Low-temperature-resistant magnetorheological fluid and preparation method thereof

Abstract

The invention relates to the technical field of intelligent materials, in particular to low-temperature-resistant magnetorheological fluid and a preparation method thereof.The low-temperature-resistant magnetorheological fluid is prepared from, by weight, 60-75 parts of magnetic particles; 3 to 15 parts of modified magnetic particles; 10-25 parts of low-temperature-based carrier liquid, which comprises 40-60% of silicone oil and / or mineral oil, 20-30% of synthetic ester and 10-20% of poly-alpha-olefin; 0.1 to 1.0 part of a dispersant; 0.5 to 2.0 parts of an anticoagulant; wherein the modified magnetic particles are prepared by coating magnetic particles with SiO2 aerogel and grafting the coated magnetic particles with fluorine-containing silane; the preparation method comprises the steps that magnetic particles are sequentially subjected to silane coupling agent treatment, aerogel deposition and fluorine-containing silane gas-phase grafting, and modified magnetic particles are prepared; carrying out ultrasonic mixing on the base carrier liquid and an anticoagulant at 40-60 DEG C for 30 minutes; adding magnetic particles, modified magnetic particles and a dispersing agent, dispersing by adopting a micro-jet homogenizer, and then carrying out gradient cooling treatment. The low-temperature-resistant magnetorheological fluid has the effect of improving the low-temperature-resistant performance of the magnetorheological fluid.

Description

Technical Field

[0001] The present application relates to the technical field of intelligent materials, and in particular, to a low-temperature resistant magnetorheological fluid and a preparation method thereof. Background Art

[0002] At present, magnetorheological fluid is an intelligent fluid composed of a base carrier fluid, magnetic particles and additives, and its rheological properties can be rapidly and reversibly regulated by an external magnetic field, and it is widely used in fields such as dampers and precision polishing.

[0003] Traditional magnetorheological fluids have the following problems in low-temperature environments: Conventional mineral oils or silicone oils have a sharp increase in viscosity or even solidify below -30°C, resulting in a sharp change in magnetorheological properties. In addition, the high-viscosity carrier fluid hinders the dynamic reorganization of particle chains, and the magnetic field switching response time is prolonged. These problems cause fluctuations in the output performance of damping devices and affect the control effect. Existing technologies partially improve the low-temperature performance by adding anticoagulants or adjusting the particle size. However, it is difficult to maintain stability below -40°C. Therefore, there is an urgent need for a magnetorheological fluid with both low-temperature fluidity, high magnetorheological effect and anti-settling properties. Summary of the Invention

[0004] In order to improve the low-temperature resistance performance of magnetorheological fluid, the present application provides a low-temperature resistant magnetorheological fluid and a preparation method thereof.

[0005] In a first aspect, a low-temperature resistant magnetorheological fluid provided by the present application adopts the following technical solution: A low-temperature resistant magnetorheological fluid is made of the following components by weight: 60-75 parts of magnetic particles; 3-15 parts of modified magnetic particles; 10-25 parts of a low-temperature base carrier fluid, including 40-60% of silicone oil and / or mineral oil, 20-30% of synthetic ester, 10-20% of polyalphaolefin; 0.1-1.0 part of a dispersant; 0.5-2.0 part of an anticoagulant; wherein the modified magnetic particles are obtained by coating magnetic particles with SiO 2 aerogel and grafting with fluorosilane.

[0006] By adopting the above technical solution, the low-viscosity characteristic of the composite base carrier fluid (-40°C kinematic viscosity ≤ 250 mPa·s) and the anticoagulant act synergistically to significantly inhibit the solidification of the carrier fluid; the core-shell structure of the modified magnetic particles (SiO 2 aerogel coating layer + fluorine-containing grafting layer) reduces particle agglomeration through physical adsorption and chemical hydrophobic action. Under a magnetic field, the shear yield stress is increased, so that the magnetic response performance is improved. The high magnetic permeability of the core-shell particles and the fluidity of the base carrier fluid ensure the rapid reorganization of the magnetic field-induced particle chains. The core-shell structure of the modified magnetic particles (SiO 2 aerogel buffers thermal stress, and the fluorine-containing grafting layer reduces ice crystal adsorption) and the low-viscosity composite carrier fluid act synergistically to significantly improve the low-temperature stability.

[0007] By defining the ratios of magnetic particles, modified magnetic particles, low-temperature base carrier fluids (silicone oil / synthetic ester / poly-α-olefin composite system), dispersants, and anticoagulants, the magnetorheological fluid has low viscosity (≤300 mPa·s), high anti-settling property (settling rate ≤10% in 72 hours), and strong magnetorheological effect (shear stress ≥75 kPa at 800 mT) at -40°C.

[0008] Optionally, the SiO 2 aerogel coating thickness of the modified magnetic particles is 50 - 100 nm.

[0009] By adopting the above technical solution, the SiO 2 aerogel coating layer has a thickness of 50 - 100 nm, maintaining the high porosity (≥90%) and structural stability of the coating layer. The high porosity (≥90%) of SiO 2 aerogel can absorb the thermal expansion difference between magnetic particles (such as carbonyl iron) and the base carrier fluid, avoid the rupture of the coating layer caused by interfacial stress at low temperature, inhibit low-temperature interfacial peeling, and avoid magnetic property loss caused by being too thick; a coating layer that is too thin (<50 nm) may not effectively isolate the direct contact between particles and the carrier fluid, resulting in interfacial oxidation; being too thick (>100 nm) will reduce the volume ratio of magnetic particles and weaken the magnetorheological effect.

[0010] Optionally, the dispersant is selected from polyether-modified siloxanes or hyperbranched polyester amides.

[0011] By adopting the above technical solution, the dispersant is polyether-modified siloxane or hyperbranched polyester amide. The branched-chain structure of polyether-modified siloxane adsorbs on the particle surface, forming a three-dimensional barrier to prevent particle aggregation due to van der Waals forces, creating a steric hindrance effect to prevent particle aggregation and maintain the uniformity of the magnetorheological fluid; the polar groups of hyperbranched polyester amide can increase the surface charge density of the particles and enhance electrostatic repulsion.

[0012] Optionally, the anticoagulant is selected from alkyl naphthalene derivatives or polymethacrylates.

[0013] By adopting the above technical solution, the anticoagulant alkyl naphthalene derivatives (such as dodecyl naphthalene) or polymethacrylates can effectively reduce the freezing point of the base fluid (≤ -60°C), inhibit low-temperature crystallization, and the synergistic effect of the anticoagulant and the composite carrier fluid ensures low-temperature fluidity; polymethacrylates reduce the intermolecular friction by adsorbing on the molecular chains of the carrier fluid.

[0014] Optionally, the particle size of the magnetic particles is 0.5 - 10 μm, and the magnetic particles are selected from at least one of carbonyl iron powder, cobalt powder, and nickel powder.

[0015] By adopting the above technical solution, the particle size of the magnetic particles is 0.5 - 10 μm, ensuring the balance between the magnetic response speed and the anti-settling property. Smaller particle sizes (such as 3 μm) have a higher specific surface area, accelerating the formation speed of particle chains under the magnetic field. Larger particle sizes (such as 5 μm) are more likely to settle due to gravity, but the low settling rate can still be maintained through the coating of modified particles and the action of the dispersant. If the particle size is too small, it is easy to settle (such as 0.4 μm), and if it is too large, the magnetorheological effect will be reduced (such as 11 μm).

[0016] Optionally, the contact angle of the fluorosilane grafting of the modified magnetic particles is ≥110°.

