Low-temperature-resistant perfluoropolyether-based magnetic liquid and preparation method thereof

Abstract

The invention discloses a low-temperature-resistant perfluoropolyether-based magnetic liquid and a preparation method thereof. The perfluoropolyether-based magnetic liquid comprises boron nitride coated magnetic nanoparticles, a surface modifier and a base carrier liquid, wherein the base carrier liquid is a mixture of long-chain perfluoropolyether and a short-chain perfluorinated compound. The perfluoropolyether-based magnetic liquid with relatively high stability and relatively good low-temperature resistance is obtained by optimizing the formula of the base carrier liquid, and the perfluoropolyether-based magnetic liquid can stably work under a low-temperature working condition.

Description

Technical Field

[0001] The present invention belongs to the technical field of magnetic liquid preparation, and in particular, the present invention relates to a low-temperature resistant perfluoropolyether-based magnetic liquid and a preparation method thereof. Background Art

[0002] Magnetic liquid is a functional magnetic material formed by uniformly and stably dispersing magnetic nanoparticles coated with surfactants in a base carrier liquid. It has both the fluidity of liquid and the magnetic properties of solid. Due to its excellent magnetic response performance and fluidity, it is widely used in mechanical sealing, vibration reduction and drag reduction, biomedicine, surface lubrication and other fields. The existing magnetic liquid preparation technology usually includes the following steps: surface modification of magnetic particles, dispersion of particles in the base carrier liquid and optimization of the final liquid performance. Among them, the selection of the base carrier liquid plays a decisive role in the performance of the magnetic liquid. In traditional technology, a single solvent such as kerosene and engine oil is often used as the base carrier liquid, and the magnetic particles are coated with surfactants to achieve stable dispersion of the particles. At present, the magnetic liquid prepared by traditional methods has reached mature application. However, with the development of science and technology, the disadvantages of magnetic liquids prepared by traditional methods are also becoming increasingly apparent. For example, magnetic liquids are not stable enough, are not acid-resistant, are not radiation-resistant, and are easily ineffective at high and low temperatures. The application field is limited and cannot meet the needs of some complex industrial environments.

[0003] Perfluoropolyether and its derivatives are selected as the base liquid and surfactant of magnetic liquid due to their low temperature resistance, low saturated vapor pressure, non-flammability, chemical inertness, heat resistance, and chemical stability, and have extremely high application value. However, due to their hydrophobicity and oleophobicity, the surface-modified magnetic particles are easy to agglomerate, which makes the magnetic liquid less stable and less resistant to low temperatures.

[0004] In view of this, the present invention is proposed. Summary of the invention

[0005] The present invention aims to solve one of the technical problems in the related art at least to a certain extent. To this end, the present invention provides a low-temperature resistant perfluoropolyether-based magnetic liquid and a preparation method thereof.

[0006] In one aspect, an embodiment of the present invention provides a perfluoropolyether-based magnetic liquid, comprising boron nitride-coated magnetic nanoparticles, a surface modifier, and a base carrier liquid; wherein the base carrier liquid is a mixture of long-chain perfluoropolyether and short-chain perfluoro compound.

[0007] In some embodiments, the mass ratio of the long-chain perfluoropolyether to the short-chain perfluoro compound is (60% to 90%): (10% to 40%);

[0008] Optionally, the short-chain perfluoro compound includes at least one of perfluoroalkyl ether, perfluoroalkane, perfluoroester and perfluoroalkylamine.

[0009] In some embodiments, the molecular weight of the long-chain perfluoropolyether is >1000;

[0010] And / or, the molecular weight of the short-chain perfluorinated compound is ≤1000.

[0011] In some embodiments, the magnetic nanoparticles include Fe3O4, γ-Fe2O3, ferrite magnetic particles MFe2O4 or M 1-X Zn X At least one of Fe2O4; wherein M is selected from at least one of Mn, Co, Ni, Cu, Cd, Pb, Sn, Ca, Sr, Ba or Mg.

[0012] In some embodiments, the molecular weight of the surfactant is 1000 to 4000;

[0013] Optionally, the surfactant includes at least one of perfluoropolyether carboxylic acid, perfluoropolyether carboxylic acid ammonium salt, perfluoropolyether amide, and perfluoropolyether halide.

[0014] Another aspect of the present invention is to provide a method for preparing the above-mentioned perfluoropolyether-based magnetic liquid, comprising the following steps:

[0015] S1, preparation of magnetic nanoparticles by coprecipitation method;

[0016] S2, adding the magnetic nanoparticles and boron nitride into a polar solvent, stirring and mixing, to obtain a boron nitride@magnetic nanoparticle composite;

[0017] S3, dispersing the boron nitride@magnetic nanoparticle complex into a surfactant solution for modification reaction, and then subjecting the solution to magnetic separation, washing, and drying to obtain a modified boron nitride@magnetic nanoparticle complex;

[0018] S4, adding the modified boron nitride@magnetic nanoparticles composite into a base carrier liquid, and mixing by ball milling to obtain the perfluoropolyether-based magnetic liquid.

[0019] In some embodiments, in step S1, the reaction temperature of the coprecipitation method is 25-100° C., the reaction time is 1-60 min, and the stirring speed is 200-500 r / min.

[0020] In some embodiments, in step S2, the molar ratio of the magnetic nanoparticles to the boron nitride is (1-5):1, and the particle size of the boron nitride is 20-50 nm;

[0021] And / or, the polar solvent includes at least one of N-methylpyrrolidone, ethanol, and acetone;

[0022] And / or, the stirring and mixing time is 0.5 to 3 hours.

[0023] In some embodiments, in step S3, the molar ratio of the boron nitride@magnetic nanoparticle composite to the surfactant in the surfactant solution is 1:(0.1-1.0);

[0024] And / or, the reaction temperature of the modification reaction is 20-100° C., the stirring speed is 200-400 r / min, and the reaction time is 1-60 min.

[0025] In some embodiments, in step S4, the ball milling mixing time is 1 to 8 hours.

[0026] The advantages and beneficial effects of the embodiments of the present invention are as follows:

[0027] (1) The perfluoropolyether-based magnetic liquid prepared in the embodiment of the present invention not only has the advantages of conventional perfluoropolyether such as low temperature resistance, low saturated vapor pressure, non-flammability, chemical inertness, heat resistance, and chemical stability ignition point, but also has uniform particle distribution, no agglomeration, no sedimentation, and unchanged fluidity, while some conventional magnetic liquids have already frozen or cannot maintain fluidity due to excessive viscosity and lose their application value.

[0028] (2) The embodiments of the present invention can provide more adsorption sites for surfactants by activating and modifying the surface of magnetic nanoparticles, thereby making the magnetic nanoparticles and surfactants have stronger interactions. At the same time, it also has the characteristics of breaking the regularity between molecules and having a smaller specific surface area, which can inhibit the crystallization of the base carrier liquid and reduce the agglomeration of magnetic nanoparticles. The obtained magnetic liquid can work stably at low temperatures.

[0029] (3) In the embodiment of the present invention, a long-chain perfluoropolyether and a short-chain perfluoro compound are compounded as the base carrier liquid, wherein the long-chain perfluoropolyether has strong stability and is not easy to volatilize; the short-chain perfluoro compound has low intermolecular force, and the molecules are less likely to aggregate and form a crystal structure at low temperatures, and have a low freezing point. In this way, the base carrier liquid can be ensured to be stable and resistant to low temperatures. DETAILED DESCRIPTION

[0030] Embodiments of the present invention are described in detail below. The embodiments are exemplary and intended to be used to explain the present invention, but should not be construed as limiting the present invention.

[0031] Where values ​​are described herein as a range, it should be understood that such disclosure includes disclosure of all possible sub-ranges within that range, as well as specific values ​​falling within that range, regardless of whether a specific value or a specific sub-range is explicitly stated.

[0032] Herein, the words "comprises" and "includes" and variations thereof mean that other elements or integers which are permitted but not specifically described may be included.

[0033] In this article, the term "and / or" is merely a term used to describe the association relationship of associated objects, indicating that three relationships may exist. For example, A and / or B may represent three situations: A exists alone, A and B exist at the same time, and B exists alone.

[0034] In one aspect, an embodiment of the present invention provides a perfluoropolyether-based magnetic liquid, comprising boron nitride-coated magnetic nanoparticles, a surface modifier, and a base carrier liquid; wherein the base carrier liquid is a mixture of long-chain perfluoropolyether and short-chain perfluoro compound.

[0035] In some embodiments, the mass ratio of the long-chain perfluoropolyether to the short-chain perfluoro compound is (60% to 90%): (10% to 40%), non-limiting examples are: 60%: 40%, 70%: 30%, 75%: 25%, 80%: 20%, 90%: 10%, etc.;

[0036] Optionally, the short-chain perfluoro compound includes at least one of perfluoroalkyl ether, perfluoroalkane, perfluoroester and perfluoroalkylamine.

[0037] In some embodiments, the molecular weight of the long-chain perfluoropolyether is >1000, non-limiting examples include: 1500, 2000, 4000, 5000, etc.;

[0038] And / or, the molecular weight of the short-chain perfluorinated compound is ≤1000, non-limiting examples include 200, 500, 800, 1000, etc.

[0039] In some embodiments, the magnetic nanoparticles include Fe3O4, γ-Fe2O3, ferrite magnetic particles MFe2O4 or M 1-X Zn X At least one of Fe2O4; wherein M is selected from at least one of Mn, Co, Ni, Cu, Cd, Pb, Sn, Ca, Sr, Ba or Mg.

[0040] In some embodiments, the molecular weight of the surfactant is 1000-4000, non-limiting examples include: 1000, 2500, 3000, 4000, etc.;

[0041] Optionally, the surfactant includes at least one of perfluoropolyether carboxylic acid, perfluoropolyether carboxylic acid ammonium salt, perfluoropolyether amide, and perfluoropolyether halide.

[0042] Another aspect of the present invention is to provide a method for preparing the above-mentioned perfluoropolyether-based magnetic liquid, comprising the following steps:

[0043] S1, preparation of magnetic nanoparticles by coprecipitation method;

[0044] S2, adding the magnetic nanoparticles and boron nitride into a polar solvent, stirring and mixing, to obtain a boron nitride@magnetic nanoparticle composite;

[0045] S3, dispersing the boron nitride@magnetic nanoparticle complex into a surfactant solution for modification reaction, and then subjecting the solution to magnetic separation, washing, and drying to obtain a modified boron nitride@magnetic nanoparticle complex;

[0046] S4, adding the modified boron nitride@magnetic nanoparticles composite into a base carrier liquid, and mixing by ball milling to obtain the perfluoropolyether-based magnetic liquid.

[0047] In some embodiments, in step S1, the reaction temperature of the co-precipitation method is 25-100°C (non-limiting examples include 25°C, 50°C, 60°C, 75°C, 80°C, 100°C, etc.), the reaction time is 1-60min (non-limiting examples include 1min, 10min, 20min, 45min, 60min, etc.), and the stirring speed is 200-500r / min (non-limiting examples include 200r / min, 400r / min, 500r / min, etc.).

[0048] In some embodiments, in step S2, the molar ratio of the magnetic nanoparticles to the boron nitride is (1-5):1 (non-limiting examples include 1:1, 2:1, 3:1, 4:1, 5:1, etc.), and the particle size of the boron nitride is 20-50 nm (non-limiting examples include 20 nm, 30 nm, 45 nm, 50 nm, etc.);

[0049] And / or, the polar solvent includes at least one of N-methylpyrrolidone, ethanol, and acetone;

[0050] And / or, the stirring and mixing time is 0.5 to 3 hours, non-limiting examples include: 0.5 hours, 1 hour, 2 hours, 2.5 hours, 3 hours, etc.

[0051] In some embodiments, in step S3, the molar ratio of the boron nitride@magnetic nanoparticle composite to the surfactant in the surfactant solution is 1:(0.1-1.0), non-limiting examples include: 1:0.1, 1:0.2, 1:0.5, 1:0.8, 1:1.0, etc.;

[0052] And / or, the reaction temperature of the modification reaction is 20-100°C (non-limiting examples: 20°C, 50°C, 60°C, 75°C, 80°C, 100°C, etc.), the stirring speed is 200-400r / min (non-limiting examples: 200r / min, 350r / min, 400r / min, etc.), and the reaction time is 1-60min (non-limiting examples: 1min, 10min, 20min, 45min, 60min, etc.).

[0053] In some embodiments, in step S4, the ball milling mixing time is 1 to 8 hours, non-limiting examples include: 1 hour, 2 hours, 4 hours, 5 hours, 8 hours, etc.

[0054] The following are non-limiting examples and comparative examples of the present invention. It should be noted that the schemes of the comparative examples are not prior art and are only provided for comparison with the schemes of the embodiments and are not intended to limit the present invention. Unless otherwise specified, the various raw materials used in the embodiments and comparative examples are conventional commercial products or can be prepared by known methods.

[0055] Example 1

[0056] This embodiment provides a method for preparing a perfluoropolyether-based magnetic liquid, comprising the following steps:

[0057] S1, weigh 11g of FeCl3·6H2O and 9.7g of FeCl2·4H2O and dissolve them in 400mL of deionized water, control the stirring speed to 400r / min in a 45℃ water bath, stir for 10min to make it uniform; then add 50g of concentrated ammonia water dropwise to the mixed salt solution, continue heating and stirring for 40min, it can be observed that the mixed solution quickly changes from yellow to black, after the reaction is completed, separate the magnetic particles by magnetic separation, and repeatedly wash with deionized water until the pH of the washing solution is 7, to obtain Fe3O4 magnetic nanoparticles;

[0058] S2, dissolving 12 g of Fe3O4 magnetic nanoparticles prepared in step S1 and 1 g of BN nanopowder (lamellar structure, particle size of 20 nm) in 50 mL of ethanol, stirring and mixing at room temperature for 1 h to obtain a BN@Fe3O4 composite;

[0059] S3, dispersing the above BN@Fe3O4 complex into a perfluoropolyether carboxylic acid ammonium salt solution (prepared by compounding 2.5mL perfluoropolyether carboxylic acid, 1mL n-butylamine, and 20g concentrated ammonia water), controlling the molar ratio of BN@Fe3O4 complex to perfluoropolyether carboxylic acid ammonium salt to be 1:0.2, then heating the water bath to 80°C, controlling the stirring speed to 400r / min, and performing a modification reaction. After reacting for 60min, the reaction product was cooled to room temperature, the black solid was separated by magnetic separation, and washed with water to pH=7, and then vacuum dried at 60°C for 12h to obtain a modified BN@Fe3O4 complex;

[0060] S4, the modified BN@Fe3O4 composite is ground in a mortar and added to a mixture of perfluoropolyether and perfluorohexane (wherein the mass ratio of perfluoropolyether to perfluorohexane is 70%:30%, and the molecular weight of perfluoropolyether is 2000), and then loaded into a ball mill, vacuum ball milled and mixed for 6 hours to obtain a perfluoropolyether-based magnetic liquid.

[0061] The saturation magnetization intensity of the perfluoropolyether-based magnetic liquid prepared in this embodiment is 130Gs. It can work stably for a long time at a temperature of -70°C and is still in a stable state after standing for 1 hour. Its particles are evenly distributed without agglomeration or sedimentation, and can be used in some special working environments.

[0062] Example 2

[0063] This embodiment provides a method for preparing a perfluoropolyether-based magnetic liquid, comprising the following steps:

[0064] S1, weighing 11g of FeCl3·6H2O and dissolving it in 400mL of deionized water, stirring at 400r / min in a water bath at 45°C, stirring for 10min, then dropwise adding 50g of concentrated ammonia water, continuing heating and stirring for 40min, then magnetically separating the magnetic particles, and repeatedly washing with deionized water until the pH of the washing solution is 7, to obtain γ-Fe2O3 magnetic nanoparticles;

[0065] S2, dissolving 8 g of γ-Fe2O3 magnetic nanoparticles prepared in step S1 and 1 g of BN nanopowder (lamellar structure, particle size of 20 nm) in 50 mL of ethanol, stirring and mixing at room temperature for 1 h to obtain a BN@γ-Fe2O3 composite;

[0066] S3, dispersing the above BN@γ-Fe2O3 complex into a perfluoropolyether carboxylic acid ammonium salt solution (prepared by compounding 2.5mL perfluoropolyether carboxylic acid, 1mL n-butylamine, and 20g concentrated ammonia water), controlling the molar ratio of the BN@γ-Fe2O3 complex to the perfluoropolyether carboxylic acid ammonium salt to be 1:0.2, then heating the water bath to 80°C, controlling the stirring speed to 400r / min, and performing a modification reaction. After reacting for 60min, the reaction product was cooled to room temperature, magnetically separated to obtain a black solid, washed with water to pH=7, and then vacuum dried at 60°C for 12h to obtain a modified BN@γ-Fe2O3 complex;

[0067] S4, the modified BN@γ-Fe2O3 composite is ground in a mortar and added to a mixture of perfluoropolyether and perfluorohexane (wherein the mass ratio of perfluoropolyether to perfluorohexane is 70%:30%, and the molecular weight of perfluoropolyether is 2000), and then loaded into a ball mill, and vacuum ball milled for 6 hours to obtain a perfluoropolyether-based magnetic liquid.

[0068] The saturation magnetization intensity of the perfluoropolyether-based magnetic liquid prepared in this embodiment is 114Gs. It can work stably for a long time at a temperature of -70°C and is still in a stable state after standing for 1 hour. Its particles are evenly distributed without agglomeration or sedimentation, and can be used in some special working environments.

[0069] Example 3

[0070] This embodiment provides a method for preparing a perfluoropolyether-based magnetic liquid, comprising the following steps:

[0071] S1, weigh 11g of CoCl3·6H2O and 9.7g of FeCl2·4H2O and dissolve them in 400mL of deionized water, control the stirring speed to 400r / min in a 45℃ water bath, stir for 10min to make it uniform; then add 50g of concentrated ammonia water dropwise to the mixed salt solution, continue heating and stirring for 40min, it can be observed that the mixed solution quickly changes from yellow to black, after the reaction is completed, separate the magnetic particles by magnetic separation, and repeatedly wash with deionized water until the pH of the washing liquid is 7, to obtain CoFe2O4 magnetic nanoparticles;

[0072] S2, dissolving 12 g of CoFe2O4 magnetic nanoparticles prepared in step S1 and 1 g of BN nanopowder (lamellar structure, particle size of 20 nm) in 50 mL of ethanol, stirring and mixing at room temperature for 1 h to obtain a BN@CoFe2O4 composite;

[0073] S3, dispersing the above BN@CoFe2O4 complex into a perfluoropolyether carboxylic acid ammonium salt solution (prepared by compounding 2.5mL perfluoropolyether carboxylic acid, 1mL n-butylamine, and 20g concentrated ammonia water), controlling the molar ratio of the BN@CoFe2O4 complex to the perfluoropolyether carboxylic acid ammonium salt to be 1:0.2, then heating the water bath to 80°C, controlling the stirring speed to 400r / min, and performing a modification reaction. After reacting for 60min, the reaction product was cooled to room temperature, magnetically separated to obtain a black solid, washed with water to pH=7, and then vacuum dried at 60°C for 12h to obtain a modified BN@CoFe2O4 complex;

[0074] S4, the modified BN@CoFe2O4 composite is ground in a mortar and added to a mixture of perfluoropolyether and perfluorohexane (wherein the mass ratio of perfluoropolyether to perfluorohexane is 70%:30%, and the molecular weight of perfluoropolyether is 2000), and then loaded into a ball mill, and vacuum ball milled for 6 hours to obtain a perfluoropolyether-based magnetic liquid.

[0075] The saturation magnetization intensity of the perfluoropolyether-based magnetic liquid prepared in this embodiment is 123Gs. It can work stably for a long time at a temperature of -70°C and is still in a stable state after standing for 1 hour. Its particles are evenly distributed without agglomeration or sedimentation, and can be used in some special working environments.

[0076] Example 4

[0077] This embodiment provides a method for preparing a perfluoropolyether-based magnetic liquid, comprising the following steps:

[0078] S1, weigh 11g of FeCl3·6H2O and 9.7g of FeCl2·4H2O and dissolve them in 400mL of deionized water, control the stirring speed to 400r / min in a 45℃ water bath, stir for 10min to make it uniform; then add 50g of concentrated ammonia water dropwise to the mixed salt solution, continue heating and stirring for 40min, it can be observed that the mixed solution quickly changes from yellow to black, after the reaction is completed, separate the magnetic particles by magnetic separation, and repeatedly wash with deionized water until the pH of the washing solution is 7, to obtain Fe3O4 magnetic nanoparticles;

[0079] S2, dissolving 12 g of Fe3O4 magnetic nanoparticles prepared in step S1 and 1 g of BN nanopowder (lamellar structure, particle size of 20 nm) in 50 mL of ethanol, stirring and mixing at room temperature for 1 h to obtain a BN@Fe3O4 composite;

[0080] S3, dispersing the above BN@Fe3O4 complex into a perfluoropolyether carboxylic acid ammonium salt solution (prepared by compounding 2.5mL perfluoropolyether carboxylic acid, 1mL n-butylamine, and 20g concentrated ammonia water), controlling the molar ratio of BN@Fe3O4 complex to perfluoropolyether carboxylic acid ammonium salt to be 1:0.2, then heating the water bath to 80°C, controlling the stirring speed to 400r / min, and performing a modification reaction. After reacting for 60min, the reaction product was cooled to room temperature, the black solid was separated by magnetic separation, and washed with water to pH=7, and then vacuum dried at 60°C for 12h to obtain a modified BN@Fe3O4 complex;

[0081] S4, grinding the modified BN@Fe3O4 composite in a mortar and adding it to a mixture of perfluoropolyether and perfluorohexane (wherein the mass ratio of perfluoropolyether to perfluorohexane is 80%:20%, and the molecular weight of perfluoropolyether is 2000), and then loading it into a ball mill, vacuum ball milling and mixing for 6 hours to obtain a perfluoropolyether-based magnetic liquid.

[0082] The saturation magnetization intensity of the perfluoropolyether-based magnetic liquid prepared in this embodiment is 132Gs. It can work stably for a long time at a temperature of -50°C and is still in a stable state after standing for 1 hour. Its particles are evenly distributed without agglomeration or sedimentation, and can be used in some special working environments.

[0083] Example 5

[0084] This embodiment provides a method for preparing a perfluoropolyether-based magnetic liquid, comprising the following steps:

[0085] S1, weigh 11g of FeCl3·6H2O and 9.7g of FeCl2·4H2O and dissolve them in 400mL of deionized water, control the stirring speed to 400r / min in a 45℃ water bath, stir for 10min to make it uniform; then add 50g of concentrated ammonia water dropwise to the mixed salt solution, continue heating and stirring for 40min, it can be observed that the mixed solution quickly changes from yellow to black, after the reaction is completed, separate the magnetic particles by magnetic separation, and repeatedly wash with deionized water until the pH of the washing solution is 7, to obtain Fe3O4 magnetic nanoparticles;

[0086] S2, dissolving 12 g of Fe3O4 magnetic nanoparticles prepared in step S1 and 1 g of BN nanopowder (lamellar structure, particle size of 20 nm) in 50 mL of ethanol, stirring and mixing at room temperature for 1 h to obtain a BN@Fe3O4 composite;

[0087] S3, dispersing the above BN@Fe3O4 complex into a perfluoropolyether carboxylic acid ammonium salt solution (prepared by compounding 2.5mL perfluoropolyether carboxylic acid, 1mL n-butylamine, and 20g concentrated ammonia water), controlling the molar ratio of BN@Fe3O4 complex to perfluoropolyether carboxylic acid ammonium salt to be 1:0.2, then heating the water bath to 80°C, controlling the stirring speed to 400r / min, and performing a modification reaction. After reacting for 60min, the reaction product was cooled to room temperature, the black solid was separated by magnetic separation, and washed with water to pH=7, and then vacuum dried at 60°C for 12h to obtain a modified BN@Fe3O4 complex;

[0088] S4, grinding the modified BN@Fe3O4 composite in a mortar and adding it to a mixture of perfluoropolyether and perfluorohexane (wherein the mass ratio of perfluoropolyether to perfluorohexane is 90%:10%, and the molecular weight of perfluoropolyether is 2000), and then loading it into a ball mill, vacuum ball milling and mixing for 6 hours to obtain a perfluoropolyether-based magnetic liquid.

[0089] The saturation magnetization intensity of the perfluoropolyether-based magnetic liquid prepared in this embodiment is 133. It can work stably for a long time at a temperature of -30°C and is still in a stable state after standing for 1 hour. Its particles are evenly distributed without agglomeration or sedimentation, and can be used in some special working environments.

[0090] Comparative Example 1

[0091] This comparative example provides a method for preparing a perfluoropolyether-based magnetic liquid, comprising the following steps:

[0092] S1, weigh 11g of FeCl3·6H2O and 9.7g of FeCl2·4H2O and dissolve them in 400mL of deionized water, control the stirring speed to 400r / min in a 45℃ water bath, stir for 10min to make it uniform; then add 50g of concentrated ammonia water dropwise to the mixed salt solution, continue heating and stirring for 40min, it can be observed that the mixed solution quickly changes from yellow to black, after the reaction is completed, separate the magnetic particles by magnetic separation, and repeatedly wash with deionized water until the pH of the washing solution is 7, to obtain Fe3O4 magnetic nanoparticles;

[0093] S2, dissolving 12 g of Fe3O4 magnetic nanoparticles prepared in step S1 and 1 g of BN nanopowder (lamellar structure, particle size of 20 nm) in 50 mL of ethanol, stirring and mixing at room temperature for 1 h to obtain a BN@Fe3O4 composite;

[0094] S3, dispersing the above BN@Fe3O4 complex into a perfluoropolyether carboxylic acid ammonium salt solution (prepared by compounding 2.5mL perfluoropolyether carboxylic acid, 1mL n-butylamine, and 20g concentrated ammonia water), then heating the water bath to 80°C, controlling the stirring speed to 400r / min, and performing a modification reaction. After reacting for 60min, the reaction product was cooled to room temperature, and the black solid was separated by magnetic separation, washed with water to pH=7, and then vacuum dried at 60°C for 12h to obtain a modified BN@Fe3O4 complex;

[0095] S4, the modified BN@Fe3O4 composite was ground in a mortar and added to the perfluoropolyether, and then placed in a ball mill, and the mixture was mixed by vacuum ball milling for 6 hours to obtain a perfluoropolyether-based magnetic liquid.

[0096] The saturation magnetization intensity of the perfluoropolyether-based magnetic liquid prepared in this comparative example is 130 Gs, but it almost loses fluidity at -20°C and cannot meet the requirements of magnetic liquid sealing under low temperature conditions.

[0097] Comparative Example 2

[0098] This comparative example provides a method for preparing a magnetic liquid, comprising the following steps:

[0099] S1, weigh 11g of FeCl3·6H2O and 9.7g of FeCl2·4H2O and dissolve them in 400mL of deionized water, control the stirring speed to 400r / min in a 45℃ water bath, stir for 10min to make it uniform; then add 50g of concentrated ammonia water dropwise to the mixed salt solution, continue heating and stirring for 40min, it can be observed that the mixed solution quickly changes from yellow to black, after the reaction is completed, separate the magnetic particles by magnetic separation, and repeatedly wash with deionized water until the pH of the washing solution is 7, to obtain Fe3O4 magnetic nanoparticles;

[0100] S2, dissolving 12 g of Fe3O4 magnetic nanoparticles prepared in step S1 and 1 g of BN nanopowder (lamellar structure, particle size of 20-50 nm) in 50 mL of ethanol, stirring and mixing at room temperature for 1 h to obtain a BN@Fe3O4 composite;

[0101] S3, dispersing the above BN@Fe3O4 complex into a perfluoropolyether carboxylic acid ammonium salt solution (prepared by compounding 2.5mL perfluoropolyether carboxylic acid, 1mL n-butylamine, and 20g concentrated ammonia water), then heating the water bath to 80°C, controlling the stirring speed to 400r / min, and performing a modification reaction. After reacting for 60min, the reaction product was cooled to room temperature, and the black solid was separated by magnetic separation, washed with water to pH=7, and then vacuum dried at 60°C for 12h to obtain a modified BN@Fe3O4 complex;

[0102] S4, the modified BN@Fe3O4 composite was ground in a mortar and added to perfluorohexane, and then placed in a ball mill, and the mixture was mixed by vacuum ball milling for 6 hours to obtain a magnetic liquid.

[0103] The magnetic liquid prepared in this comparative example has poor stability and is very likely to fail in low-temperature conditions, and cannot meet the use requirements of magnetic liquid sealing under low-temperature conditions.

[0104] In the present invention, the terms "one embodiment", "some embodiments", "examples", "specific examples", or "some examples" etc. mean that the specific features, structures, materials or characteristics described in conjunction with the embodiment or example are included in at least one embodiment or example of the present invention. In this specification, the schematic representations of the above terms do not necessarily refer to the same embodiment or example. Moreover, the described specific features, structures, materials or characteristics may be combined in any one or more embodiments or examples in a suitable manner. In addition, those skilled in the art may combine and combine the different embodiments or examples described in this specification and the features of the different embodiments or examples, without contradiction.

[0105] Although the embodiments of the present invention have been shown and described above, it is to be understood that the above embodiments are exemplary and are not to be construed as limitations of the present invention. A person skilled in the art may change, modify, replace and vary the above embodiments within the scope of the present invention.

Claims

1. A perfluoropolyether-based magnetic liquid, characterized in that: The invention comprises magnetic nanoparticles coated with boron nitride, a surface modifier and a base carrier liquid; wherein the base carrier liquid is a mixture of long-chain perfluoropolyether and short-chain perfluoro compound.

2. The perfluoropolyether-based magnetic liquid according to claim 1, characterized in that: The mass ratio of the long-chain perfluoropolyether to the short-chain perfluoro compound is (60% to 90%): (10% to 40%); Optionally, the short-chain perfluoro compound includes at least one of perfluoroalkyl ether, perfluoroalkane, perfluoroester and perfluoroalkylamine.

3. The perfluoropolyether-based magnetic liquid according to claim 2, characterized in that: The molecular weight of the long-chain perfluoropolyether is >1000; And / or, the molecular weight of the short-chain perfluorinated compound is ≤1000.

4. The perfluoropolyether-based magnetic liquid according to claim 1, characterized in that: The magnetic nanoparticles include Fe3O4, γ-Fe2O3, ferrite magnetic particles MFe2O4 or M 1-X Zn X At least one of Fe2O4; wherein M is selected from at least one of Mn, Co, Ni, Cu, Cd, Pb, Sn, Ca, Sr, Ba or Mg.

5. The perfluoropolyether-based magnetic liquid according to claim 1, characterized in that: The molecular weight of the surfactant is 1000 to 4000; Optionally, the surfactant includes at least one of perfluoropolyether carboxylic acid, perfluoropolyether carboxylic acid ammonium salt, perfluoropolyether amide, and perfluoropolyether halide.

6. A method for preparing a perfluoropolyether-based magnetic liquid according to any one of claims 1 to 5, characterized in that: The steps include: S1, preparation of magnetic nanoparticles by coprecipitation method; S2, adding the magnetic nanoparticles and boron nitride into a polar solvent, stirring and mixing, to obtain a boron nitride@magnetic nanoparticle composite; S3, dispersing the boron nitride@magnetic nanoparticle complex into a surfactant solution for modification reaction, and then subjecting the solution to magnetic separation, washing, and drying to obtain a modified boron nitride@magnetic nanoparticle complex; S4, adding the modified boron nitride@magnetic nanoparticles composite into a base carrier liquid, and mixing by ball milling to obtain the perfluoropolyether-based magnetic liquid.

7. The method for preparing a perfluoropolyether-based magnetic liquid according to claim 6, characterized in that: In the step S1, the reaction temperature of the coprecipitation method is 25-100° C., the reaction time is 1-60 min, and the stirring speed is 200-500 r / min.

8. The method for preparing a perfluoropolyether-based magnetic liquid according to claim 6, characterized in that: In the step S2, the molar ratio of the magnetic nanoparticles to the boron nitride is (1-5):1, and the particle size of the boron nitride is 20-50 nm; And / or, the polar solvent includes at least one of N-methylpyrrolidone, ethanol, and acetone; And / or, the stirring and mixing time is 0.5 to 3 hours.

9. The method for preparing a perfluoropolyether-based magnetic liquid according to claim 6, characterized in that: In the step S3, the molar ratio of the boron nitride@magnetic nanoparticle composite to the surfactant in the surfactant solution is 1:(0.1-1.0); And / or, the reaction temperature of the modification reaction is 20-100° C., the stirring speed is 200-400 r / min, and the reaction time is 1-60 min.

10. The method for preparing a perfluoropolyether-based magnetic liquid according to claim 6, characterized in that: In the step S4, the ball milling mixing time is 1 to 8 hours.