High-mass-fraction magnetorheological fluid and preparation method thereof

Abstract

The invention belongs to the field of functional materials, and discloses a high-mass-fraction magnetorheological fluid and a preparation method thereof. The magnetorheological fluid comprises the following components in percentage by mass: 40%-50% of spherical carbonyl iron powder of 1-10 [mu] m, 2%-4% of a composite thixotropic agent, 0.5%-1% of a surface modified molybdenum disulfide nanosheet anti-wear agent, 1%-2% of a surfactant, 0.1%-0.2% of a small molecular surface energy regulator, 0.5%-2% of an organic gelator and the balance of carrier fluid. The preparation method comprises the following steps: performing dry mechanical fusion on the magnetic particles, the thixotropic agent, the anti-wear agent and the surfactant under the protection of inert gas, and introducing the small molecule regulator before ball milling to form core-shell structure composite powder; and adding the powder into a preheated carrier liquid containing an organic gelator in batches, shearing and dispersing, cooling to trigger in-situ gelation, and finally, carrying out vacuum defoaming to obtain the product. Through cooperation of the components and the process, the settling resistance, redispersibility and wear resistance of the magnetorheological fluid are remarkably improved, and the problems that the magnetorheological fluid is prone to hardening and rapid in performance attenuation under high concentration are solved.

Description

Technical Field

[0001] This invention belongs to the field of functional materials, specifically a high-quality fractional magnetorheological fluid and its preparation method. Background Technology

[0002] Magnetorheological fluids, as a type of intelligent fluid material, are based on the principle of controlling the aggregation state of magnetic particles by applying an external magnetic field, thereby achieving rapid and reversible changes in the rheological properties of fluids such as viscosity and shear stress. Therefore, they are widely used in fields such as automotive shock absorption systems, precision mechanical dampers, robot joint control, and hydraulic transmission devices.

[0003] The strength of the magnetorheological effect (such as shear stress and yield strength) directly depends on the number of magnetic particles per unit volume of the magnetorheological fluid. Therefore, high-quality fractional magnetorheological fluids have become a key focus of industry research. However, traditional preparation processes often employ a wet method of "mixing first and then dispersing," which suffers from persistent problems such as uneven micro-dispersion, agglomeration, sedimentation, and particle compaction, severely affecting the product's resistance to sedimentation, redispersibility, and rheological properties.

[0004] To improve the settling problem, existing technologies have attempted to add thixotropic agents (such as single-phase gaseous agents). (Or organic bentonite), but due to the "simple mixing" process, the thixotropic agent cannot form a tight interfacial bond with the magnetic particles. It can only form a loose adsorption layer on the particle surface, which is easy to fall off during dynamic shearing or temperature changes. At the same time, the existing technology lacks a long-term fixation mechanism for the dispersed particles. Even if the dispersion is uniform in the short term, the imbalance of the forces between the particles will still cause stratification during long-term use. It cannot meet the long-term stability requirement of the magnetorheological fluid for "no obvious sedimentation after standing for more than 90 days" and greatly limits its application in environments that require long-term standby or outdoor environments.

[0005] In dynamic operating conditions (such as damper piston movement and clutch friction pair transmission), magnetorheological fluids cause continuous friction and wear between magnetic particles and equipment components, as well as between the particles themselves. Current research and development focuses primarily on dispersibility and magnetic responsiveness, often neglecting wear-resistant design—neither modifying the surface of the magnetic particles for wear resistance nor adding dedicated anti-wear components. This leads to fine powder formation from particle wear during long-term use, which not only disrupts the stability of the magnetorheological effect but also exacerbates wear on equipment components, shortens the shared service life of the magnetorheological fluid and the equipment, and increases maintenance costs.

[0006] Existing magnetorheological fluid preparation processes have two major drawbacks: First, some processes rely on solvent-assisted wet coating, requiring an additional solvent removal step, which not only prolongs the production cycle and increases energy consumption, but may also affect product performance due to solvent residue; Second, the mixing and dispersion processes lack precise control (such as the absence of inert gas protection and low matching degree between shear rate and temperature), resulting in magnetic particles being easily oxidized and thixotropic agents being unevenly dispersed. Ultimately, this leads to large fluctuations in sedimentation rate and magnetic response performance between different batches of products, making it difficult to meet the consistency requirements of large-scale industrial applications.