[0017] By adopting the above technical solution, the contact angle of the fluorosilane grafting of the modified magnetic particles is ≥110°. The low surface energy property of the fluorinated chain segment (such as perfluorodecyl) can reduce the nucleation of ice crystals on the particle surface, avoiding interface blockage at low temperatures. The hydrophobic layer reduces the frictional resistance between the particles and the carrier liquid, further improving the fluidity; and endows the particles with superhydrophobicity, reducing the adsorption of low-temperature ice crystals on the particle surface and avoiding the decrease in fluidity caused by interface blockage.

[0018] In a second aspect, a preparation method of a low-temperature resistant magnetorheological fluid provided by the present application adopts the following technical solution: A preparation method of a low-temperature resistant magnetorheological fluid includes the following steps: a. Immerse the magnetic particles in an ethanol solution of a silane coupling agent, perform ultrasonic treatment for 30 minutes, and dry at 80 °C; b. Add SiO 2 aerogel to the magnetic particles obtained in step a, stir at a constant temperature of 50 - 60 °C for 4 - 6 hours, and perform supercritical drying after aging for 24 hours to form a SiO 2 aerogel coating layer; c. In a vacuum reaction vessel, introduce fluorosilane into the magnetic particles with a SiO 2 aerogel coating layer obtained in step b, and perform gas-phase grafting at 120 - 150 °C for 2 - 4 hours to obtain modified magnetic particles; d. Take 10 - 25 parts by weight of a base carrier liquid and 0.5 - 2.0 parts of an anticoagulant, and ultrasonically mix them at 40 - 60 °C for 30 minutes to form a mixed liquid; e. Take 3 - 15 parts by weight of modified magnetic particles, 0.1 - 1.0 part of a dispersant, and 60 - 75 parts by weight of magnetic particles, mix them with the mixed liquid obtained in step d, and disperse them using a microfluidic homogenizer; f. Perform gradient cooling treatment on the liquid obtained in step e to obtain the magnetorheological fluid.

[0019] By adopting the above technical solutions, the surface activity of the reinforcing particles is enhanced through treatment with silane coupling agents, providing anchoring sites for aerogel deposition; the aerogel coating provides a thermal buffer layer, improving the thermal buffering effect; the grafting of fluorosilane enables the fluorine groups to be firmly grafted in the form of covalent bonds, enhancing the hydrophobicity, comprehensively improving the dispersibility and low-temperature stability of the particles, and the ultrasonic mixing of the base carrier liquid and the anticoagulant ensures uniform dispersion, reducing the low-temperature phase separation caused by uneven local concentration.

[0020] Optionally, in step f, a three-stage gradient cooling is adopted at 25 °C, -20 °C, and -40 °C, and each stage is kept warm for 2 hours.

[0021] By adopting the above technical solutions, the gradient cooling (25 °C → -20 °C → -40 °C) reduces the sudden change in thermal stress, allows the carrier liquid molecules to gradually adjust their conformations, reduces the damage to the microstructure caused by thermal stress, and stabilizes the microstructure of the magnetorheological fluid.

[0022] Optionally, in step e, 60 - 75 parts of magnetic particles are selected as the magnetic particles treated in step a.

[0023] By adopting the above technical solutions, the sedimentation resistance of the particles is improved by treating the magnetic particles with silane coupling agents.

[0024] Optionally, when using a microfluidic homogenizer for dispersion in step e, the shear rate ≥ 10^4 s -1 , the pressure is 1500 bar, and three cycles of dispersion are carried out.

[0025] By adopting the above technical solutions, the high shear force of the microfluidic homogenizer (≥ 10^4 s -1 , 1500 bar) evenly disperses the particles.

[0026] In summary, the present application has the following beneficial technical effects: Through the synergistic effect of core-shell structured magnetic particles (carbonyl iron / cobalt / nickel core + SiO 2 aerogel / fluoropolymer coating), a low-viscosity composite carrier liquid system (silicone oil and / or mineral oil, synthetic ester, polyalpha-olefin), and a multi-stage dispersion stabilizer, the intermediate layer of SiO 2 aerogel buffers the difference in thermal expansion coefficients, inhibits low-temperature interfacial peeling, and the fluorine-grafted layer reduces ice crystal adsorption, significantly reducing the low-temperature viscosity and improving the flow performance of the magnetorheological fluid. Detailed Embodiments

[0027] The following provides a further detailed description of the present application.

[0028] In the embodiments of the present application, a low-temperature resistant magnetorheological fluid and its preparation method are disclosed. In the embodiments, the experimental methods used are all conventional methods without special instructions, and the materials, reagents, etc. used can all be obtained from commercial channels without special instructions.

[0029] Example 1: A low-temperature resistant magnetorheological fluid of this example is made from the following components by weight: Among them, the magnetic particles are selected from 68 parts of carbonyl iron powder (D50 = 3 μm); modified magnetic particles: SiO 2 aerogel-coated + perfluorodecyltriethoxysilane-grafted carbonyl iron powder 12 parts; base carrier liquid 18 parts: including dimethyl silicone oil (50%) + pentaerythritol ester (30%) + PAO6 (20%); dispersant polyether-modified siloxane 0.5 part; anticoagulant dodecylnaphthalene 1.5 parts.

[0030] A preparation method of a low-temperature resistant magnetorheological fluid of this example includes the following steps: a. Immerse the magnetic particles in an ethanol solution of silane coupling agent (KH550), perform ultrasonic treatment for 30 minutes, and dry at 80°C; among them, the magnetic particles are selected as carbonyl iron powder; b. Add SiO 2 aerogel to the magnetic particles obtained in step a, stir at a constant temperature of 55°C for 5 hours, age for 24h, and then perform supercritical drying to form a SiO 2 aerogel coating layer; c. In a vacuum reaction vessel, introduce perfluorodecyltriethoxysilane into the magnetic particles with a SiO 2 aerogel coating layer obtained in step b, and perform gas-phase grafting at 150°C for 2 hours to obtain modified magnetic particles; Specifically, gradually add a SiO 2 precursor solution (TE0S as the precursor, catalyzed by ammonia water) to the magnetic particles treated in step a. The mass ratio of carbonyl iron powder to SiO 2 precursor is 1:10 - 1:5. In this example, the weight ratio of 1:7.5 is selected. This range can ensure the integrity and thickness controllability of the aerogel coating layer (controlled within 80nm ± 5nm). Stir at a constant temperature of 55°C for 5 hours to complete hydrolysis and condensation, age for 24h, and then perform supercritical drying to form a SiO 2 aerogel coating layer with a thickness of 80nm. By regulating the silane concentration (2 - 5vol%, preferably 3.5vol% in this example), grafting time of 3 hours, and temperature of 150°C, the surface energy is reduced to <20 mN / m, and the contact angle ≥ 110° is achieved.

[0031] d. Take 18 parts by weight of the base carrier liquid and 1.5 parts of the anticoagulant, and ultrasonically mix them at 50°C for 30 minutes to form a mixed solution; among them, the base carrier liquid includes dimethyl silicone oil (50%) + pentaerythritol ester (30%) + PAO6 (20%); the anticoagulant is selected as dodecylnaphthalene; e. Take 12 parts by weight of modified magnetic particles, 0.5 part of dispersant, and 68 parts of magnetic particles, mix them with the mixed solution obtained in step d, and disperse them using a microfluidic homogenizer, where the shear rate ≥ 10^4 s -1 , the pressure is 1500 bar, and perform 3 cycles of dispersion; the dispersant is selected as polyether-modified silicone; the magnetic particles are selected as the magnetic particles obtained in step a; f. Gradually cool the liquid obtained in step e at three stages of 25°C, -20°C, and -40°C, and keep warm for 2 hours at each stage to obtain the magnetorheological fluid.

[0032] Example 2: A low-temperature resistant magnetorheological fluid of this example is made of the following components by weight: the magnetic particles are selected from 68 parts of cobalt powder (D50 = 3 μm); modified magnetic particles: SiO 2 Cobalt powder coated with aerogel + grafted with perfluorodecyltriethoxysilane, 12 parts; base carrier liquid 18 parts: including phenyl silicone oil (55%) + trimethylolpropane ester (25%) + PAO4 (20%); dispersant hyperbranched polyester amide 0.8 part; anticoagulant polymethacrylate 1.2 parts.

[0033] A preparation method of a low-temperature resistant magnetorheological fluid of this example includes the following steps: a. Immerse the magnetic particles in an ethanol solution of silane coupling agent (KH550), perform ultrasonic treatment for 30 minutes, and dry at 80°C; the magnetic particles are selected as cobalt powder; b. Add SiO 2 aerogel to the magnetic particles obtained in step a, stir at a constant temperature of 55°C for 5 hours, age for 24h, and then perform supercritical drying to form a SiO 2 aerogel coating layer; c. In a vacuum reaction vessel, introduce perfluorodecyltriethoxysilane into the magnetic particles with a SiO 2 aerogel coating layer obtained in step b, and perform gas-phase grafting at 150°C for 2 hours to obtain modified magnetic particles; Specifically, gradually add a SiO 2 precursor solution (TE0S as the precursor, catalyzed by ammonia water) dropwise to the magnetic particles treated in step a. The mass ratio of cobalt powder to SiO 2 precursor is 1:10 to 1:5. In this example, the weight ratio of 1:7.5 is selected. This range can ensure the integrity and thickness controllability of the aerogel coating layer (controlled within 80nm ± 5nm). Stir at a constant temperature of 55°C for 5 hours to complete hydrolysis and condensation, age for 24h, and then perform supercritical drying to form SiO 2Aerogel coating layer with a thickness of 80 nm. By controlling the silane concentration (2 - 5 vol%, preferably 3.5 vol% in this example), grafting time of 3 hours, and temperature of 150 °C, the surface energy is reduced to <20 mN / m, achieving a contact angle ≥110°.

[0034] d. Take 18 parts by weight of the base carrier liquid and 1.2 parts of the anticoagulant, and ultrasonically mix them at 50 °C for 30 minutes to form a mixed liquid; the base carrier liquid contains phenyl silicone oil (55%) + trimethylolpropane ester (25%) + PAO4 (20%); the anticoagulant is selected as methacrylate; e. Take 12 parts by weight of the modified magnetic particles, 0.8 parts of the dispersant, and 68 parts of the magnetic particles, mix them with the mixed liquid prepared in step d, and disperse them using a microfluidic homogenizer, where the shear rate ≥10^4 s -1 , pressure 1500 bar, and perform 3 cycles of dispersion; the dispersant is selected as hyperbranched polyester amide; the magnetic particles are the magnetic particles prepared in step a; f. Gradually cool the liquid prepared in step e in three stages of 25 °C, -20 °C, and -40 °C, and keep it warm for 2 hours at each stage to obtain the magnetorheological fluid.

[0035] Example 3: A low-temperature resistant magnetorheological fluid in this example is made of the following components by weight: among them, the magnetic particles are selected from 68 parts of iron-nickel alloy powder (D50 = 3 μm); modified magnetic particles: SiO 2 Iron-nickel alloy powder grafted with aerogel coating + perfluorodecyltriethoxysilane 12 parts; 18 parts of the base carrier liquid: containing mineral oil (55%) + trimethylolpropane ester (25%) + PAO4 (20%); 0.8 parts of the dispersant polyether-modified silicone; 1.2 parts of the anticoagulant dodecylnaphthalene.

[0036] The preparation method of a low-temperature resistant magnetorheological fluid in this example includes the following steps: a. Immerse the magnetic particles in an ethanol solution of silane coupling agent (KH550), ultrasonically treat for 30 minutes, and dry at 80 °C; the magnetic particles are selected as iron-nickel alloy powder; b. Add SiO 2 aerogel to the magnetic particles prepared in step a, stir at a constant temperature of 55 °C for 5 hours, age for 24 h, and then perform supercritical drying to form a SiO 2 aerogel coating layer; c. In a vacuum reaction vessel, pass perfluorodecyltriethoxysilane into the magnetic particles with the SiO 2 aerogel coating layer prepared in step b, and perform gas-phase grafting at 150 °C for 2 hours to obtain the modified magnetic particles; Specifically, gradually add SiO dropwise to the magnetic particles treated in step a2 Precursor solution (TEOS as the precursor, catalyzed by ammonia water), the mass ratio of iron-nickel alloy powder to SiO 2 The mass ratio of the precursor is 1:10 to 1:5. In this example, a weight ratio of 1:7.5 is selected. This range can ensure the integrity and thickness controllability of the aerogel coating layer (controlled within 80nm ± 5nm). Stir at a constant temperature of 55°C for 5 hours to complete hydrolysis and condensation, and perform supercritical drying after aging for 24h to form SiO 2 Aerogel coating layer with a thickness of 80nm. By regulating the silane concentration (2 - 5vol%, preferably 3.5vol% in this example), grafting time of 3 hours, and temperature of 150°C, the surface energy is reduced to <20 mN / m, achieving a contact angle ≥ 110°.

[0037] d. Take 18 parts by weight of the base carrier liquid and 1.2 parts of the anticoagulant, and ultrasonically mix them at 50°C for 30 minutes to form a mixed liquid; the base carrier liquid contains mineral oil (55%) + trimethylolpropane ester (25%) + PAO4 (20%); the anticoagulant is selected as dodecylnaphthalene; e. Take 12 parts by weight of the modified magnetic particles, 0.8 parts of the dispersant, and 68 parts of the magnetic particles, and mix them with the mixed liquid prepared in step d, and disperse them using a microfluidic homogenizer, where the shear rate ≥ 10^4 s -1 , pressure 1500 bar, and perform 3 cycles of dispersion; the dispersant is selected as polyether-modified siloxane; the magnetic particles are the magnetic particles prepared in step a; f. Gradually cool the liquid prepared in step e in three stages at 25°C, -20°C, and -40°C, and keep it warm for 2 hours at each stage to obtain the magnetorheological fluid.

[0038] Example 4: A low-temperature resistant magnetorheological fluid in this example is made of the following components by weight: the magnetic particles are selected from 75 parts of carbonyl iron powder (D50 = 3 μm); modified magnetic particles: SiO 2 Carbonyl iron powder grafted with aerogel coating + perfluorodecyltriethoxysilane, 5 parts; 18 parts of the base carrier liquid: containing mineral oil (55%) + trimethylolpropane ester (25%) + PAO4 (20%); 0.8 parts of the dispersant polyether-modified siloxane; 1.2 parts of the anticoagulant dodecylnaphthalene.

[0039] The preparation method of a low-temperature resistant magnetorheological fluid in this example includes the following steps: a. Immerse the magnetic particles in an ethanol solution of silane coupling agent (KH550), ultrasonically treat for 30 minutes, and dry at 80°C; the magnetic particles are selected as carbonyl iron powder; b. Add SiO to the magnetic particles prepared in step a 2Aerogel, stirred at a constant temperature of 55 °C for 5 hours, supercritically dried after aging for 24 h to form SiO 2 aerogel coating; c. In a vacuum reaction vessel, perfluorodecyltriethoxysilane was introduced into the magnetic particles with an aerogel coating of SiO 2 prepared in step b, and gas-phase grafting was carried out at 150 °C for 2 hours to obtain modified magnetic particles; Specifically, SiO was added dropwise to the magnetic particles treated in step a 2 precursor solution (TE0S as the precursor, catalyzed by ammonia water), and the mass ratio of carbonyl iron powder to SiO 2 precursor was 1:10 - 1:5. In this example, the weight ratio was selected as 1:7.5. This range can ensure the integrity and thickness controllability of the aerogel coating (controlled within 80 nm ± 5 nm). Stir at a constant temperature of 55 °C for 5 hours to complete hydrolysis and condensation. After aging for 24 h, supercritical drying was carried out to form SiO 2 aerogel coating with a thickness of 80 nm. By regulating the silane concentration (2 - 5 vol%, preferably 3.5 vol% in this example), grafting time of 3 hours, and temperature of 150 °C, the surface energy was reduced to <20 mN / m, achieving a contact angle ≥110°.

[0040] d. Take 18 parts by weight of the base carrier liquid and 1.2 parts of the anticoagulant, and ultrasonically mix them at 50 °C for 30 minutes to form a mixed liquid; the base carrier liquid contains mineral oil (55%) + trimethylolpropane ester (25%) + PAO4 (20%); the anticoagulant is selected as dodecylnaphthalene; e. Take 5 parts by weight of the modified magnetic particles, 0.8 parts of the dispersant, and 75 parts of the magnetic particles, and mix them with the mixed liquid prepared in step d. Use a microfluidic homogenizer for dispersion, where the shear rate ≥10^4 s -1 , pressure 1500 bar, and perform 3 cycles of dispersion; the dispersant is selected as polyether-modified silicone; the magnetic particles are the magnetic particles prepared in step a; f. Gradually cool the liquid prepared in step e in three stages of 25 °C, -20 °C, and -40 °C, and keep it warm for 2 hours at each stage to obtain the magnetorheological fluid.

[0041] Comparative Example 1: This Comparative Example 1 verifies the improvement effect of SiO 2 aerogel coating + fluorosilane grafting on particle dispersibility, antioxidant property, and interfacial stability. It is made of the following components by weight: among them, the magnetic particles are selected from 80 parts of carbonyl iron powder (D50 = 3 μm); modified magnetic particles: none; 18 parts of the base carrier liquid: containing 50% dimethyl silicone oil + 30% pentaerythritol ester + 20% PAO6; 0.5 part of the dispersant polyether-modified silicone; 1.5 parts of the anticoagulant dodecylnaphthalene.

[0042] The preparation method of the magnetorheological fluid of this comparative example includes the following steps: a. Immerse the magnetic particles in an ethanol solution of silane coupling agent (KH550), ultrasonically treat for 30 minutes, and dry at 80 °C; among them, the magnetic particles are carbonyl iron powder. b. Take 18 parts by weight of the base carrier liquid and 1.5 parts of the anticoagulant, ultrasonically mix at 50 °C for 30 minutes to form a mixed liquid; among them, the base carrier liquid contains mineral oil (55%) + trimethylolpropane ester (25%) + PAO4 (20%); the anticoagulant is dodecylnaphthalene. c. Take 0.5 part by weight of the dispersant and 80 parts of the magnetic particles, mix them with the mixed liquid prepared in step b, and disperse them using a microfluidic homogenizer, where the shear rate ≥ 10^4 s -1 , the pressure is 1500 bar, and perform 3 cycles of dispersion; among them, the dispersant is polyether-modified silicone. d. Gradually cool the liquid prepared in step c at three stages of 25 °C, -20 °C, and -40 °C, and keep warm for 2 hours at each stage to obtain the magnetorheological fluid.

[0043] Comparative Example 2: This Comparative Example 2 verifies the synergistic advantages of the composite base carrier liquid (silicone oil + esters + PAO) compared with single silicone oil in viscosity regulation, temperature adaptability, and lubricity. It is made of the following components by weight: Among them, the magnetic particles are selected from 68 parts of carbonyl iron powder (D50 = 3 μm); modified magnetic particles: SiO 2 Carbonyl iron powder grafted with aerogel coating + perfluorodecyltriethoxysilane 12 parts; 18 parts of the base carrier liquid: containing 100% dimethyl silicone oil; 0.5 part of the dispersant polyether-modified silicone; 1.5 parts of the anticoagulant dodecylnaphthalene.

[0044] The preparation method of the magnetorheological fluid of this comparative example includes the following steps: a. Immerse the magnetic particles in an ethanol solution of silane coupling agent (KH550), ultrasonically treat for 30 minutes, and dry at 80 °C; among them, the magnetic particles are carbonyl iron powder. b. Add SiO 2 aerogel to the magnetic particles obtained in step a, stir at a constant temperature of 55 °C for 5 hours, and perform supercritical drying after aging for 24 hours to form a SiO 2 aerogel coating layer. c. In a vacuum reaction vessel, pass perfluorodecyltriethoxysilane through the magnetic particles with the SiO 2 aerogel coating layer obtained in step b, and perform gas-phase grafting at 150 °C for 2 hours to obtain modified magnetic particles; among them, the magnetic particles are the magnetic particles obtained in step a. Specifically, gradually add SiO dropwise to the magnetic particles treated in step a.2 Precursor solution (TEOS as the precursor, catalyzed by ammonia water), the mass ratio of carbonyl iron powder to SiO 2 is 1:10 to 1:5. In this example, the weight ratio is selected as 1:7.5. This range can ensure the integrity and thickness controllability of the aerogel coating layer (controlled within 80nm ± 5nm). Stir at a constant temperature of 55°C for 5 hours to complete hydrolysis and condensation. After aging for 24 hours, perform supercritical drying to form SiO 2 aerogel coating layer with a thickness of 80nm. By regulating the silane concentration (2 - 5 vol%, preferably 3.5 vol% in this example), grafting time of 3 hours, and temperature of 150°C, the surface energy is reduced to <20 mN / m, achieving a contact angle ≥ 110°.

[0045] d. Take 18 parts by weight of the base carrier liquid and 1.5 parts of the anticoagulant, and ultrasonically mix them at 50°C for 30 minutes to form a mixed liquid; the base carrier liquid contains 100% dimethyl silicone oil; the anticoagulant is selected as dodecylnaphthalene; e. Take 12 parts by weight of the modified magnetic particles, 0.5 parts of the dispersant, and 68 parts of the magnetic particles, and mix them with the mixed liquid prepared in step d. Use a microfluidic homogenizer for dispersion, where the shear rate ≥ 10^4 s -1 , the pressure is 1500 bar, and perform 3 cycles of dispersion; the dispersant is selected as polyether-modified silicone; the magnetic particles are selected as the magnetic particles prepared in step a; f. Gradually cool the liquid prepared in step e in three stages at 25°C, -20°C, and -40°C, and keep it warm for 2 hours at each stage to obtain the magnetorheological fluid.

[0046] Perform actual sedimentation tests on the magnetorheological fluids prepared in Examples 1 to 4, Comparative Example 1, and Comparative Example 2. The test method is as follows: (1) Test the relationship between viscosity and shear rate on a rheometer, and take the point of the final shear rate as the zero-field viscosity of the magnetorheological fluid; (2) Test the relationship between shear stress and shear rate on a rheometer, perform polar linear fitting, and take the intercept of the fitting as the shear yield stress of the magnetorheological fluid; (3) Prepare a 50 mL sample, pour it into a graduated cylinder, fix the observation at 5 pm every day, measure the height of the supernatant liquid above, and the anti-sedimentation rate = (height of the upper supernatant liquid / total height) * 100%; the test results are shown in Table 1 below.

[0047] Table 1 Example Performance Example 1 Example 2 Example 3 Example 4 Comparative Example 1 Comparative Example 2 Zero-field Viscosity at 25°C 0.25712 0.24177 0.19712 0.18189 0.79256 0.11268 Zero-field Viscosity at -40°C 0.27391 0.25657 0.22898 0.20212 0.98742 0.58395 Shear Yield Stress at 25°C and 100 mT (kPa) 2.57724 2.60286 2.59268 2.53233 1.71722 2.01673 Shear Yield Stress at 25°C and 800 mT (kPa) 79.12398 79.02536 80.81655 78.85026 58.34175 63.45391 Shear Yield Stress at -40°C and 100 mT (kPa) 2.34917 2.36321 2.59303 2.57233 1.02116 1.59528 Shear Yield Stress at -40°C and 800 mT (kPa) 82.91177 77.08703 77.81491 76.85026 46.86773 55.5478 Sedimentation Resistance at 25°C for 30 Days (%) 13.72 14.33 11.6 12.24 33.52 30.56 Sedimentation Resistance at -40°C for 30 Days (%) 13.19 13.84 10.07 11.69 30.81 28.93 As can be seen from the table, the magnetorheological fluid prepared by the present invention has good low-temperature resistance, has a low zero-field viscosity and good anti-sedimentation property at -40°C, as well as a high magneto-induced shear yield stress.

[0048] Example 5: A low-temperature resistant magnetorheological fluid of this example is made from the following components by weight: Among them, the magnetic particles are selected from 70 parts of carbonyl iron powder (D50 = 5 μm); modified magnetic particles: SiO 2 aerogel-coated and perfluorodecyltriethoxysilane-grafted carbonyl iron powder 8 parts; base carrier liquid 20 parts: including phenyl silicone oil (60%) + trimethylolpropane ester (20%) + PAO6 (20%); dispersant hyperbranched polyester amide 0.6 part; anticoagulant polymethacrylate 1.4 parts.

[0049] A preparation method of a low-temperature resistant magnetorheological fluid of this example includes the following steps: a. Immerse the magnetic particles in an ethanol solution of silane coupling agent (KH550), perform ultrasonic treatment for 30 minutes, and dry at 80 °C; among them, the magnetic particles are selected as carbonyl iron powder; b. Add SiO 2 aerogel to the magnetic particles obtained in step a, stir at a constant temperature of 55 °C for 5 hours, and perform supercritical drying after aging for 24 hours to form a SiO 2 aerogel coating layer; c. In a vacuum reaction vessel, introduce perfluorodecyltriethoxysilane into the magnetic particles with a SiO 2 aerogel coating layer obtained in step b, and perform gas-phase grafting at 150 °C for 2 hours to obtain modified magnetic particles; Specifically, gradually add a SiO 2 precursor solution (TEOS as the precursor, catalyzed by ammonia water) to the magnetic particles treated in step a. The mass ratio of carbonyl iron powder to SiO 2 precursor is 1:10 to 1:5. In this example, the weight ratio of 1:7.5 is selected. This range can ensure the integrity and thickness controllability of the aerogel coating layer (controlled within 80 nm ± 5 nm). Stir at a constant temperature of 55 °C for 5 hours to complete hydrolysis and condensation, and perform supercritical drying after aging for 24 hours to form a SiO 2 aerogel coating layer with a thickness of 80 nm. By regulating the silane concentration (2 - 5 vol%, preferably 3.5 vol% in this example), grafting time of 3 hours, and temperature of 150 °C, the surface energy is reduced to <20 mN / m, and the contact angle ≥ 110° is achieved.

[0050] d. Take 20 parts by weight of the base carrier liquid and 1.4 parts of the anticoagulant, and ultrasonically mix them at 50 °C for 30 minutes to form a mixed solution; among them, the base carrier liquid contains mineral oil (55%) + trimethylolpropane ester (25%) + PAO4 (20%); the anticoagulant is selected as polymethacrylate; e. Take 8 parts by weight of modified magnetic particles, 0.6 parts of dispersant, and 70 parts of magnetic particles, mix them with the mixed solution obtained in step d, and disperse them using a microfluidic homogenizer, where the shear rate ≥ 10^4 s -1 , the pressure is 1500 bar, and perform 3 cycles of dispersion; the dispersant is selected as hyperbranched polyester amide; the magnetic particles are selected as the magnetic particles prepared in step a; f. Gradually cool the liquid obtained in step e in three stages at 25°C, -20°C, and -40°C, and keep it warm for 2 hours at each stage to obtain the magnetorheological fluid.

[0051] Example 6: A low-temperature resistant magnetorheological fluid in this example is made of the following components by weight: The magnetic particles are selected from 68 parts of cobalt powder (D50 = 5μm); Modified magnetic particles: SiO 2 aerogel-coated + perfluorodecyltriethoxysilane-grafted cobalt powder 12 parts; Base carrier liquid 18 parts: including phenyl silicone oil (45%) + pentaerythritol ester (35%) + PAO4 (20%); Dispersant polyether-modified silicone 0.6 parts; Anticoagulant dodecylnaphthalene 1.2 parts.

[0052] A preparation method of a low-temperature resistant magnetorheological fluid in this example includes the following steps: a. Immerse the magnetic particles in an ethanol solution of silane coupling agent (KH550), ultrasonically treat for 30 minutes, and dry at 80°C; the magnetic particles are selected as cobalt powder; b. Add SiO 2 aerogel to the magnetic particles obtained in step a, stir at a constant temperature of 55°C for 5 hours, age for 24h, and then supercritically dry to form a SiO 2 aerogel coating layer; c. In a vacuum reaction vessel, introduce perfluorodecyltriethoxysilane into the magnetic particles with a SiO 2 aerogel coating layer obtained in step b, and perform gas-phase grafting at 150°C for 2 hours to obtain modified magnetic particles; Specifically, gradually add a SiO 2 precursor solution (TE0S as the precursor, catalyzed by ammonia water) dropwise to the magnetic particles treated in step a. The mass ratio of cobalt powder to SiO 2 precursor is 1:10 - 1:5. In this example, the weight ratio is selected as 1:8.5. Stir at a constant temperature of 55°C for 5 hours to complete hydrolysis and condensation, age for 24h, and then supercritically dry to form a SiO 2 aerogel coating layer with a thickness of 90nm. By regulating the silane concentration (2 - 5 vol%, preferably 3.5 vol% in this example), grafting time of 3 hours, and temperature of 150°C, the surface energy is reduced to <20 mN / m, and the contact angle ≥ 110° is achieved.

[0053] d. Take 18 parts by weight of the base carrier liquid and 1.2 parts of the anticoagulant, and ultrasonically mix them at 50 °C for 30 minutes to form a mixed liquid; the base carrier liquid contains phenyl silicone oil (45%) + pentaerythritol ester (35%) + PAO4 (20%); the anticoagulant is selected as dodecylnaphthalene; e. Take 12 parts by weight of the modified magnetic particles, 0.8 parts of the dispersant, and 68 parts of the magnetic particles, mix them with the mixed liquid prepared in step d, and disperse them using a microfluidic homogenizer, where the shear rate ≥ 10^4 s -1 , the pressure is 1500 bar, and perform 3 cycles of dispersion; the dispersant is selected as polyether-modified silicone; the magnetic particles are the magnetic particles prepared in step a; f. Gradually cool the liquid prepared in step e at three stages of 25 °C, -20 °C, and -40 °C, and keep it warm for 2 hours at each stage to obtain the magnetorheological fluid.

[0054] Example 7: A low-temperature-resistant magnetorheological fluid in this example is made of the following components by weight: the magnetic particles are selected from 68 parts of iron-nickel alloy powder (D50 = 5 μm); modified magnetic particles: SiO 2 aerogel-coated and perfluorodecyltriethoxysilane-grafted iron-nickel alloy powder 11.5 parts; base carrier liquid 18 parts: containing mineral oil (55%) + trimethylolpropane ester (25%) + PAO4 (20%); dispersant polyether-modified silicone 0.7 parts; anticoagulant dodecylnaphthalene 1.8 parts.

[0055] A preparation method of a low-temperature-resistant magnetorheological fluid in this example includes the following steps: a. Immerse the magnetic particles in an ethanol solution of silane coupling agent (KH550), ultrasonically treat for 30 minutes, and dry at 80 °C; the magnetic particles are selected as iron-nickel alloy powder; b. Add SiO 2 aerogel to the magnetic particles prepared in step a, stir at a constant temperature of 55 °C for 5 hours, age for 24 h, and then perform supercritical drying to form a SiO 2 aerogel coating layer; c. In a vacuum reaction vessel, pass perfluorodecyltriethoxysilane into the magnetic particles with the SiO 2 aerogel coating layer prepared in step b, and perform gas-phase grafting at 150 °C for 2 hours to obtain the modified magnetic particles; Specifically, gradually add a SiO 2 precursor solution (TE0S as the precursor, catalyzed by ammonia water) dropwise to the magnetic particles treated in step a, and the iron-nickel alloy powder and SiO 2The mass ratio of the precursors is 1:10 to 1:5. In this example, a weight ratio of 1:7.5 is selected, and stirring is carried out at a constant temperature of 55 °C for 5 hours to complete hydrolysis and condensation. After aging for 24 h, supercritical drying is carried out to form SiO 2 aerogel coating layer with a thickness of 80 nm. By regulating the silane concentration (2 - 5 vol%, preferably 3.5 vol% in this example), grafting time of 3 hours, and temperature of 150 °C, the surface energy is reduced to <20 mN / m, achieving a contact angle ≥110°.

[0056] d. Take 18 parts by weight of the base carrier liquid and 1.8 parts of the anticoagulant, and ultrasonically mix them at 50 °C for 30 minutes to form a mixed liquid; the base carrier liquid contains phenyl silicone oil (45%) + pentaerythritol ester (35%) + PAO4 (20%); the anticoagulant is selected as dodecylnaphthalene; e. Take 11.5 parts by weight of the modified magnetic particles, 0.7 part of the dispersant, and 68 parts of the magnetic particles, mix them with the mixed liquid prepared in step d, and disperse them using a microfluidic homogenizer, where the shear rate ≥10^4 s -1 , pressure 1500 bar, and perform 3 cycles of dispersion; the dispersant is selected as polyether-modified silicone; the magnetic particles are selected as the magnetic particles prepared in step a; f. Gradually cool the liquid prepared in step e in three stages of 25 °C, -20 °C, and -40 °C, and keep it warm for 2 hours at each stage to obtain the magnetorheological fluid.

[0057] Example 8: The difference from Example 5 is that the modified magnetic particles are changed to 15 parts, the magnetic particles are changed to 65 parts, and the composition of the base carrier liquid is changed to mineral oil (50%) + trimethylolpropane ester (25%) + PAO6 (25%); the preparation method steps remain unchanged; Comparative Example 3: The difference from Example 5 is that the base carrier liquid is changed to 21.4 parts and no anticoagulant is used; the preparation method steps remain unchanged.

[0058] Comparative Example 4: The difference from Example 5 is that the base carrier liquid is a single lipid, 100% pentaerythritol ester, and the preparation method and steps remain unchanged.

[0059] Perform actual sedimentation tests on the magnetorheological fluids prepared in Examples 5 to 8, Comparative Example 3, and Comparative Example 4, and the test results are shown in Table 2 below.

[0060] Table 2 Example Performance Example 5 Example 6 Example 7 Example 8 Comparative Example 3 Comparative Example 4 Zero-field Viscosity at 25°C 0.23812 0.24217 0.20812 0.19523 0.31522 0.41821 Zero-field Viscosity at -40°C 0.25521 0.25834 0.22512 0.21022 1.20312 0.89231 Shear Yield Stress at 25°C and 100 mT (kPa) 2.36324 2.85236 2.62268 2.78453 1.52231 1.85673 Shear Yield Stress at 25°C and 800 mT (kPa) 78.31328 76.51436 80.31215 83.22621 52.34175 65.23391 Shear Yield Stress at -40°C and 100 mT (kPa) 2.12317 2.43321 2.38303 2.52233 0.78612 1.12342 Shear Yield Stress at -40°C and 800 mT (kPa) 75.91217 73.93703 78.12491 79.85026 32.67534 48.56278 Sedimentation Resistance at 25°C for 30 Days (%) 13.52 14.21 12.12 10.80 38.72 28.56 Sedimentation Resistance at -40°C for 30 Days (%) 13.01 13.82 11.72 10.32 41.2 26.93 Comparing Comparative Example 3 with Examples 5 - 8, the absence of the anticoagulant significantly increased the zero - field viscosity at - 40°C, indicating that the anticoagulant significantly reduced the low - temperature viscosity by inhibiting the crystallization of the base carrier liquid. The shear stress of Comparative Example 3 at 800 mT was only 52.34 kPa (25°C) and 32.67 kPa (-40°C), much lower than 75 - 83 kPa of Examples 5 - 8. The anticoagulant improved the fluidity and promoted the rapid reorganization of particle chains under the magnetic field. The sedimentation rate of Comparative Example 3 was as high as 38.7% (25°C) and 41.2% (-40°C), while that of Examples 5 - 8 was ≤15%. The anticoagulant reduced the viscosity fluctuation of the carrier liquid and inhibited particle agglomeration.

[0061] Comparing Comparative Example 4 with Examples 5 - 8, it can be seen that the composite base carrier liquid has a synergistic effect, which helps to optimize the fluidity. The shear stress of Comparative Example 4 at 800 mT was 65.23 kPa (25°C) and 48.56 kPa (-40°C), while that of Examples 5 - 8 was ≥75 kPa. The composite carrier liquid ensured the dynamic reorganization efficiency of particle chains. The sedimentation rate of Comparative Example 4 (28.5%) was significantly higher than that of Examples 5 - 8 (≤15%). The composite carrier liquid reduced particle sedimentation through viscosity balance.

[0062] Comparing Example 5 with Example 1, the variable difference is that the particle size of carbonyl iron powder becomes larger, and the weight parts of the base carrier liquid and magnetic particles increase. The viscosity of the product in Example 5 at 25°C slightly rises to 0.238 Pa·s (original 0.257), and the fluidity of large - particle size decreases slightly; the shear stress remains 78.3 kPa (800 mT), and the increase in particle size has little effect on magnetic properties.

[0063] Comparing Example 6 with Example 1, the magnetic particles are replaced with cobalt powder, and the proportion of lipids in the base carrier liquid increases. The magnetic permeability of cobalt powder is slightly lower, and the shear stress at 800 mT drops to 76.5 kPa (compared with 79.1 kPa of Example 1); the polarity of esters is enhanced, and the viscosity at - 40°C is 0.258 Pa·s, which is better than that of Example 1 (0.273 Pa·s).

[0064] Comparing Example 7 with Example 1, the magnetic particles are iron - nickel alloy powder, and the base carrier liquid is replaced with a mineral oil system. The iron - nickel alloy has excellent magnetic properties, and the shear stress at 800 mT reaches 80.3 kPa (better than Example 1); the viscosity of the mineral oil is slightly higher, and the sedimentation rate is 12.1% (compared with 13.7% of Example 1).

[0065] Comparing Example 8 with Example 1, the proportion of modified magnetic particles increases, and the base carrier liquid decreases. The modified particles improve the interfacial stability, and the shear stress at 800 mT reaches 83.2 kPa (the highest value); the reduction of the base carrier liquid results in the sedimentation rate dropping to 10.8% (the optimal value).

[0066] According to the comparison between the above-mentioned examples and comparative examples, the anticoagulant and base carrier liquid composite system is the core of low-temperature performance: the absence of anticoagulant (Comparative Example 3) or a single base carrier liquid (Comparative Example 4) leads to a sharp increase in viscosity and a weakening of magnetic response, and the composite base carrier liquid + anticoagulant synergistically optimizes low-temperature fluidity and stability.

[0067] The type and particle size of magnetic particles affect magnetic response and fluidity: the magnetic permeability of cobalt powder is slightly lower, and iron-nickel alloy performs better; the influence of large-particle-size particles (5 μm) on fluidity is controllable.

[0068] The proportion of modified particles and the coating process are the key: increasing the proportion of modified particles (Example 8) can improve interface stability, reduce sedimentation and enhance magnetic response.

[0069] Verification of the universality of Examples 1-8: All examples meet the requirements of viscosity ≤ 0.3 Pa·s, shear stress ≥ 75 kPa, and sedimentation rate ≤ 15% at -40°C, proving the reliability and scalability of the formulation design in extreme low-temperature scenarios.

[0070] Example 9: The difference from Example 5 lies in that the particle size of magnetic particles: D50 = 2 μm; the dispersant is 0.9 parts of hyperbranched polyester amide; the anticoagulant: 1.1 parts of dodecylnaphthalene; the magnetic particles: 70 parts of carbonyl iron powder; the modified magnetic particles: 10 parts; the preparation method and steps remain unchanged.

[0071] Example 10: The difference from Example 5 lies in that the anticoagulant: 1.5 parts of polymethacrylate; the dispersant: 0.5 parts of hyperbranched polyester amide; the base carrier liquid: phenyl silicone oil (50%) + trimethylolpropane ester (30%) + PAO6 (20%) → 18 parts; the modified magnetic particles: 12 parts.

[0072] For the preparation method, modify the aerogel coating time to 6 hours and the coating thickness to 100 nm.

[0073] Example 11: The difference from Example 5 lies in that the magnetic particles: 70 parts of nickel powder, and the base carrier liquid 20 parts: mineral oil (50%) + pentaerythritol ester (30%) + PAO6 (20%); The preparation method steps remain unchanged.

[0074] Example 12: The difference from Example 5 lies in that the magnetic particles: 68 parts; the modified magnetic particles: 12 parts; the base carrier liquid 18 parts: dimethyl silicone oil (35%) + trimethylolpropane ester (40%) + PAO4 (25%); The preparation method steps remain unchanged.

[0075] Comparative Example 5: The difference from Example 1 is that no dispersant is used, and the remaining weight fractions are adjusted: magnetic particles: 68 parts; modified magnetic particles: 12 parts; base carrier liquid: 18.5 parts; anticoagulant: 1.5 parts; The steps of the preparation method remain unchanged.

[0076] Comparative Example 6: The difference from Example 1 is that no original magnetic particles are used, and modified magnetic particles: 80 parts; the steps of the preparation method remain unchanged.

[0077] Perform actual sedimentation tests on the magnetorheological fluids prepared in Examples 9 to 12, Comparative Example 5, and Comparative Example 6. The test results are shown in Table 3 below.

[0078] Table 3 Example Performance Example 9 Example 10 Example 11 Example 12 Comparative Example 5 Comparative Example 6 Zero-field Viscosity at 25°C 0.252243 0.21843 0.24522 0.26313 0.68522 0.33221 Zero-field Viscosity at -40°C 0.27312 0.23624 0.26213 0.27821 1.50212 0.41511 Shear Yield Stress at 25°C and 100 mT (kPa) 2.95324 2.68236 2.78228 2.88153 1.45231 1.92173 Shear Yield Stress at 25°C and 800 mT (kPa) 76.81218 79.61436 77.53153 76.12621 46.32125 62.15121 Shear Yield Stress at -40°C and 100 mT (kPa) 2.61217 2.41211 2.50023 2.56133 0.82112 1.38342 Shear Yield Stress at -40°C and 800 mT (kPa) 74.52127 77.23503 75.22191 73.55026 28.75341 49.67278 Sedimentation Resistance at 25°C for 30 Days (%) 14.51 12.32 13.21 15.21 44.62 22.71 Sedimentation Resistance at -40°C for 30 Days (%) 14.01 11.92 12.82 14.62 42.82 20.53 Compared with Examples 1-12, in Comparative Example 5, due to the absence of the dispersant, the particles agglomerate severely due to van der Waals forces, resulting in a sharp increase in viscosity; the shear stress at 800 mT is only 46.32 kPa, and the particle chains are difficult to effectively reorganize; the sedimentation rate after 30 days exceeds 44%, much higher than 13.7% of Example 1.

[0079] Compared with Examples 1-12, in Comparative Example 6, the proportion of SiO 2 aerogel in the modified particles is high (80 parts), diluting the volume of the magnetic phase, resulting in the shear stress at 800 mT dropping to 62.15 kPa; the SiO 2 layer between particles thickens, increasing the interfacial friction, and the viscosity at -40 °C rises; the sedimentation rate after 30 days is 22.7%, and the difference in density of the modified particles leads to a decrease in dispersion stability.

[0080] Compared with Example 1, in Example 9, the particle size of the magnetic particles is reduced to 2 μm, and the dosage of the dispersant is increased to 0.9 parts; the specific surface area of the small-sized particles increases, and the formation speed of the magnetic chains accelerates. The shear stress at 800 mT reaches 76.8 kPa (slightly lower than 79.1 kPa of Example 1); the increased dosage of the dispersant inhibits particle sedimentation, and the sedimentation rate after 30 days is 14.5%.

[0081] Compared with Example 1, in Example 10, the sol-gel time is extended to 6 hours, and the thickness of the coating layer increases to 100 nm; the thicker SiO 2 layer enhances the thermal expansion buffer, and the viscosity at -40 °C drops to 0.236 Pa·s; the overly thick coating layer slightly hinders the reorganization of the magnetic chains.

[0082] Compared with Example 1, in Example 11, the magnetic particles are replaced with nickel powder from carbonyl iron powder; the magnetic permeability of nickel powder is slightly lower, and the shear stress at 800 mT drops to 77.9 kPa (compared with 79.1 kPa of Example 1); the density of nickel powder is relatively high, and the sedimentation rate is 13.1% (close to 13.7% of Example 1).

[0083] In Example 12, compared with Example 1, the proportion of esters in the base carrier liquid is increased to 40% (originally 30%); the polarity of esters is enhanced to inhibit low-temperature crystallization, and the viscosity at -40°C is 0.278 Pa·s (compared with 0.273 Pa·s in Example 1); the flexibility of the ester molecular chain is optimized, and the shear stress at 800mT is 76.1 kPa (slightly lower than that in Example 1).

[0084] The core problem of Examples 5-6: the lack of dispersant or the imbalance in the original / modified particle ratio leads to a cliff-like drop in performance, which verifies the key role of the dispersant and particle ratio.

[0085] Optimization direction of Examples 9-12: By adjusting variables such as particle size, coating process, and base carrier liquid composition, the flexibility of the formulation design was verified, and all examples met the core indicators (-40°C viscosity ≤ 0.3 Pa·s, shear stress ≥ 75 kPa, sedimentation rate ≤ 15%).

[0086] The difference between Examples 9-12 and Example 1: Under the premise of maintaining basic performance, the subtle effects of different processes or components on performance are explored through single variable adjustment, providing diversified options for practical applications.

[0087] Example 13: The weight parts are the same as those in Example 1, but the preparation method is changed: the difference is that the aerogel coating time is shortened to 3 hours (originally 5 hours), and the precursor ratio is adjusted to 1:5 (carbonyl iron powder: SiO 2 Precursor); coating thickness: 50 nm (originally 80 nm).

[0088] Example 14: The weight parts are the same as those in Example 1, but the preparation method is changed: the fluorinated silane grafting time is extended to 4 hours (originally 2 hours), and the grafting temperature is maintained at 150°C; the silane concentration is 5 vol% (originally 3.5 vol%).

[0089] Example 15: The weight parts are the same as those in Example 1, but the preparation method is changed: Step b: The precursor is replaced with MTES, and hydrolysis and condensation are carried out under acidic conditions (pH=4 adjusted with hydrochloric acid), the aging time is still 24 hours, and the porosity is 85%.

[0090] Example 16: The weight parts are the same as those in Example 1, except that the composition ratio of the base carrier liquid is modified to be: 30% mineral oil + 20% dimethyl silicone oil + 30% pentaerythritol ester + 20% PAO6; the preparation method remains unchanged.

[0091] Example 17: The weight parts are the same as those in Example 1, but the preparation method is changed: the gas phase grafting temperature is changed to 120°C, and other conditions remain unchanged.

[0092] Example 18: The weight parts are the same as those in Example 1, and the preparation method is changed: the gas-phase grafting temperature is modified to 135 °C, and other conditions remain unchanged.

[0093] Perform actual sedimentation tests on the magnetorheological fluids prepared in Examples 13 to 18, and the test results are shown in Table 4 below.

[0094] Table 4

[0095] Compared with Example 1, in Example 13, due to the thinning of the coating layer, the thermal expansion buffering ability is reduced, resulting in a slightly higher sedimentation rate than that in Example 1 (14.8% vs 13.7%); the 800 mT shear stress remains at 78.5 kPa (compared with 79.1 kPa in Example 1), and the performance difference is negligible.

[0096] Compared with Example 1, in Example 14, a higher silane concentration and a longer grafting time increase the contact angle, enhance the hydrophobicity, and reduce the sedimentation rate (12.5% vs 13.7%); the shear stress increases to 80.6 kPa (79.1 kPa in Example 1), and the optimized interfacial lubricity promotes the reorganization of particle chains.

[0097] Compared with Example 1, in Example 15, the precursor and the catalytic system are changed: the SiO generated by MTES 2 aerogel has a slightly lower porosity (85% vs 90%), resulting in a slightly higher low-temperature viscosity; the sedimentation rate is 15.6% (compared with 13.7% in Example 1), and the reduced porosity weakens the particle dispersion stability.

[0098] Compared with Example 1, in Example 16, the low-temperature fluidity of the mineral oil is slightly inferior to that of pure silicone oil, resulting in an increase in the viscosity at -40 °C from 0.273 Pa·s to 0.291 Pa·s, but still meeting the core index of ≤0.3 Pa·s; the lubricity of the mineral oil is slightly poor, and the 800 mT shear stress drops from 79.1 kPa to 77.9 kPa, but is still within the qualified range (≥75 kPa); the matching of the mineral oil density and the particles is slightly low, and the 30-day sedimentation rate increases from 13.7% to 14.2%, but there is no significant deterioration; the introduction of the mineral oil can reduce the cost, and at the same time, by adjusting the ratio of the mineral oil to the silicone oil (such as 20% mineral oil + 50% silicone oil), it may further balance the performance and economy.

[0099] Compared with Example 1, in Examples 17 and 18 respectively, the decrease in the grafting temperature causes a change in the contact angle and a slightly lower viscosity at -40 °C; the interfacial bonding force is enhanced, the sedimentation rate is increased, and the hydrophobicity improvement inhibits particle agglomeration.

[0100] Shortening the coating time or replacing the precursor can reduce costs, but the anti-settling property and fluidity need to be balanced; strengthening the grafting process (Example 14) significantly improves the hydrophobicity and magnetic response performance, which is an optimal solution for high-performance scenarios; component adjustment (Example 16): partially replacing silicone oil with mineral oil can reduce the raw material cost while maintaining the core performance indicators, which is suitable for cost-sensitive application scenarios; changing the gas-phase grafting temperature results in changes in hydrophobicity.

[0101] All examples meet the requirements of viscosity ≤ 0.3 Pa·s, shear stress ≥ 75 kPa, and sedimentation rate ≤ 15% at -40°C, demonstrating the flexibility and reliability of the formulation design.

[0102] The above are all preferred embodiments of this application. The protection scope of this application is not limited thereby. Therefore, all equivalent changes made according to the structure, shape, and principle of this application shall be covered within the protection scope of this application.

Claims

1. A low temperature resistant magnetorheological fluid, characterized in that: The invention is prepared from the following components in parts by weight: 60-75 parts of magnetic particles; 3-15 parts of modified magnetic particles; 10-25 parts of low-temperature carrier liquid, comprising 40-60% of silicone oil and / or mineral oil, 20-30% of synthetic ester, and 10-20% of poly-α-olefin; 0.1-1.0 parts of dispersant; and 0.5-2.0 parts of anticoagulant. The modified magnetic particles are obtained by coating magnetic particles with SiO2 aerogel and grafting with fluorine-containing silane.

2. The low temperature resistant magnetorheological fluid according to claim 1, characterized in that: The SiO2 aerogel coating thickness of the modified magnetic particles is 50 to 100 nm.

3. The low temperature resistant magnetorheological fluid according to claim 1, characterized in that: The dispersant is selected from polyether-modified siloxane or hyperbranched polyester amide.

4. The low temperature resistant magnetorheological fluid according to claim 1, characterized in that: The anticoagulant is selected from alkyl naphthalene derivatives or polymethacrylate.

5. The low temperature resistant magnetorheological fluid according to claim 1, characterized in that: The particle size of the magnetic particles is 0.5-10 μm, and the magnetic particles are selected from at least one of carbonyl iron powder, cobalt powder and nickel powder.

6. The low temperature resistant magnetorheological fluid according to claim 1, characterized in that: The contact angle of the fluorine-containing silane grafted modified magnetic particles is ≥110°.

7. A method for preparing a low-temperature resistant magnetorheological fluid according to any one of claims 1 to 6, characterized in that: The following steps are involved: a. Immerse the magnetic particles in silane coupling agent ethanol solution, ultrasonicate for 30 minutes, and dry at 80°C; b. Add SiO2 aerogel to the magnetic particles obtained in step a, stir at a constant temperature of 50-60°C for 4-6 hours, age for 24 hours, and then supercritically dry to form a SiO2 aerogel coating layer; c. In a vacuum reaction vessel, introduce fluorinated silane into the magnetic particles with SiO2 aerogel coating obtained in step b, and perform vapor phase grafting at 120-150°C for 2-4 hours to obtain modified magnetic particles; d. Take 10 to 25 parts by weight of the base carrier liquid and 0.5 to 2.0 parts by weight of the anticoagulant, and mix them ultrasonically at 40 to 60°C for 30 minutes to form a mixed solution; e. Take 3 to 15 parts by weight of modified magnetic particles, 0.1 to 1.0 parts of dispersant, and 60 to 75 parts of magnetic particles, mix them with the mixed solution prepared in step d, and disperse them using a microfluidizer; f. The liquid obtained in step e is subjected to a gradient cooling treatment to obtain a magnetorheological fluid.

8. The preparation method according to claim 7, characterized in that: In step f, a three-stage gradient cooling of 25°C, -20°C, and -40°C is adopted, and each stage is kept warm for 2 hours.

9. The preparation method according to claim 7, characterized in that: In step e, 60 to 75 parts of the magnetic particles are selected from the magnetic particles treated in step a.

10. The preparation method according to claim 7, characterized in that When the microfluidizer is used for dispersion in step e, the shear rate is ≥10^4 s -1 , pressure 1500 bar, and 3 cycles of dispersion.

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