic particles into a carrier liquid. - View Dependent Claims (16, 17, 18, 22, 23, 24, 25, 26, 27, 37, 38, 39, 40, 41, 42, 43)
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28. A method of making an improved ferrofluid composition, said method comprising:
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obtaining a plurality of magnetic particles suspended in a first solvent;
adsorbing a small molecular weight silane-based surface modifier on said plurality of magnetic particles, said surface modifier having a small enough molecular weight sufficient to be a nondispersant and having little or no individuality compared to the individuality of a surfactant;
coating said plurality of said surface-modifier adsorbed particles with at least one surfactant; and
suspending said plurality of coated magnetic particles in an oil-based carrier liquid. - View Dependent Claims (29, 30, 31, 32, 33, 34, 35, 36, 44)
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Specification