[0007] Magnetorheological fluids are often used in applications that involve temperature fluctuations (such as automotive shock absorption systems which need to withstand ambient temperature changes from -30℃ to 80℃). However, the viscosity of the carrier fluids used in existing technologies (such as ordinary mineral oil) is highly sensitive to temperature, easily solidifying at low temperatures and thinning at high temperatures. At the same time, traditional stabilizers or gel systems have a narrow temperature range, and temperature changes can cause the gel network to break or shrink excessively, further aggravating the sedimentation and aggregation of magnetic particles. This prevents the magnetorheological fluid from working properly at extreme temperatures, limiting its application in complex environments such as outdoor and high-temperature equipment.

[0008] Therefore, there is an urgent need for a magnetorheological fluid technology that can further improve the quality fraction, anti-settling properties and redispersibility, in order to meet the demand of various fields for intelligent fluid materials with high stability, long life and strong environmental adaptability. Summary of the Invention

[0009] The present invention aims to at least partially solve one of the technical problems in the related art.

[0010] This invention improves the long-term stability, redispersibility, wear resistance, and consistency of magnetorheological fluids by innovating the design of a synergistic component system of magnetic particles, composite thixotropic agents, surfactants, and small molecule surface energy modifiers, and by employing a two-stage mechanical fusion coating and in-situ gelation fine dispersion preparation method. It also alleviates the problems of magnetic particle agglomeration, easy detachment of coating layers, and performance degradation during dynamic use in traditional magnetorheological fluids. At the same time, it provides a method for preparing high-quality fractional magnetorheological fluids.

[0011] The purpose of this invention is to provide a high-quality fractional magnetorheological fluid, characterized by comprising the following components by mass fraction: 40% to 50% magnetic particles; said magnetic particles are 1-10 μm spherical carbonyl iron powder; 2% to 4% composite thixotropic agent; said composite thixotropic agent is derived from gas phase... It consists of organic bentonite and organic bentonite, each accounting for 1%-2% of the total mass of the final product; 0.5% to 1% anti-wear agent; 1% to 2% surfactant; 0.1% to 0.2% small molecule surface energy modifier; 0.5% to 2% organic gelling agent; and the balance being carrier liquid; The composite thixotropic agent, surfactant, small molecule surface energy modifier, and anti-wear agent are synergistically coated onto the surface of the carbonyl iron powder through a mechanical fusion process, forming a core-shell structured composite powder. The composite powder is dispersed in a carrier liquid containing the organic gelling factor and is immobilized by a three-dimensional gel network formed by the self-assembly of the organic gelling factor. The organic gelling factor is a small molecule or oligomer capable of reversibly self-assembling into a three-dimensional network structure in the carrier liquid through temperature changes, and is selected from: fatty acids and their derivatives, steroidal compounds, and amino acid derivatives.

[0012] Furthermore, the anti-wear agent is surface-modified molybdenum disulfide nanosheets, using silane coupling agents, surfactants, or polyvinylpyrrolidone as surface modifiers for molybdenum disulfide, and performing surface modification through chemical grafting, physical adsorption, sol-gel coating, or other methods.

[0013] Furthermore, the surfactant is an octenyl succinic anhydride-grafted polyethyleneimine or a polyamide-amine dendritic macromolecule; the small molecule surface energy modifier is an organic compound with a molecular weight of less than 1500 containing ether bonds, hydroxyl groups, amine groups or ester groups, selected from: polyether compounds, fatty acid ester nonionic surfactants, silane or titanate coupling agents.

[0014] Furthermore, the organic gelling agent is dodecyl stearic acid; the carrier liquid is a base oil, which is a modified silicone oil or a synthetic hydrocarbon base oil. The carrier liquid also contains 0.01% to 0.5% polyether polyol dispersant by weight of the final product.

[0015] Furthermore, the three-dimensional gel network is an elastic fiber network that runs through the entire liquid carrier system and is formed by the self-assembly of the organic gelling factor triggered by temperature changes.

[0016] The aforementioned magnetic particles provide the basis for magnetic response, forming a chain-like structure under an applied magnetic field, generating shear yield stress. The narrow spherical particle size distribution (1-10 μm) reduces interparticle frictional resistance and lowers the zero-field viscosity (0.93-0.97 Pa·s), while ensuring a sufficient number of particles per unit volume (mass fraction 40-50%), thus enhancing magnetic flux density. Compared to the conventional 20-40% mass fraction, this scheme addresses the high-concentration sedimentation problem through surface energy modulation, improving magnetic response performance by over 20%.

[0017] The gas phase of the above-mentioned composite thixotropic agent The nanoscale particles form a physical barrier, increasing steric hindrance between particles and inhibiting aggregation; the organobentonite absorbs water and swells to form a hydrogen bond network, constructing a weak gel structure in the carrier liquid, which hinders particle sedimentation when static. The synergistic effect of the two is significant, and the sedimentation inhibition efficiency is improved by 30% compared with that of a single thixotropic agent.

[0018] The layered structure of the aforementioned anti-wear agent MoS2 nanosheets slides during shearing, reducing interparticle friction; in dynamic wear tests, particle wear is reduced by 57%, and the lifespan of equipment components is extended by 2 times.

[0019] The hydrophilic / lipophilic groups at both ends of the surfactant anchor the hydroxyl groups on the iron powder surface, forming "molecular bridges," reducing the surface energy of the particles, and making the thixotropic agent coating more uniform. The small molecule surface energy modifier fills the "high-energy defect points" (such as the edges of iron powder) generated during ball milling, reducing the local surface energy through physical adsorption (van der Waals forces) and inhibiting secondary agglomeration.

[0020] The aforementioned organic gelling agents form a gel network, which, after dissolving at 60-70℃ and cooling, self-assembles into a three-dimensional fiber network, physically locking the composite powder and achieving a static sedimentation inhibition rate of 97%. The base oil viscosity and gelling agents work synergistically to balance zero-field flowability (low viscosity) and dynamic locking ability (high network strength), improving the temperature stability of the carrier fluid by 25% compared to pure silicone oil.

[0021] The present invention also aims to provide a method for preparing a high-quality fractional magnetorheological fluid, characterized by comprising the following steps: S1. Composite powder preparation: The micron-sized spherical carbonyl iron powder, composite thixotropic agent, anti-wear agent and surfactant are mechanically fused under inert gas protection. Ten minutes before the end of ball milling, a small molecule surface energy modifier is introduced by atomization spraying or airflow introduction. Ball milling continues until the end of the process, so that each component is synergistically coated on the surface of carbonyl iron powder to form a core-shell structured composite powder. S2. In-situ gelation and dispersion: The composite powder obtained in step S1 is slowly added in multiple portions to a carrier liquid pre-dispersed with organic gelling agents and polyether polyol dispersants. The mixture is first sheared and mixed uniformly at 1000 r / min at 60-70℃, and then cooled to room temperature in a gradient manner to trigger the self-assembly of organic gelling agents to form a three-dimensional gel network and fix the composite powder. The cooling rate is 0.5℃ / min to 2℃ / min. S3. Vacuum degassing treatment: Vacuum degassing is performed on the mixture cooled in step S2 to obtain the magnetorheological fluid.

[0022] Furthermore, in step S1, the mechanical fusion process uses a high-speed energy ball mill or a mechanical fusion machine, with a processing speed of 300 r / min to 500 r / min and a processing time of 30 min to 120 min.

[0023] Further, the composite powder obtained in step S1 is divided into three equal parts in advance. The carrier liquid temperature is kept at 65°C. The first part of the composite powder is slowly added at a shear rate of 1000 r / min. The system is slowly cooled to 60°C at a cooling rate of about 1°C / min. The shear rate is maintained, and the second part of the composite powder is added. The system is further cooled to 55°C at a cooling rate of about 1°C / min. The shear rate is maintained, and the last part of the composite powder is added. After all the materials are added, heating is stopped, and the system is allowed to cool slowly to room temperature at a rate of about 0.5-2°C / min.

[0024] Furthermore, in step S3, the vacuum degassing conditions are: degassing for 20 minutes at a vacuum of -0.08 MPa.

[0025] Furthermore, after step S1, the obtained composite powder is passed through a 600-mesh sieve to remove large particles and agglomerates; the final product is sealed with argon gas and stored in a dry environment below 25°C.

[0026] In the above method, the preparation of S1 composite powder adopts a two-stage mechanical fusion. In the first stage, amphoteric molecules preferentially anchor to the iron powder surface to form a chemisorption layer (CO-Fe bonds), providing "anchor points" for the thixotropic agent and solving the "point contact" defect of traditional coating. In the second stage, a small molecule surface energy modifier is added 10 minutes before the end. The modifier is adsorbed at a low speed (300 r / min) at the end of the ball milling process to avoid high speed destroying its weak interaction forces, repairing high-energy areas (such as new surfaces generated by iron powder breakage), and forming a "dense-loose" gradient coating layer.

[0027] In the above method, S2 is in-situ gelled and dispersed. During the first cooling process from 65℃ to 60℃, the carrier liquid has been preheated to 65℃, and the organic gelling agents (such as dodecyl stearic acid) have completely dissolved, with the molecules in a highly extended and active state. The temperature decreases, reducing the thermal mobility of the gelling agent molecules, and intermolecular forces (such as hydrogen bonds) begin to dominate, driving them to spontaneously aggregate and assemble into fibrous "nuclei" or short chains. These initial network structures use the first batch of added powder particles as "anchors," initially forming a scaffold-like network framework that runs through the system. Initial dispersion at high temperature and low viscosity minimizes resistance and effectively prevents powder agglomeration upon initial addition, laying the crucial foundation for the uniformity of the entire system. The relatively slow cooling rate avoids "explosive" rapid nucleation of the gelling agents, resulting in a moderate number and uniform distribution of network "nuclei," preventing localized over-density or clumping. Dispersing the first batch of particles under high fluidity conditions before triggering initial gelation ensures the orderly construction of the network framework under undisturbed conditions.

[0028] During the second cooling process, from 60℃ to 55℃, the system is already at 60℃ and has formed a preliminary gel network framework. The viscosity of the system has increased significantly compared to the first stage. Under constant temperature and continuous shear at 60℃, the second part of the composite powder is added. At this time, the existing weak network structure is temporarily partially destroyed by the shear force, but it provides a higher viscosity environment for the dispersion of the new powder and reduces the sedimentation rate. After uniform dispersion, the temperature is lowered again to 55℃ at a rate of about 1℃ / min. The new gelling factor molecules will continue to extend, connect, and intertwine based on the already formed "network framework." The newly added powder particles are encapsulated in this growing network. This stage is a critical period for the full development, penetration, and strengthening of the three-dimensional network structure, and the density and strength of the network increase significantly. The second network interweaves and entangles with the first network, forming a denser and more stable composite gel structure, whose uniformity and strength far exceed those of a network formed in one step.

[0029] In the third cooling stage, from 55℃ to room temperature, the final portion of the composite powder is added and dispersed at 55℃. At this point, the system has clearly gelled, and its fluidity is greatly reduced. After all materials are evenly dispersed, heating is stopped, and the system is allowed to cool slowly to room temperature at a natural or controlled rate (approximately 0.5-1℃ / min). Gentle stirring is maintained throughout the process to prevent unevenness caused by thermal convection. This stage primarily involves the final solidification and stabilization of the gel network. As the temperature further decreases, molecular thermal motion continues to weaken, and intermolecular forces such as hydrogen bonds between gel fibers reach their strongest point. The entire three-dimensional network structure is thoroughly tightened and shaped, firmly locking all magnetic particles within its mesh. The slow final cooling provides the gel network with sufficient time for molecular-level adjustment and relaxation, releasing internal stress and forming a more thermodynamically stable and elastic network structure, rather than a brittle structure. By controlling the cooling rate in the final stage, the micromechanical properties (such as elasticity and reversibility) of the gel network were actively optimized, making it strong in static locking and easy to break and recover under shear, thus possessing both excellent anti-settling and redispersibility.

[0030] In the above method, the S3 vacuum degassing step eliminates bubbles introduced by shear mixing, prevents bubbles from becoming sedimentation initiation points, removes undispersed large agglomerates (>200μm), and ensures the consistency of particle size in the final product.

[0031] One of the core mechanisms of this invention lies in the mechanical fusion process that enables a dense composite coating layer to be formed on the surface of magnetic particles by combining a composite thixotropic agent, surfactant, anti-wear agent, and small molecule surface energy modifier. This process is not a simple physical mixing of components, but follows a specific sequence and mechanism of action: First, surfactant molecules preferentially anchor to active sites such as hydroxyl groups on the surface of magnetic particles through their polar groups, forming a robust chemisorption layer. This layer acts as a "molecular bridge," providing a foundation for the subsequent adhesion of other components. Then, the composite thixotropic agent (vaporized SiO2 and organic bentonite) is constructed on this adsorption layer through steric hindrance and hydrogen bonding, forming a nanoscale physical barrier and a weak gel structure on the particle surface, respectively, effectively inhibiting close-range aggregation between particles. The anti-wear agent (such as surface-modified molybdenum disulfide nanosheets) is simultaneously integrated into this coating layer, enabling it to directly exert its friction-reducing and anti-wear effects under dynamic working conditions. Specifically, small-molecule surface energy modifiers are introduced at the end of the mechanofusion process. Their function is to selectively adsorb onto high-energy regions such as surface lattice defects or edges generated by mechanical forces, thereby fundamentally eliminating the driving force leading to secondary aggregation by reducing local surface energy. Ultimately, the core-shell structure formed through mechanochemical forces exhibits higher uniformity, density, and stability compared to traditional physical adsorption coatings, and the coating layer is less prone to detachment.

[0032] To address the problem of long-term sedimentation, this invention employs in-situ gelation fixation technology. The aforementioned composite powder is dispersed in a carrier liquid containing an organic gelling agent (such as dodecyl stearic acid). During the process, the organic gelling agent molecules are first heated (e.g., to 60-70°C) to allow them to fully expand and dissolve in the carrier liquid. Subsequently, the mixture is cooled to room temperature under shear dispersion. This temperature change triggers the self-assembly behavior of the organic gelling agent, whose molecules spontaneously aggregate, grow, and entangle with each other through intermolecular forces such as hydrogen bonds and van der Waals forces, forming a three-dimensional fibrous gel network that permeates the entire carrier liquid system. This network physically "locks" the interface-coated magnetic particles within its grid, significantly restricting the free sedimentation path of the particles. Compared to traditional thixotropic agents that rely solely on increasing system viscosity to slow sedimentation, this three-dimensional gel network is reversible: it provides strong locking ability under static conditions, while the network structure can be temporarily disrupted when external shear forces (such as shaking or working shear) are applied, restoring the system's fluidity. Once the shearing stops, the network can reform. This characteristic gives magnetorheological fluids both excellent anti-settling properties and good fluidity (low apparent viscosity).

[0033] Each step of this preparation method is precisely controlled to address the characteristics of a high-quality fractional system. The principle behind this method is to minimize instability introduced into the process. The composite powder preparation stage is conducted under inert gas protection to isolate oxygen and prevent oxidation of magnetic particles during mechanical fusion, thus ensuring the stability of magnetic properties. A two-stage addition strategy is employed to ensure that components with different functions are coated at the optimal time and energy conditions for their respective mechanisms of action. This prevents small-molecule regulators from being destroyed or prematurely desorbed during high-speed, high-energy stages, thereby ensuring the integrity and gradient of the coating layer. In the in-situ gelation and dispersion stage, the composite powder is slowly added to the premixed carrier liquid in multiple portions. This is to control the local concentration and prevent irreversible agglomeration caused by excessively high concentrations in local eddy zones due to adding too much powder at once. Combined with the steric hindrance effect of the polyether polyol dispersant, uniform particle dispersion is achieved. Subsequent measures such as sieving, vacuum degassing, and inert gas sealing storage are designed to remove large agglomerates generated during the process, eliminate bubbles that may become the starting point for sedimentation, and isolate the finished product from moisture and oxygen during storage. These measures ensure that the final product has highly consistent performance and excellent long-term stability across different batches.

[0034] Beneficial effects: 1. The synergistic effect of composite thixotropic agents, surfactants, and small-molecule surface energy modifiers, combined with a two-stage mechanical fusion coating process, forms a uniform and dense core-shell structure on the surface of magnetic particles. This, combined with a three-dimensional gel network self-assembled by organic gelling agents, significantly suppresses particle aggregation in the magnetorheological fluid, preventing caking after standing. Compared to the tendency of traditional magnetorheological fluids to settle, this method requires no high shear force and achieves uniform redispersibility of the magnetorheological fluid through simple operation, resulting in significantly improved stability during storage and use.

[0035] 2. High-quality, fractional-micron-sized spherical carbonyl iron powder provides a sufficient foundation for the magnetorheological effect. Combined with the synergistic optimization of the interfaces of each component, the magnetic particles can quickly form a stable chain structure under an applied magnetic field, significantly enhancing the sensitivity and stability of the magnetic response performance, meeting the precision requirements of magnetic control in precision equipment. The surface-modified molybdenum disulfide nanosheet anti-wear agent is compatible with other components, effectively reducing frictional losses between particles and between particles and equipment components during dynamic operation. This maintains the long-term stability of the magnetorheological effect and extends the service life of the magnetorheological fluid and the applied equipment.

[0036] 3. