A perfluoropolyether-based magnetic liquid and a method for preparing the same

Abstract

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

Description

TECHNICAL FIELD

[0001] The application belongs to the technical field of magnetic liquids, and particularly relates to a perfluoropolyether-based magnetic liquid and a preparation method thereof. BACKGROUND

[0002] A magnetic liquid is a new type of composite nanomaterial. By uniformly dispersing magnetic particles with a diameter in the nanometer range in a base carrier liquid after modification by a suitable surfactant, a stable colloidal system is formed. This material has both the fluidity of a liquid and magnetism, and can be used for lubrication, manufacturing of magnetic liquid sealing devices, sensors and shock absorbers, and has a wide range of applications in many high-tech fields such as aerospace, electronics, mechanization, energy metallurgy, instruments and meters, and biomedicine. The magnetic liquid relies on a surfactant to achieve stable suspension of the nanometer magnetic particles in a liquid environment. The surfactant molecules need to provide sufficient repulsive force to prevent the nanometer magnetic particles from agglomerating together under the action of gravity, inter-particle magnetic force or van der Waals force.

[0003] In existing magnetic liquid preparation technologies, ester and diester oils, mineral oils and water are common base carrier liquids for magnetic liquids. However, due to the physical and chemical properties of these substances, they will produce a large amount of volatilization or molecular thermal decomposition at high temperatures. The loss or denaturation of the base carrier liquid will cause the magnetic liquid to separate into solid particles and liquid, ultimately resulting in the magnetic liquid being unable to be reused. Perfluoropolyether is a special colorless, odorless and transparent liquid perfluorinated compound with a structure similar to that of long-chain hydrocarbon polymers, but with H atoms replaced by F atoms in the molecular chain. Due to the high strength and stability of the C-F 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-combustibility, high thermal stability and stable chemical properties. When used as a base carrier liquid for a magnetic liquid, it can effectively improve the performance of the magnetic liquid in a high-temperature environment, and has 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 depending on the monomers and the synthesis method. According to the molecular structure of the perfluoropolyether, it can be divided into K-type, Y-type, Z-type and D-type perfluoropolyethers, with a weight average molecular weight of about 1000-20000. The higher the molecular weight of the perfluoropolyether, the lower the volatilization rate and the higher the thermal stability. In order to enable the magnetic liquid to work normally in a high-temperature environment, a high molecular weight perfluoropolyether base carrier liquid and a corresponding high molecular weight perfluoropolyether surfactant need to be used.

[0004] However, since the reaction and adsorption of perfluoropolyether surfactant molecules, such as perfluoropolyether carboxylic acid or perfluoropolyether amine, with nano-magnetic particles is achieved by relying on single active groups at the end, when the molecular weight is high, the flexibility of the polyether chain can cause the surfactant molecules to curl and agglomerate, reducing the probability of contact between the end group active group and the surface of the nano-magnetic particle, and increasing the difficulty of the surface modification reaction of the surfactant, so it is difficult to obtain a long-term stable high-temperature resistant perfluoropolyether-based magnetic liquid. For example, patent application file CN201310692408.5 discloses a preparation method of a perfluoropolyether oil-based magnetic liquid. The magnetic liquid is prepared from bare Fe3O4 magnetic nanoparticles, perfluoropolyether carboxylic acid surfactant, and perfluoropolyether oil-based carrier liquid. First, bare Fe3O4 nanoparticles with an average particle size of 10 nm are prepared by chemical co-precipitation; then perfluoropolyether carboxylic acid surfactant is used for modification; finally, high-energy ball milling or ultrasonic oscillation method is used to blend the modified Fe3O4 magnetic nanoparticles with perfluoropolyether oil-based carrier liquid to form a perfluoropolyether oil-based magnetic liquid. Among them, perfluoropolyether carboxylic acid is used as a surfactant, and perfluoropolyether carboxylic acid surfactant is directly added to the aqueous solution during preparation to react with the magnetic nanoparticles. However, as the molecular weight increases, the dispersibility and reactivity of perfluoropolyether carboxylic acid in the aqueous phase will 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 related technologies, but their magnetic properties are relatively low. For example, patent application file CN202210777827.8 discloses a low-temperature resistant perfluoropolyether-based magnetic liquid and a preparation method thereof. The perfluoropolyether-based magnetic liquid is prepared from graphene oxide-coated magnetic nanoparticles, a surfactant, and a base carrier liquid. The surfactant is a perfluoroalkyl amine, a perfluoropolyether carboxylic acid, or a mixture thereof. The base carrier liquid is a perfluoropolyether oil. The preparation method of the perfluoropolyether-based magnetic liquid uses a surfactant to coat and modify the graphene oxide-coated magnetic nanoparticles to obtain modified graphene oxide-coated magnetic nanoparticles, which are then dispersed in a perfluoropolyether oil-based carrier liquid to prepare a perfluoropolyether-based magnetic liquid. Although this method uses graphene oxide to pre-modify the magnetic nanoparticles, providing more adsorption sites and thus improving the reactivity of the subsequent surfactant, ultimately improving the stability of the perfluoropolyether-based magnetic liquid. However, this method introduces non-magnetic solid substances, which reduces the magnetic properties of the magnetic liquid and thus affects the performance. SUMMARY

