Perfluoropolyether-based magnetic liquid and preparation method thereof

Abstract

The invention provides perfluoropolyether-based magnetic liquid and a preparation method thereof, and belongs to the technical field of magnetic liquid. The perfluoropolyether-based magnetic liquid comprises nano magnetic particles, a pretreated perfluoropolyether surfactant and a perfluoropolyether-based carrier liquid, wherein the pretreated perfluoropolyether surfactant is prepared by carrying out grafting reaction on the perfluoropolyether surfactant and acid anhydride. The perfluoropolyether-based magnetic liquid has relatively high colloidal stability and thermal stability, and can be applied to long-term stable work under a high-temperature working condition.

Description

Technical Field

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

[0002] Magnetic liquid is a new type of composite nanomaterial. It is formed by uniformly dispersing magnetic particles with nanometer diameter in a base carrier liquid after modification with a suitable surfactant to form a stable colloidal system. This material has both the fluidity and magnetism of liquid and can be used for lubrication, manufacturing magnetic liquid sealing devices, sensors and shock absorbers, etc. It is widely used in many high-tech fields such as aerospace, electronic technology, mechanical chemical industry, energy metallurgy, instrumentation, biomedicine, etc. Magnetic liquid relies on surfactants to achieve stable suspension of nanomagnetic particles in a liquid environment. The surfactant molecules need to provide sufficient repulsive force to prevent the nanomagnetic particles from agglomerating under the action of gravity, inter-particle magnetic force or van der Waals force.

[0003] In the existing magnetic liquid preparation technology, ester and diester oils, mineral oils and water are common magnetic liquid base carriers. However, these substances are limited by their own physical and chemical properties and will produce a large amount of volatility or thermal decomposition of molecules at high temperatures. The loss or denaturation of the base carrier will cause the magnetic liquid to stratify into solid particles and liquid, which will eventually make the magnetic liquid unusable. Perfluoropolyether is a special colorless, odorless, transparent liquid perfluoro compound with a structure similar to long-chain hydrocarbon polymers, but the H atoms in the molecular chain are replaced by F atoms. Due to the high strength and stability of the CF chemical bond, the strong electronegativity of the F atom also has a certain shielding effect on the internal long-chain structure. Perfluoropolyether has the advantages of high temperature resistance, low saturated vapor pressure, non-flammability, high thermal stability and stable chemical properties. When it is used as the base carrier of the magnetic liquid, it can effectively improve the performance of the magnetic liquid in a high temperature environment and has a strong application value. Perfluoropolyether is prepared by photo-oxidation catalytic polymerization or anionic polymerization of perfluoromonomers. The structure of the perfluoropolyether obtained by polymerization is different due to different monomers and different synthesis methods. According to the molecular structure of perfluoropolyether, it can be divided into K-type, Y-type, Z-type and D-type perfluoropolyether. The weight average molecular weight is generally around 1000-20000. The higher the molecular weight of perfluoropolyether, the lower its volatility and the enhanced thermal stability. In order for the magnetic fluid to work normally in a high temperature environment, it is necessary to use a high molecular weight perfluoropolyether-based carrier liquid and adapt the corresponding high molecular weight perfluoropolyether surfactant.

[0004] However, since the reaction and adsorption of perfluoropolyether surfactant molecules, such as perfluoropolyether carboxylic acid or perfluoropolyether amine, with nanomagnetic particles is achieved by relying on a single active group at the end, when the molecular weight is high, the flexibility of the polyether chain will cause the surfactant molecules to curl and agglomerate, reducing the probability of contact and collision between the end active groups and the surface of the nanomagnetic particles, and increasing the difficulty of the surfactant to perform surface modification reactions, it is difficult to obtain a long-term stable high-temperature resistant perfluoroether-based magnetic liquid. For example, patent application document CN201310692408.5 discloses a method for preparing a perfluoropolyether oil-based magnetic liquid, which is prepared from three parts: bare Fe3O4 magnetic nanoparticles, perfluoropolyether carboxylic acid surfactants, and perfluoropolyether oil-based carrier liquid. First, a chemical coprecipitation method is used to prepare bare Fe3O4 nanoparticles with an average particle size of 10nm; then a perfluoropolyether carboxylic acid surfactant is used to modify it; finally, the modified Fe3O4 magnetic nanoparticles are blended with a perfluoropolyether oil-based carrier liquid by high-energy ball milling or ultrasonic oscillation to form a perfluoropolyether oil-based magnetic liquid. Perfluoropolyether carboxylic acid is used as a surfactant. During the preparation process, the perfluoropolyether carboxylic acid surfactant is directly added to the aqueous solution to react with the magnetic nanoparticles. However, as the molecular weight increases, the dispersibility and reactivity of the perfluoropolyether carboxylic acid in the aqueous phase decrease, making it difficult to obtain a high-stability, high-temperature resistant perfluoropolyether magnetic liquid.

[0005] There are also some high-stability, high-temperature resistant perfluoropolyether-based magnetic liquids in the related art, but their magnetic properties are relatively low. For example, patent application document CN202210777827.8 discloses a low-temperature resistant perfluoropolyether-based magnetic liquid and a preparation method thereof. The perfluoropolyether-based magnetic liquid is prepared from magnetic nanoparticles coated with graphene oxide, a surfactant and a base carrier liquid; wherein the surfactant is a perfluoroalkylamine, a perfluoropolyether carboxylic acid or a mixture thereof; and the base carrier liquid is a perfluoropolyether oil. The preparation method of the above-mentioned perfluoropolyether-based magnetic liquid uses a surfactant to perform surface coating modification on the magnetic nanoparticles coated with graphene oxide to obtain modified magnetic nanoparticles coated with graphene oxide, and then disperses the modified magnetic nanoparticles coated with graphene oxide in a perfluoropolyether oil-based carrier liquid to prepare a perfluoropolyether-based magnetic liquid. Although this method uses graphene oxide to pre-modify magnetic nanoparticles, it provides more adsorption sites, thereby improving the reactivity of subsequent surfactants, and ultimately improving the stability of the perfluoropolyether-based magnetic liquid. However, this method will introduce non-magnetic solid matter, which will reduce the magnetic properties of the magnetic liquid and thus affect its performance. Summary of the invention

[0006] The present invention aims to solve at least one of the technical problems in the related art to a certain extent. To this end, an embodiment of the present invention provides a perfluoropolyether-based magnetic liquid and a preparation method thereof, wherein the perfluoropolyether-based magnetic liquid has high colloidal stability and thermal stability and can be applied to long-term stable operation under high temperature conditions.

[0007] The embodiment of the present invention provides a perfluoropolyether-based magnetic liquid, comprising nanomagnetic particles, a pretreated perfluoropolyether surfactant and a perfluoropolyether-based carrier liquid, wherein the pretreated perfluoropolyether surfactant is prepared by grafting a perfluoropolyether surfactant with an acid anhydride.

[0008] The advantages and technical effects brought by the perfluoropolyether-based magnetic liquid of the embodiment of the present invention are as follows:

[0009] The pretreated perfluoropolyether surfactant is obtained by introducing an active carbon chain into the end group of the perfluoropolyether surfactant. Compared with the perfluoropolyether surfactant, the pretreated perfluoropolyether surfactant has better dispersibility in an aqueous environment and better reaction activity with nanomagnetic particles, and can make the nanomagnetic particles more stably dispersed in a perfluoropolyether-based carrier liquid. Therefore, compared with the perfluoropolyether-based magnetic liquid in the related art, the perfluoropolyether-based magnetic liquid in the embodiment of the present invention has higher colloidal stability and thermal stability, so it can be applied to long-term stable operation under high temperature conditions.

[0010] In some embodiments, the perfluoropolyether surfactant is a perfluoropolyether alcohol and / or a perfluoropolyether amine.

[0011] In some embodiments, the weight average molecular weight of the perfluoropolyether surfactant is 5,000 to 20,000.

[0012] In some embodiments, the weight average molecular weight of the perfluoropolyether surfactant is 10,000 to 20,000.

[0013] In some embodiments, the weight average molecular weight of the perfluoropolyether-based carrier liquid is 5,000 to 20,000.

[0014] In some embodiments, the weight average molecular weight of the perfluoropolyether-based carrier liquid is 10,000 to 20,000.

[0015] In some embodiments, the nanomagnetic particles are at least one of Fe3O4, γ-Fe2O3 and CoFe2O4.

[0016] In some embodiments, the anhydride is at least one of succinic anhydride, glutaric anhydride, and adipic anhydride.

[0017] In some embodiments, the mass ratio of the pretreated perfluoropolyether surfactant to the nanomagnetic particles is 1:3 to 1:5.

[0018] In some embodiments, the mass ratio of the nanomagnetic particles to the perfluoropolyether-based carrier liquid is 1:2 to 1:10.

[0019] In addition, an embodiment of the present invention further provides a method for preparing a perfluoropolyether-based magnetic liquid, comprising the following steps:

[0020] S1. The perfluoropolyether surfactant is dissolved in a transition liquid, and then anhydride and a catalyst are added to the transition liquid, and the transition liquid is evaporated after the grafting reaction to obtain a pretreated perfluoropolyether surfactant;

[0021] S2. The nanomagnetic particles are dispersed in ultrapure water, and then the pretreated perfluoropolyether surfactant is added dropwise, and then the coated material is washed and dried to obtain coated nanomagnetic particles;

[0022] S3. Dispersing the coated nanomagnetic particles in a perfluoropolyether-based carrier liquid to obtain a perfluoropolyether-based magnetic liquid.

[0023] The advantages and technical effects brought by the preparation method of the embodiment of the present invention are:

[0024] The preparation method of the embodiment of the present invention introduces active carbon chains into the end groups of the perfluoropolyether surfactant by grafting reaction of the perfluoropolyether surfactant molecules using acid anhydride, thereby improving the dispersibility of the perfluoropolyether surfactant in an aqueous environment and the reaction activity with nanomagnetic particles, making the nanomagnetic particles more stably dispersed in the perfluoropolyether-based carrier liquid, thereby improving the colloidal stability and thermal stability of the magnetic liquid, and can be used for long-term stable operation under high temperature conditions.

[0025] In some embodiments, in step S1, the catalyst is 4-dimethylaminopyridine and / or triethylamine.

[0026] In some embodiments, in step S1, the temperature of the grafting reaction is 80-120° C., and the time of the grafting reaction is 6-12 hours.

[0027] In some embodiments, in step S1, a perfluoropolyether surfactant is dissolved in a transition liquid, and then an excess of anhydride and a catalyst are added to the transition liquid. After the grafting reaction, ultrapure water is used to dissolve and wash the residual anhydride and catalyst for 3 to 5 times, and then the transition liquid is evaporated to obtain a pretreated perfluoropolyether surfactant.

[0028] In some embodiments, in step S2, the nanomagnetic particles are dispersed in ultrapure water, the temperature in the water bath is adjusted to 70-100°C and stirred, then the pretreated perfluoropolyether surfactant is added dropwise, stirred at 300-1000 rpm for 15-30 min, the coated material is washed and dried to obtain the coated nanomagnetic particles. BRIEF DESCRIPTION OF THE DRAWINGS

[0029] Figure 1 is the structural formula of the pretreated perfluoropolyether surfactant in the perfluoropolyether-based magnetic liquid of the embodiment of the present invention.

[0030] Figure 2 This is the magnetization curve of the perfluoropolyether-based magnetic liquid of Example 1.

[0031] Figure 3 This is the magnetization curve of the perfluoropolyether-based magnetic liquid of Example 2.

[0032] Figure 4 This is a photograph of the perfluoropolyether-based magnetic liquid of Example 1 after 24 hours of stability testing.

[0033] Figure 5 This is a photograph of the perfluoropolyether-based magnetic liquid of Example 2 after 24 hours of stability testing.

[0034] Figure 6 This is a photograph of the perfluoropolyether-based magnetic liquid of Comparative Example 1 after 24 hours of stability testing.

[0035] Figure 7 This is a photograph of the perfluoropolyether-based magnetic liquid of Example 1 after 72 hours of stability testing.

[0036] Figure 8 This is a photograph of the perfluoropolyether-based magnetic liquid of Example 3 after 72 hours of stability testing.

[0037] Fig. 9 This is a photograph of the perfluoropolyether-based magnetic liquid of Example 4 after 72 hours of stability testing. DETAILED DESCRIPTION

[0038] Embodiments of the present invention are described in detail below, and examples of the embodiments are shown in the accompanying drawings. The embodiments described below with reference to the accompanying drawings are exemplary and intended to be used to explain the present invention, but should not be understood as limiting the present invention.

[0039] The embodiment of the present invention provides a perfluoropolyether-based magnetic liquid, comprising nanomagnetic particles, a pretreated perfluoropolyether surfactant and a perfluoropolyether-based carrier liquid, wherein the pretreated perfluoropolyether surfactant is prepared by grafting a perfluoropolyether surfactant with an acid anhydride.

[0040] The pretreated perfluoropolyether surfactant is obtained by introducing an active carbon chain into the end group of the perfluoropolyether surfactant. Compared with the perfluoropolyether surfactant, the pretreated perfluoropolyether surfactant has better dispersibility in an aqueous environment and better reaction activity with nanomagnetic particles, and can make the nanomagnetic particles more stably dispersed in a perfluoropolyether-based carrier liquid. Therefore, compared with the perfluoropolyether-based magnetic liquid in the related art, the perfluoropolyether-based magnetic liquid in the embodiment of the present invention has higher colloidal stability and thermal stability, so it can be applied to long-term stable operation under high temperature conditions.

[0041] In some embodiments, the magnetic liquid of the present invention does not include non-magnetic solid matter. Avoiding the addition of non-magnetic solid matter can enable the magnetic liquid to maintain a high magnetic performance.

[0042] In some embodiments, the perfluoropolyether surfactant is a perfluoropolyether alcohol and / or a perfluoropolyether amine.

[0043] The chemical structural formula of the perfluoropolyether alcohol is as follows:

[0044]

[0045] The chemical structural formula of the perfluoropolyetheramine is as follows:

[0046]

[0047] In some embodiments, the weight average molecular weight of the perfluoropolyether surfactant is 5000 to 20000, preferably 10000 to 20000. The higher the molecular weight of the perfluoropolyether surfactant, the lower its volatility and the enhanced thermal stability. Due to the presence of the pretreated perfluoropolyether surfactant, even if the high molecular weight perfluoropolyether surfactant is adapted, the high molecular weight perfluoropolyether surfactant can interact more strongly with the surface of the nanomagnetic particles, thereby improving the adsorption and coating effects of the surfactant without introducing non-magnetic substances to reduce the magnetic properties of the nanomagnetic particles.

[0048] In some embodiments, the weight average molecular weight of the perfluoropolyether-based carrier liquid is 5000 to 20000, preferably 10000 to 20000. High molecular weight perfluoropolyether surfactants and high molecular weight perfluoropolyether-based carrier liquids have the advantages of chemical inertness, oxidation resistance, low vapor pressure and ignition point of conventional perfluoropolyethers, and can also work normally in a higher temperature range, with high thermal stability, low volatility, uniform particle distribution, no agglomeration, and no sedimentation. The perfluoropolyether-based magnetic liquids in the related art are difficult to maintain good stability and magnetic properties while using high molecular weight raw materials, but the perfluoropolyether-based magnetic liquids of the embodiments of the present invention can achieve the above purposes.

[0049] In some embodiments, the nanomagnetic particles are at least one of Fe3O4, γ-Fe2O3 and CoFe2O4. The above nanomagnetic particles have good magnetic properties.

[0050] In some embodiments, the acid anhydride is at least one of succinic anhydride, glutaric anhydride and adipic anhydride. The above-mentioned types of acid anhydrides can introduce active carbon chains into the ends of perfluoropolyether surfactants. Preferably, the acid anhydride is glutaric anhydride and / or adipic anhydride. Figure 1 As shown, relative to succinic anhydride, the longer the carbon chain introduced by glutaric anhydride and / or adipic anhydride is, the greater the polarity difference with the perfluoropolyether molecule is, which can further improve the coating effect of the surfactant, thereby being more conducive to improving the stability of the perfluoropolyether-based magnetic liquid.

[0051] In some embodiments, the mass ratio of the pretreated perfluoropolyether surfactant to the nanomagnetic particles is 1:3 to 1:5. When the mass ratio is too low, it is not conducive to improving the coating effect on the nanomagnetic particles, thereby not being conducive to improving the stability of the perfluoropolyether-based magnetic liquid. When the mass ratio is too high, the coating effect on the nanomagnetic particles is not significantly improved, and since the perfluoropolyether surfactant is expensive, it is not conducive to reducing costs and increasing efficiency.

[0052] In some embodiments, the mass ratio of the nanomagnetic particles to the perfluoropolyether-based carrier liquid is 1:2 to 1:10. When the mass of the nanomagnetic particles is constant, the less perfluoropolyether-based carrier liquid is added, the better the magnetic properties of the magnetic liquid. Compared with perfluoropolyether surfactants, the pretreated perfluoropolyether surfactants have better adsorption and coating effects on nanomagnetic particles. Therefore, compared with the magnetic liquids in the related art, the magnetic liquids of the embodiments of the present invention can maintain good dispersibility and stability when the proportion of nanomagnetic particles is higher.

[0053] In addition, an embodiment of the present invention further provides a method for preparing a perfluoropolyether-based magnetic liquid, comprising the following steps:

[0054] S1. The perfluoropolyether surfactant is dissolved in a transition liquid, and then anhydride and a catalyst are added to the transition liquid, and the transition liquid is evaporated after the grafting reaction to obtain a pretreated perfluoropolyether surfactant;

[0055] S2. The nanomagnetic particles are dispersed in ultrapure water, and then the pretreated perfluoropolyether surfactant is added dropwise, and then the coated material is washed and dried to obtain coated nanomagnetic particles;

[0056] S3. Dispersing the coated nanomagnetic particles in a perfluoropolyether-based carrier liquid to obtain a perfluoropolyether-based magnetic liquid.

[0057] The preparation method of the embodiment of the present invention is to carry out a grafting reaction on the perfluoropolyether surfactant molecules, and introduce an active carbon chain at the end of the perfluoropolyether surfactant by using anhydride, so that the perfluoropolyether surfactant molecules after pretreatment contain a carbon chain-carboxyl structure at the end. This structure is quite different from the chemical properties of the fluorocarbon chain in the perfluoropolyether surfactant molecules, has a strong polarity, and is more compatible with water. In the subsequent coating process, it is not easy to be wrapped inside by the high molecular weight long chain of the perfluoropolyether surfactant, thereby improving the effect of contacting and reacting with the surface of the nanomagnetic particles. When preparing perfluoropolyether-based magnetic liquids, especially high molecular weight perfluoropolyether-based magnetic liquids, it has high dispersibility, thermal stability and magnetic properties, does not need to introduce non-magnetic substances to provide more adsorption sites, avoids the decline of magnetic properties, realizes the improvement of the high temperature resistance of the perfluoropolyether-based magnetic liquid, and improves the stability and reliability of the lubrication and sealing system.

[0058] In some embodiments, in step S1, the catalyst is 4-dimethylaminopyridine and / or triethylamine. Under the action of the organic alkaline catalyst, the alcoholic hydroxyl group or amine group at the end of the perfluoropolyether surfactant molecule can undergo an esterification reaction with the acid anhydride, so that the acid anhydride is open-loop grafted, and a carbon chain-carboxyl structure is introduced at the end of the perfluoropolyether surfactant molecule. This structure has a large difference in chemical properties from the fluorocarbon chain in the perfluoropolyether molecule, has a strong polarity, and is more compatible with water. In the subsequent coating process, it is not easy to be wrapped inside by the high molecular weight long chain of the perfluoropolyether surfactant, thereby improving the effect of the perfluoropolyether surfactant contacting and reacting with the surface of the nanomagnetic particles.

[0059] In some embodiments, in step S1, the temperature of the grafting reaction is 80-120°C, such as 80°C, 90°C, 100°C, 110°C, 120°C, etc., and the time of the grafting reaction is 6-12h, such as 6h, 7h, 8h, 9h, 10h, 11h, 12h, etc. Increasing the temperature of the reaction system can increase the solubility of the anhydride and the catalyst in the solvent, and improve the reaction speed and yield of the grafting reaction.

[0060] In some embodiments, in step S1, a perfluoropolyether surfactant is dissolved in a transition liquid, and then an excess of anhydride and catalyst are added to the transition liquid. After the grafting reaction, ultrapure water is used to dissolve and wash the residual anhydride and catalyst 3 to 5 times, and then the transition liquid is evaporated to obtain a pretreated perfluoropolyether surfactant. Adding an excessive amount of a reaction substrate (anhydride) that is less expensive and more readily available allows another expensive substrate (perfluoropolyether surfactant) to fully react, so that more pretreated surfactants can be obtained after purification and separation, which helps to reduce costs and increase efficiency. It should be understood that during the cleaning process, the oil layer containing the pretreated perfluoropolyether surfactant will be in the lower layer and the water layer will be in the upper layer. It is sufficient to clean until the upper water layer is neutral. Generally, cleaning 3 to 5 times can meet the requirements.

[0061] The preparation method of nanomagnetic particles needs to be designed according to the type of nanomagnetic particles. Taking Fe3O4 nanomagnetic particles as an example, the preparation method is as follows: FeCl3 solution and FeCl2·4H2O solution with a concentration of 0.3-0.4 mol / L are prepared. 3+ and Fe 2+ The molar ratio is 2:1 to 1:1 and added into a beaker. The temperature in the water bath is adjusted to 40 to 60°C and stirred. Excessive ammonia water is quickly added to fully precipitate the iron ions. The obtained Fe3O4 nano-magnetic particles are washed with ultrapure water.

[0062] In some embodiments, in step S2, the nanomagnetic particles are dispersed in ultrapure water, the temperature in the water bath is adjusted to 70-100°C and stirred, and then the pretreated perfluoropolyether surfactant is added dropwise, stirred at 300-1000 rpm for 15-30 min, and the coated material is washed and dried to obtain the coated nanomagnetic particles. Longer reaction temperature and stirring speed can improve the adsorption effect of the pretreated perfluoropolyether surfactant on the nanomagnetic particles in the water environment, and longer reaction time can increase the proportion of successfully coated nanomagnetic particles, but too high reaction temperature and too long reaction time may cause oxidation of the nanomagnetic particles, which is not conducive to improving magnetic properties.

[0063] In some embodiments, in step S3, the coated nano-magnetic particles are dispersed in the perfluoropolyether-based carrier liquid by ultrasonic dispersion treatment or high-speed ball milling treatment. The above treatments are helpful to improve the uniformity of dispersion.

[0064] The present invention is described in detail below with reference to the embodiments and the accompanying drawings.

[0065] Example 1: Preparation of Fe3O4 perfluoropolyether-based magnetic liquid

[0066] Step (1): Prepare 0.2 mol / L FeCl3 solution and FeCl2·4H2O solution according to Fe 3+ and Fe 2+ The molar ratio was 1.5:1 and added into a beaker to form a 300 mL solution. The temperature in the water bath was adjusted to 60 °C and stirred at 200 rpm. 30 mL of ammonia water was quickly added to fully precipitate the iron ions. The clear liquid and particles were separated by a magnet. The prepared Fe3O4 nanomagnetic particles were washed with ultrapure water several times, and the clear liquid was tested with pH test paper until the clear liquid was neutral.

[0067] Step (2) 2 g of a perfluoropolyether alcohol having a weight average molecular weight of 10,000 is dissolved in 50 mL of a transition solution, solid succinic anhydride and an equal amount of 4-dimethylaminopyridine are added to the solution at a molar ratio of 5:1 to the perfluoropolyether alcohol, the solution is heated to 100° C. and stirred until the solid is fully dissolved, and the stirring reaction is continued for 10 hours; three times the volume of ultrapure water is added to the solution and stirred continuously, and after standing and stratification, the water layer is removed by a separatory funnel, and the reaction is repeated 4 times until the pH value of the water layer is 7. The washed oil layer containing the perfluoropolyether alcohol is stirred in a water bath at 80° C. until the volume no longer decreases, and a pretreated perfluoropolyether surfactant is obtained.

[0068] Step (3) Disperse Fe3O4 nanoparticles in 300 mL of ultrapure water and transfer to a three-necked flask, stir in a water bath at 80°C, and continuously introduce nitrogen into the three-necked flask. After 5 minutes, increase the speed to 800 rpm, dropwise add the pretreated perfluoropolyether surfactant, and maintain the speed of 800 rpm for 30 minutes.

[0069] Step (4) uses a magnet to separate the liquid and particles, and uses ultrapure water to wash the coated Fe3O4 nanomagnetic particles three times until the conductivity of the clear liquid is σ≤100μs / cm. The nanomagnetic particles are placed in a vacuum drying oven to dry. The dried nanomagnetic particles are fully ground, and a perfluoropolyether-based carrier liquid with a weight average molecular weight of 10,000 is added at a mass ratio of 1:5 to the nanomagnetic particles, and ultrasonic treatment is performed for 2 hours to obtain a high-temperature resistant perfluoropolyether-based magnetic liquid with good stability.

[0070] Comparative Example 1: Preparation of Fe3O4 perfluoropolyether-based magnetic liquid

[0071] Step (1): Prepare 0.2 mol / L FeCl3 solution and FeCl2·4H2O solution, according to Fe 3+ and Fe 2+ The molar ratio was 1.5:1 and added into a beaker to form a 300 mL solution. The temperature in the water bath was adjusted to 60 °C and stirred at 200 rpm. 30 mL of ammonia water was quickly added to fully precipitate the iron ions. The clear liquid and particles were separated by a magnet. The prepared Fe3O4 nanomagnetic particles were washed with ultrapure water several times, and the clear liquid was tested with pH test paper until the clear liquid was neutral.

[0072] Step (2) Disperse Fe3O4 nanoparticles in 300 mL ultrapure water and transfer to a three-necked flask, stir in a water bath at 80°C, and continuously introduce nitrogen into the flask. After 5 minutes, increase the speed to 800 rpm, dropwise add 2 g of perfluoropolyether alcohol with a weight average molecular weight of 10,000, and maintain the speed of 800 rpm for 30 minutes.

[0073] Step (3) uses a magnet to separate the liquid and particles, and uses ultrapure water to wash the coated Fe3O4 nanomagnetic particles several times until the conductivity of the clear liquid is σ≤100μs / cm. The nanomagnetic particles are placed in a vacuum drying oven to dry. The dried nanomagnetic particles are fully ground, and a perfluoropolyether-based carrier liquid with a weight average molecular weight of 10,000 is added at a mass ratio of 1:5 to the nanomagnetic particles, and ultrasonic treatment is performed for 2 hours to obtain a perfluoropolyether-based magnetic liquid.

[0074] Example 2: Preparation of CoFe2O4 perfluoropolyether-based magnetic liquid

[0075] Step (1): Weigh 10.7 g of CoCl2·6H2O and 10.7 g of FeCl2·4H2O, dissolve in 400 mL of deionized water, and stir in a water bath at 45° C. for 10 min to make it uniform; weigh 30 g of concentrated ammonia water, add dropwise to the mixed salt solution, and keep heating and stirring for 40 min; after the reaction is completed, magnetically separate the nanomagnetic particles, wash the obtained Fe3O4 nanomagnetic particles with ultrapure water several times, and detect the clear liquid with pH test paper until the clear liquid is neutral.

[0076] Step (2) 4 g of a perfluoropolyetheramine with a weight average molecular weight of 15,000 was dissolved in 100 mL of a transition solution, solid glutaric anhydride and an equal amount of triethylamine were added to the solution at a molar ratio of 5:1 to the perfluoropolyetheramine, the solution was heated to 100° C. and stirred until the solid was fully dissolved, and the stirring reaction was continued for 10 hours; three times the volume of ultrapure water was added to the solution and stirred continuously, and after standing and stratification, the water layer was removed by a separatory funnel, and the process was repeated 4 times until the pH value of the water layer was 7. The washed oil layer containing the perfluoropolyetheramine was stirred in a water bath at 80° C. until the volume no longer decreased, and a pretreated perfluoropolyether surfactant was obtained.

[0077] Step (3) Disperse the CoFe2O4 nanoparticles in 400 mL of ultrapure water and transfer to a three-necked flask, stir in a water bath at 80°C, and continuously introduce nitrogen into the flask. After 5 minutes, increase the speed to 800 rpm, dropwise add the pretreated perfluoropolyether surfactant, and maintain the speed at 800 rpm for 30 minutes.

[0078] Step (4) uses a magnet to separate the liquid and particles, and uses ultrapure water to wash the coated CoFe2O4 nanomagnetic particles three times until the conductivity of the clear liquid is σ≤100μs / cm. The nanomagnetic particles are placed in a vacuum drying oven to dry. The dried nanomagnetic particles are fully ground, and a perfluoropolyether-based carrier liquid with a weight average molecular weight of 15,000 is added at a mass ratio of 1:4 to the nanomagnetic particles, and ultrasonic treatment is performed for 2 hours to obtain a stable high-temperature resistant perfluoropolyether-based magnetic liquid.

[0079] Comparative Example 2: Preparation of CoFe2O4 perfluoropolyether-based magnetic liquid

[0080] Step (1): Weigh 10.7 g of CoCl2·6H2O and 10.7 g of FeCl2·4H2O, dissolve in 400 mL of deionized water, and stir in a water bath at 45° C. for 10 min to make it uniform; weigh 30 g of concentrated ammonia water, add dropwise to the mixed salt solution, and keep heating and stirring for 40 min; after the reaction is completed, magnetically separate the nanomagnetic particles, wash the obtained Fe3O4 nanomagnetic particles with ultrapure water several times, and detect the clear liquid with pH test paper until the clear liquid is neutral.

[0081] Step (2) Disperse the CoFe2O4 nanoparticles in 400 mL of ultrapure water and transfer to a three-necked flask, stir in a water bath at 80°C, and continuously introduce nitrogen into the flask. After 5 minutes, increase the speed to 800 rpm, dropwise add 4 g of perfluoropolyetheramine with a weight average molecular weight of 15,000, and maintain the speed of 800 rpm for 30 minutes.

[0082] Step (3) uses a magnet to separate the liquid and particles, and uses ultrapure water to wash the coated CoFe2O4 nanomagnetic particles several times until the conductivity of the clear liquid is σ≤100μs / cm. The nanomagnetic particles are placed in a vacuum drying oven to dry. The dried nanomagnetic particles are fully ground, and a perfluoropolyether-based carrier liquid with a weight average molecular weight of 15,000 is added at a mass ratio of 1:4 to the nanomagnetic particles, and ultrasonic treatment is performed for 2 hours to obtain a perfluoropolyether-based magnetic liquid.

[0083] Embodiment three:

[0084] The preparation method of this embodiment is the same as that of the first embodiment, except that solid adipic anhydride is used instead of solid succinic anhydride.

[0085] Embodiment 4:

[0086] The preparation method of this embodiment is the same as that of the first embodiment, except that solid glutaric anhydride is used instead of solid succinic anhydride.

[0087] Performance Testing

[0088] (1) The saturation magnetization intensity of the perfluoropolyether-based magnetic liquids of the above embodiments and comparative examples was tested. The results are shown in Table 1 and Table 2. In addition, Figure 2 The magnetization curve of the perfluoropolyether-based magnetic liquid of Example 1 of the present invention is shown. Figure 3 The magnetization curve of the perfluoropolyether-based magnetic liquid of the second embodiment of the present invention is shown.

[0089] (2) The stability test was conducted on the perfluoropolyether-based magnetic liquids of Example 1, Example 2 and Comparative Example 1, Comparative Example 2. The perfluoropolyether-based magnetic liquids were heated and stirred at 200°C / 250°C for 5 hours, and then observed whether they were oxidized and turned red. The perfluoropolyether-based magnetic liquids were then placed on a φ80*100mm cylindrical N35 permanent magnet for 24 hours, and observed whether agglomeration and solid particle sedimentation occurred. The stability test results are shown in Table 1. In addition, Figure 4 The photo of the perfluoropolyether-based magnetic liquid of Example 1 after 24 hours of stability test is shown. Figure 5 The photo of the perfluoropolyether-based magnetic liquid of Example 2 after 24 hours of stability test is shown. Figure 6 A photograph of the perfluoropolyether-based magnetic liquid of Comparative Example 1 after 24 hours of stability testing is shown.

[0090] (3) The stability test was conducted on the perfluoropolyether-based magnetic liquids of Example 1, Example 3 and Example 4. The perfluoropolyether-based magnetic liquid was heated and stirred at 200°C for 5 hours to observe whether it was oxidized and turned red. The perfluoropolyether-based magnetic liquid was then placed on a φ80*100mm cylindrical N35 permanent magnet for 72 hours to observe whether agglomeration and solid particle sedimentation occurred and whether the spikes were blunted. The stability test results are shown in Table 2. In addition, Figure 7 The photo of the perfluoropolyether-based magnetic liquid of Example 1 after 72 hours of stability test is shown. Figure 8 The photo of the perfluoropolyether-based magnetic liquid of Example 3 after 72 hours of stability test is shown. Fig. 9 The photograph of the perfluoropolyether-based magnetic liquid of Example 4 after 72 hours of stability test is shown.

[0091] Table 1. Saturation magnetization and stability test results of perfluoropolyether-based magnetic liquids of Examples 1 and 2 and Comparative Examples 1 and 2

[0092]

[0093] Table 2. Saturation magnetization and stability test results of the perfluoropolyether-based magnetic liquids of Examples 3 and 4

[0094]

[0095] By comparing Example 1 with Comparative Example 1, and Example 2 with Comparative Example 2 in Table 1, it can be seen that the perfluoropolyether-based magnetic liquid of the embodiment of the present invention is more stable than the perfluoropolyether-based magnetic liquid of the comparative example. This is because it is difficult for the polymer perfluoropolyether surfactant to form a sufficiently stable coating on the surface of the nanomagnetic particles, resulting in poor antioxidant capacity of the magnetic liquid and poor suspension stability of the nanomagnetic particles. The embodiment of the present invention uses a pretreated perfluoropolyether surfactant instead of a perfluoropolyether surfactant, and the pretreated perfluoropolyether surfactant can form a sufficiently stable coating on the surface of the nanomagnetic particles, thereby enhancing the antioxidant capacity of the magnetic liquid and improving the suspension stability of the nanomagnetic particles.

[0096] By comparing Example 1 with Example 3 and Example 4 in Table 2, after the perfluoropolyether-based magnetic liquid of Example 1 was placed on the magnet for 72 hours, the spikes were obviously blunted into wrinkles (see Figure 7 ), indicating that the concentration of the top layer changes greatly, while the spikes of the perfluoropolyether-based magnetic liquid of Example 3 can still remain sharp after being placed on the magnet for 72 hours, indicating that the stability of the perfluoropolyether-based magnetic liquids of Examples 3 and 4 is better than that of Example 1. This is because the longer the carbon chain introduced by glutaric anhydride and / or adipic anhydride relative to succinic anhydride, the greater the polarity difference with the perfluoropolyether molecule, which can further improve the coating effect of the surfactant, thereby being more conducive to improving the stability of the perfluoropolyether-based magnetic liquid.

[0097] 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.

[0098] 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 nano magnetic particles, a pretreated perfluoropolyether surfactant and a perfluoropolyether-based carrier liquid. The pretreated perfluoropolyether surfactant is prepared by grafting the perfluoropolyether surfactant with anhydride.

2. The perfluoropolyether-based magnetic liquid according to claim 1, characterized in that: The perfluoropolyether surfactant is perfluoropolyether alcohol and / or perfluoropolyether amine; and / or the weight average molecular weight of the perfluoropolyether surfactant is 5000-20000; and / or the weight average molecular weight of the perfluoropolyether-based carrier liquid is 5000-20000.

3. The perfluoropolyether-based magnetic liquid according to claim 1, characterized in that: The nano magnetic particles are at least one of Fe3O4, γ-Fe2O3 and CoFe2O4.

4. The perfluoropolyether-based magnetic liquid according to claim 1, characterized in that: The acid anhydride is at least one of succinic anhydride, glutaric anhydride and adipic anhydride.

5. The perfluoropolyether-based magnetic liquid according to claim 1, characterized in that: The mass ratio of the pretreated perfluoropolyether surfactant to the nanomagnetic particles is 1:3 to 1:5; and / or the mass ratio of the nanomagnetic particles to the perfluoropolyether-based carrier liquid is 1:2 to 1:

10.

6. The method for preparing a perfluoropolyether-based magnetic liquid according to any one of claims 1 to 5, characterized in that: The following steps are involved: S1. The perfluoropolyether surfactant is dissolved in a transition liquid, and then anhydride and a catalyst are added to the transition liquid, and the transition liquid is evaporated after the grafting reaction to obtain a pretreated perfluoropolyether surfactant; S2. The nanomagnetic particles are dispersed in ultrapure water, and then the pretreated perfluoropolyether surfactant is added dropwise, and then the coated material is washed and dried to obtain coated nanomagnetic particles; S3. Dispersing the coated nanomagnetic particles in a perfluoropolyether-based carrier liquid to obtain a perfluoropolyether-based magnetic liquid.

7. The preparation method according to claim 6, characterized in that: In step S1, the catalyst is 4-dimethylaminopyridine and / or triethylamine.

8. The preparation method according to claim 6, characterized in that: In step S1, the temperature of the grafting reaction is 80-120° C., and the time of the grafting reaction is 6-12 hours.

9. The preparation method according to claim 6, characterized in that: In step S1, a perfluoropolyether surfactant is dissolved in a transition liquid, and then an excess of anhydride and a catalyst are added to the transition liquid. After the grafting reaction, ultrapure water is used to dissolve and wash the residual anhydride and catalyst for 3 to 5 times, and then the transition liquid is evaporated to obtain a pretreated perfluoropolyether surfactant.

10. The preparation method according to claim 6, characterized in that: In step S2, the nanomagnetic particles are dispersed in ultrapure water, the temperature in the water bath is adjusted to 70-100° C. and stirred, then the pretreated perfluoropolyether surfactant is added dropwise, stirred at a speed of 300-1000 rpm for 15-30 min, the coated material is washed and dried to obtain the coated nanomagnetic particles.

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