[0006] The present application aims to at least partially solve one of the technical problems in the related art. To this end, embodiments of the present application provide a perfluoropolyether-based magnetic liquid and a preparation method thereof, the perfluoropolyether-based magnetic liquid having high colloidal stability and thermal stability and being capable of being applied to long-term stable operation under high-temperature working conditions.

[0007] Embodiments of the present application provide a perfluoropolyether-based magnetic liquid, comprising nano-magnetic particles, pretreated perfluoropolyether surfactant and perfluoropolyether-based carrier liquid, wherein the pretreated perfluoropolyether surfactant is prepared by grafting reaction of perfluoropolyether surfactant and anhydride.

[0008] The perfluoropolyether-based magnetic liquid according to embodiments of the present application has the following advantages and technical effects:

[0009] The pretreated perfluoropolyether surfactant is obtained by introducing an active carbon chain into the end group of the perfluoropolyether surfactant, and has better dispersibility in an aqueous environment and better reactivity with the nano-magnetic particles than the perfluoropolyether surfactant, so that the nano-magnetic particles can be more stably dispersed in the perfluoropolyether-based carrier liquid. Therefore, compared with the perfluoropolyether-based magnetic liquid in the related art, the perfluoropolyether-based magnetic liquid according to embodiments of the present application has higher colloidal stability and thermal stability, and can be applied to long-term stable operation under high-temperature working conditions.

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

[0011] In some embodiments, the perfluoropolyether surfactant has a weight average molecular weight of 5000-20000.

[0012] In some embodiments, the perfluoropolyether surfactant has a weight average molecular weight of 10000-20000.

[0013] In some embodiments, the perfluoropolyether-based carrier liquid has a weight average molecular weight of 5000-20000.

[0014] In some embodiments, the perfluoropolyether-based carrier liquid has a weight average molecular weight of 10000-20000.

[0015] In some embodiments, the nano-magnetic 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 nano-magnetic particles is 1:3-1:5.

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

[0019] In addition, the embodiment of the present application further provides a preparation method of the perfluoropolyether-based magnetic liquid, comprising the following steps:

[0020] S1. Dissolving the perfluoropolyether surfactant in a transition liquid, then adding anhydride and a catalyst to the transition liquid, evaporating the transition liquid after grafting reaction to obtain the pretreated perfluoropolyether surfactant;

[0021] S2. Dispersing the nanometer magnetic particles in ultrapure water, then adding the pretreated perfluoropolyether surfactant dropwise, then washing and drying the coated substance to obtain the coated nanometer magnetic particles;

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

[0023] The preparation method of the embodiment of the present application has the following advantages and technical effects:

[0024] The preparation method of the embodiment of the present application performs grafting reaction on the perfluoropolyether surfactant molecules, introduces active carbon chains at the end groups of the perfluoropolyether surfactant by using anhydride, improves the dispersibility of the perfluoropolyether surfactant in the aqueous phase environment and the reactivity with the nanometer magnetic particles, makes the nanometer magnetic particles more stable in the perfluoropolyether-based carrier liquid, and thus improves the colloidal stability and thermal stability of the magnetic liquid, which can be applied to long-term stable operation under high-temperature working 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℃, and the time of the grafting reaction is 6-12h.

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

[0028] In some embodiments, in step S2, the nano-magnetic particles are dispersed in ultrapure water, the temperature in the water bath is adjusted to 70-100℃ and stirring is performed, then the pretreated perfluoropolyether surfactant is added dropwise, stirring is performed at a speed of 300-1000 rpm for 15-30 min, the coated substance is washed and dried, and the coated nano-magnetic particles are obtained. BRIEF DESCRIPTION OF DRAWINGS

[0029] Figure 1 is a structural formula of the pretreated perfluoropolyether surfactant in the perfluoropolyether-based magnetic liquid according to an embodiment of the present application.

[0030] Figure 2 is a magnetization curve of the perfluoropolyether-based magnetic liquid according to embodiment one.

[0031] Figure 3 is a magnetization curve of the perfluoropolyether-based magnetic liquid according to embodiment two.

[0032] Figure 4 is a photo of the perfluoropolyether-based magnetic liquid according to embodiment one after a stability test for 24 h.

[0033] Figure 5 is a photo of the perfluoropolyether-based magnetic liquid according to embodiment two after a stability test for 24 h.

[0034] Figure 6 is a photo of the perfluoropolyether-based magnetic liquid according to comparative example one after a stability test for 24 h.

[0035] Figure 7 is a photo of the perfluoropolyether-based magnetic liquid according to embodiment one after a stability test for 72 h.

[0036] Figure 8 is a photo of the perfluoropolyether-based magnetic liquid according to embodiment three after a stability test for 72 h.

[0037] Figure 9 is a photo of the perfluoropolyether-based magnetic liquid according to embodiment four after a stability test for 72 h. DETAILED DESCRIPTION

[0038] Embodiments of the present application are described in detail below, examples of which are shown in the accompanying drawings. The embodiments described below with reference to the accompanying drawings are exemplary and are intended to explain the present application, and cannot be understood as limiting the present application.

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

[0040] The end group of the perfluoropolyether surfactant is introduced into an active carbon chain to obtain the pretreated perfluoropolyether surfactant, which has better dispersibility in an aqueous phase environment and better reactivity with the nanometer magnetic particles than the perfluoropolyether surfactant, and can make the nanometer magnetic particles more stably dispersed in the perfluoropolyether-based carrier liquid. Therefore, compared with the perfluoropolyether-based magnetic liquid in the related art, the colloidal stability and thermal stability of the perfluoropolyether-based magnetic liquid in the embodiment of the present application are higher, so that the perfluoropolyether-based magnetic liquid in the embodiment of the present application can be applied to long-term stable operation under high-temperature working conditions.

[0041] In some embodiments, the magnetic liquid in the embodiment of the present application does not include non-magnetic solid substances. Avoiding the addition of non-magnetic solid substances can make the magnetic liquid maintain higher magnetic properties.

[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 perfluoropolyether amine is as follows:

[0046]

[0047] In some embodiments, the weight average molecular weight of the perfluoropolyether surfactant is 5000-20000, preferably 10000-20000. The higher the molecular weight of the perfluoropolyether surfactant, the lower the volatility and the higher the thermal stability. Due to the presence of the pretreated perfluoropolyether surfactant, even if a high-molecular-weight perfluoropolyether surfactant is used, the high-molecular-weight perfluoropolyether surfactant can have stronger interaction with the surface of the nanometer magnetic particles, thereby improving the adsorption and coating effect of the surfactant without reducing the magnetic properties of the nanometer magnetic particles by introducing non-magnetic substances.

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

[0049] In some embodiments, the nanometer magnetic particles are at least one of Fe3O4, γ-Fe2O3 and CoFe2O4. The above-mentioned nanometer magnetic 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 acid anhydride can introduce an active carbon chain at the end of the perfluoropolyether surfactant. Preferably, the acid anhydride is glutaric anhydride and / or adipic anhydride. As shown in the formula, compared with succinic anhydride, the longer the carbon chain introduced by glutaric anhydride and / or adipic anhydride, the greater the difference in polarity with the perfluoropolyether molecule, and the better the coating effect of the surfactant, thereby more conducive to improving the stability of the perfluoropolyether-based magnetic liquid. Figure 1

[0051] In some embodiments, the mass ratio of the pretreated perfluoropolyether surfactant to the nanometer magnetic particles is 1:3-1:5. When the mass ratio is too low, it is not conducive to improving the coating effect on the nanometer magnetic particles, thereby not conducive to improving the stability of the perfluoropolyether-based magnetic liquid. When the mass ratio is too high, the coating effect on the nanometer magnetic particles is not significantly improved, and at the same time, due to the high price of the perfluoropolyether surfactant, it is not conducive to cost reduction and efficiency improvement.

[0052] In some embodiments, the mass ratio of the nanometer magnetic particles to the perfluoropolyether-based carrier liquid is 1:2-1:10. Under the condition that the mass of the nanometer magnetic particles is certain, the less the perfluoropolyether-based carrier liquid added, the better the magnetic properties of the magnetic liquid. Compared with the perfluoropolyether surfactant, the pretreated perfluoropolyether surfactant has better adsorption and coating effect on the nanometer magnetic particles, and therefore, compared with the magnetic liquid in the related art, the magnetic liquid of the embodiments of the present application can maintain good dispersibility and stability at a higher proportion of nanometer magnetic particles.

[0053] In addition, the embodiments of the present application also provide a preparation method of a perfluoropolyether-based magnetic liquid, comprising the following steps:

[0054] S1. Dissolve the perfluoropolyether surfactant in a transition liquid, then add an acid anhydride and a catalyst to the transition liquid, evaporate the transition liquid after grafting reaction, and obtain a pretreated perfluoropolyether surfactant;

[0055] S2. Disperse the nanometer magnetic particles in ultrapure water, then drop the pretreated perfluoropolyether surfactant, then wash and dry the coated substance, and obtain the coated nanometer magnetic particles;

[0056] S3. Disperse the coated nanometer magnetic particles in a perfluoropolyether-based carrier liquid, and obtain a perfluoropolyether-based magnetic liquid.

[0057] ​The preparation method of the embodiment of the present application introduces an active carbon chain at the end of the perfluoropolyether surfactant by grafting reaction, and the perfluoropolyether surfactant molecule contains a carbon chain-carboxyl structure at the end after pretreatment. The structure is quite different from the chemical properties of the fluorocarbon chain in the perfluoropolyether surfactant molecule, has strong polarity, has higher compatibility with water, is not easily wrapped inside by the high molecular weight long chain of the perfluoropolyether surfactant in the subsequent coating process, improves the effect of contacting and reacting with the surface of the nano magnetic particles, has high dispersibility, thermal stability and magnetic performance when preparing the perfluoropolyether-based magnetic liquid, especially the high molecular weight perfluoropolyether-based magnetic liquid, does not need to introduce non-magnetic substances to provide more adsorption sites, avoids the decline of the magnetic performance, 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 alcohol hydroxyl or amine group at the end of the perfluoropolyether surfactant molecule can undergo esterification with the acid anhydride, so that the acid anhydride is ring-opening grafted, and a carbon chain-carboxyl structure is introduced at the end of the perfluoropolyether surfactant. The structure is quite different from the chemical properties of the fluorocarbon chain in the perfluoropolyether molecule, has strong polarity, has higher compatibility with water, is not easily wrapped inside by the high molecular weight long chain of the perfluoropolyether surfactant in the subsequent coating process, and improves the effect of contacting and reacting with the surface of the nano magnetic particles.

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

[0060] In some embodiments, in step S1, the perfluoropolyether surfactant is dissolved in the transition liquid, and then excess acid anhydride and catalyst are added to the transition liquid. After the grafting reaction, the residual acid anhydride and catalyst are dissolved and washed with ultrapure water for 3-5 times, and then the transition liquid is evaporated to dryness to obtain the pretreated perfluoropolyether surfactant. Excess reaction substrate (acid anhydride) with lower price and more availability is added, so that the other expensive substrate (perfluoropolyether surfactant) is fully reacted, which can make more pretreated surfactants obtained after purification and separation, and help to reduce cost and increase efficiency. It should be understood that in the washing process, the oil layer containing the pretreated perfluoropolyether surfactant is in the lower layer, and the water layer is in the upper layer. The washing is completed when the upper water layer is neutral, and generally 3-5 times of washing can meet the requirements.

[0061] The preparation method of the nano-magnetic particles needs to be designed according to the type of the nano-magnetic particles. Taking Fe3O4nano-magnetic particles as an example, a solution of FeCl3with a concentration of 0.3-0.4 mol / L and a solution of FeCl2·4H2O are prepared, and the molar ratio of Fe 3+ and Fe 2+ is 2:1-1:1, and the temperature of the water bath is adjusted to 40-60°C and stirring is performed. Excess ammonia water is rapidly added to fully precipitate the iron ions, and the prepared Fe3O4nano-magnetic particles are washed with ultrapure water.

[0062] In some embodiments, in step S2, the nano-magnetic particles are dispersed in ultrapure water, the temperature of the water bath is adjusted to 70-100°C and stirring is performed, then the pretreated perfluoropolyether surfactant is added dropwise, and stirring is performed at a speed of 300-1000 rpm for 15-30 min. The coated nano-magnetic particles are obtained by washing and drying the coated substance. Longer reaction temperature and stirring speed can improve the adsorption effect of the pretreated perfluoropolyether surfactant on the nano-magnetic particles in the water environment, and longer reaction time can improve the proportion of successfully coated nano-magnetic particles. However, too high reaction temperature and too long reaction time may cause oxidation of the nano-magnetic particles, which is not conducive to improving the 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 treatment helps to improve the uniformity of dispersion.

[0064] The present application will be described in detail below with reference to the embodiments and the accompanying drawings.

[0065] Example 1: Preparation of Fe3O4perfluoropolyether-based magnetic liquid

[0066] Step (1): A solution of FeCl3with a concentration of 0.2 mol / L and a solution of FeCl2·4H2O are prepared, and the molar ratio of Fe 3+ and Fe 2+ is 1.5:1, and 300 mL of solution is formed. The temperature of the water bath is adjusted to 60°C and stirring is performed at 200 rpm. 30 mL of ammonia water is rapidly added to fully precipitate the iron ions. The supernatant and particles are separated using a magnet, and the prepared Fe3O4nano-magnetic particles are washed several times with ultrapure water. The supernatant is detected using pH paper, and the washing is continued until the supernatant is neutral.

[0067] Step (2) 2 g of perfluoropolyether alcohol with a weight average molecular weight of 10000 was dissolved in 50 mL of transition liquid, solid succinic anhydride and an equal amount of 4-dimethylamino pyridine in a molar ratio of 5:1 to the perfluoropolyether alcohol were added to the solution, the solution was heated to 100°C and stirred until the solid was fully dissolved, and the stirring reaction was continued for 10 h; three times the volume of ultrapure water was added to the solution and stirring was continued, after standing and layering, 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 oil layer containing the perfluoropolyether alcohol after washing was stirred in a water bath at 80°C until the volume no longer decreased, and a pretreated perfluoropolyether surfactant was obtained.

[0068] Step (3) Fe3O4 nano-magnetic particles were dispersed in 300 mL of ultrapure water and transferred to a three-necked flask, stirred in a water bath at 80°C, and nitrogen was continuously introduced into the three-necked flask. After 5 min, the stirring speed was increased to 800 rpm, and the pretreated perfluoropolyether surfactant was added dropwise, and the stirring reaction was continued for 30 min at a stirring speed of 800 rpm.

[0069] Step (4) The liquid and particles were separated using a magnet, and the coated Fe3O4 nano-magnetic particles were washed 3 times with ultrapure water until the conductivity σ of the supernatant was ≤100 μs / cm. The nano-magnetic particles were dried in a vacuum drying oven. The dried nano-magnetic particles were thoroughly ground, and a perfluoropolyether-based carrier liquid with a weight average molecular weight of 10000 was added in a mass ratio of 1:5 to the nano-magnetic particles, and ultrasonic treatment was performed for 2 h, thereby obtaining a high-temperature-resistant perfluoropolyether-based magnetic liquid with good stability.

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

[0071] Step (1): FeCl3 solution and FeCl2·4H2O solution with a concentration of 0.2 mol / L were prepared, and FeCl3 and FeCl2·4H2O were added to a beaker in a molar ratio of 1.5:1, forming a 300 mL solution, the temperature of the water bath was adjusted to 60°C and stirring was performed at 200 rpm, 30 mL of ammonia water was quickly added, and the iron ions were fully precipitated, the supernatant and particles were separated using a magnet, and the prepared Fe3O4 nano-magnetic particles were washed several times with ultrapure water, and the supernatant was detected using pH paper, and the washing was continued until the supernatant was neutral. 3+ and Fe 2+ were added to a beaker in a molar ratio of 1.5:1, forming a 300 mL solution, the temperature of the water bath was adjusted to 60°C and stirring was performed at 200 rpm, 30 mL of ammonia water was quickly added, and the iron ions were fully precipitated, the supernatant and particles were separated using a magnet, and the prepared Fe3O4 nano-magnetic particles were washed several times with ultrapure water, and the supernatant was detected using pH paper, and the washing was continued until the supernatant was neutral.

[0072] Step (2) Fe3O4 nano-magnetic particles were dispersed in 300 mL of ultrapure water and transferred to a three-necked flask, stirred in a water bath at 80°C, and nitrogen was continuously introduced into the three-necked flask. After 5 min, the stirring speed was increased to 800 rpm, and 2 g of perfluoropolyether alcohol with a weight average molecular weight of 10000 was added dropwise, and the stirring reaction was continued for 30 min at a stirring speed of 800 rpm.

[0073] Step (3) separates the liquid and particles using a magnet, and washes the coated Fe3O4nanoparticle several times with ultrapure water until the conductivity of the supernatant is less than or equal to 100 μs / cm. The nanoparticle is dried in a vacuum drying oven. The dried nanoparticle is ground thoroughly, and a perfluoropolyether-based carrier liquid with a weight average molecular weight of 10,000 is added in a mass ratio of 1:5 to the nanoparticle. The mixture is ultrasonically treated for 2 h to obtain a perfluoropolyether-based magnetic liquid.

[0074] Example Two: Preparation of a CoFe2O4perfluoropolyether-based magnetic liquid

[0075] Step (1): 10.7 g of CoCl2·6H2O and 10.7 g of FeCl2·4H2O are weighed and dissolved in 400 mL of deionized water, which is stirred in a water bath at 45°C for 10 min to make it uniform. 30 g of concentrated ammonia is added dropwise to the mixed salt solution while maintaining heating and stirring for 40 min. After the reaction is complete, the nanoparticle is separated by a magnet, and the prepared Fe3O4nanoparticle is washed several times with ultrapure water, and the supernatant is detected with pH paper until the supernatant is neutral.

[0076] Step (2) 4 g of perfluoropolyether amine with a weight average molecular weight of 15,000 is dissolved in 100 mL of transition liquid, and solid glutaric anhydride and an equal amount of triethylamine are added to the solution in a molar ratio of 5:1 to the perfluoropolyether amine. The solution is heated to 100°C and stirred until the solid is fully dissolved. The stirring is continued for 10 h. Three times the volume of ultrapure water is added to the solution and stirring is continued. After the layers are separated by standing, the water layer is removed by a separatory funnel, and the process is repeated 4 times until the pH value of the water layer is 7. The oil layer containing the perfluoropolyether amine after washing is stirred in a water bath at 80°C until the volume no longer decreases, and a pretreated perfluoropolyether surfactant is obtained.

[0077] Step (3) disperses the CoFe2O4nanoparticle in 400 mL of ultrapure water and transfers it to a three-necked flask. The flask is stirred in a water bath at 80°C, and nitrogen is continuously introduced into the flask. After 5 min, the stirring speed is increased to 800 rpm, and the pretreated perfluoropolyether surfactant is added dropwise. The stirring speed is maintained at 800 rpm for 30 min.

[0078] Step (4) separates the liquid and particles using a magnet, and washes the coated CoFe2O4nanoparticle 3 times with ultrapure water until the conductivity of the supernatant is less than or equal to 100 μs / cm. The nanoparticle is dried in a vacuum drying oven. The dried nanoparticle is ground thoroughly, and a perfluoropolyether-based carrier liquid with a weight average molecular weight of 15,000 is added in a mass ratio of 1:4 to the nanoparticle. The mixture is ultrasonically treated for 2 h to obtain a stable high-temperature-resistant perfluoropolyether-based magnetic liquid.

[0079] Preparation of CoFe2O4 perfluoropolyether-based magnetic liquid

[0080] Step (1): 10.7 g of CoCl2·6H2O and 10.7 g of FeCl2·4H2O were weighed and dissolved in 400 mL of deionized water, and stirred at 45°C in a water bath for 10 min to make them uniform; 30 g of concentrated ammonia was added dropwise into the mixed salt solution while keeping heating and stirring for 40 min; after the reaction was completed, the nano magnetic particles were separated by magnetism, and the prepared Fe3O4 nano magnetic particles were washed several times with ultrapure water, and the supernatant was detected with pH paper until the supernatant was neutral.

[0081] Step (2) The CoFe2O4 nano magnetic particles were dispersed in 400 mL of ultrapure water and transferred to a three-necked flask, and stirred at 80°C in a water bath, and nitrogen was continuously introduced into the flask. 5 min later, the stirring speed was increased to 800 rpm, and 4 g of perfluoropolyether amine with a weight average molecular weight of 15000 was added dropwise, and the stirring speed was maintained at 800 rpm for 30 min.

[0082] Step (3) The liquid and particles were separated using a magnet, and the coated CoFe2O4 nano magnetic particles were washed several times with ultrapure water until the conductivity σ of the supernatant was ≤100 μs / cm. The nano magnetic particles were dried in a vacuum drying oven. The dried nano magnetic particles were ground thoroughly, and 4 g of perfluoropolyether-based carrier liquid with a weight average molecular weight of 15000 was added, and ultrasonic treatment was performed for 2 h to obtain a perfluoropolyether-based magnetic liquid.

[0083] Example Three:

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

[0085] Example Four:

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

[0087] Performance test

[0088] (1) The saturation magnetization of the perfluoropolyether-based magnetic liquid of each of the above examples and the comparative example was tested, and the results are shown in Table 1 and Table 2, and in addition, Figure 2 The magnetization curve of the perfluoropolyether-based magnetic liquid of Example One of the present application is shown, Figure 3 The magnetization curve of the perfluoropolyether-based magnetic liquid of Example Two of the present application is shown.

[0089] (2) Stability tests were performed on the perfluoropolyether-based magnetic liquids of Example 1, Example 2, and Comparative Example 1 and Comparative Example 2. The perfluoropolyether-based magnetic liquids were first heated and stirred at 200°C / 250°C for 5 hours, and then observed for redox changes. The perfluoropolyether-based magnetic liquids were then placed on a cylindrical N35 permanent magnet with a diameter of 80 mm and a height of 100 mm for 24 hours, and then observed for agglomeration and solid particle sedimentation. The stability test results are shown in Table 1, and in addition, Figure 4 A photograph of the perfluoropolyether-based magnetic liquid of Example 1 after 24 hours of stability testing is shown, Figure 5 A photograph of the perfluoropolyether-based magnetic liquid of Example 2 after 24 hours of stability testing 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) Stability tests were performed on the perfluoropolyether-based magnetic liquids of Example 1, Example 3, and Example 4. The perfluoropolyether-based magnetic liquids were first heated and stirred at 200°C for 5 hours, and then observed for redox changes. The perfluoropolyether-based magnetic liquids were then placed on a cylindrical N35 permanent magnet with a diameter of 80 mm and a height of 100 mm for 72 hours, and then observed for agglomeration, solid particle sedimentation, and whether the spikes were blunted. The stability test results are shown in Table 2, and in addition, Figure 7 A photograph of the perfluoropolyether-based magnetic liquid of Example 1 after 72 hours of stability testing is shown, Figure 8 A photograph of the perfluoropolyether-based magnetic liquid of Example 3 after 72 hours of stability testing is shown, Figure 9 A photograph of the perfluoropolyether-based magnetic liquid of Example 4 after 72 hours of stability testing is shown.

[0091] Table 1. Saturation magnetization and stability test results of the 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 and Comparative Example 1 in Table 1, and comparing Example 2 and Comparative Example 2, it can be seen that the perfluoropolyether-based magnetic liquid of the present application has better stability than the perfluoropolyether-based magnetic liquid of the comparative example. This is because the high molecular perfluoropolyether surfactant is difficult to form a fully stable coating on the surface of the nano magnetic particles, resulting in poor oxidation resistance of the magnetic liquid and poor suspension stability of the nano magnetic particles. The perfluoropolyether surfactant used in the present application is pretreated, which can form a fully stable coating on the surface of the nano magnetic particles, thereby enhancing the oxidation resistance of the magnetic liquid and improving the suspension stability of the nano magnetic particles.

[0096] By comparing Example 1 and Example 3, and Example 4 in Table 2, the perfluoropolyether-based magnetic liquid of Example 1 is obviously passivated into a wrinkle shape after being placed on a magnet for 72 hours (see Figure 7 ), indicating that the concentration of the top layer changes greatly, while the perfluoropolyether-based magnetic liquid of Example 3 can still maintain sharpness after being placed on a magnet for 72 hours, indicating that the stability of the perfluoropolyether-based magnetic liquid of Example 3 and Example 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 difference in polarity with the perfluoropolyether molecule, which can improve the coating effect of the surfactant, thereby improving the stability of the perfluoropolyether-based magnetic liquid.

[0097] In the present application, the terms "one embodiment", "some embodiments", "example", "specific example", or "some examples" and the like mean that the specific features, structures, materials or characteristics described in connection with the embodiment or example are included in at least one embodiment or example of the present application. In the present specification, the illustrative expressions of the above terms do not necessarily refer to the same embodiment or example. Moreover, the specific features, structures, materials or characteristics described can be combined in any appropriate manner in any one or more embodiments or examples. In addition, different embodiments or examples described in the present specification and the features of different embodiments or examples can be combined and combined by those skilled in the art without contradiction.

[0098] Although the embodiments of the present application have been shown and described above, it should be understood that the above embodiments are exemplary and should not be construed as limiting the present application, and those skilled in the art can make changes, modifications, replacements and variations to the above embodiments within the scope of the present application.

Claims

1. A perfluoropolyether-based magnetic liquid, characterized in that, The nanometer magnetic particle, the pretreated perfluoropolyether surfactant and the perfluoropolyether-based carrier liquid, the pretreated perfluoropolyether surfactant is prepared by grafting reaction of perfluoropolyether surfactant and anhydride, the anhydride is adipic anhydride; 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.

2. The perfluoropolyether-based magnetic liquid according to claim 1, characterized in that, The nanometer magnetic particle is at least one of Fe3O4, γ-Fe2O3 and CoFe2O4.

3. The perfluoropolyether-based magnetic liquid according to claim 1, wherein, The mass ratio of the pretreated perfluoropolyether surfactant to the nanometer magnetic particle is 1:3-1:5; and / or, the mass ratio of the nanometer magnetic particle to the perfluoropolyether-based carrier liquid is 1:2-1:

10.

4. The process for the preparation of a perfluoropolyether-based magnetic fluid according to any one of claims 1 to 3, characterized in that, The method comprises the following steps: S1. dissolving the perfluoropolyether surfactant in a transition liquid, then adding anhydride and catalyst to the transition liquid, evaporating the transition liquid after grafting reaction to obtain the pretreated perfluoropolyether surfactant; S2. dispersing the nanometer magnetic particle in ultrapure water, then adding the pretreated perfluoropolyether surfactant dropwise, then washing and drying the coated substance to obtain the coated nanometer magnetic particle; S3. dispersing the coated nanometer magnetic particle in the perfluoropolyether-based carrier liquid to obtain the perfluoropolyether-based magnetic liquid.

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

6. The preparation method according to claim 4, characterized in that, In step S1, the temperature of the grafting reaction is 80-120℃, and the time of the grafting reaction is 6-12h.

7. The preparation method according to claim 4, characterized in that, In step S1, the perfluoropolyether surfactant is dissolved in a transition liquid, then excess anhydride and catalyst are added to the transition liquid, after grafting reaction, ultrapure water is used to dissolve and clean the residual anhydride and catalyst for 3-5 times, then the transition liquid is evaporated to obtain the pretreated perfluoropolyether surfactant.

8. The preparation method according to claim 4, characterized in that, In step S2, the nanometer magnetic particle is dispersed in ultrapure water, the temperature of the water bath is adjusted to 70-100℃ and stirring is carried out, then the pretreated perfluoropolyether surfactant is added dropwise, stirring is carried out at a speed of 300-1000rpm for 15-30min, the coated substance is washed and dried to obtain the coated nanometer magnetic particle.

Images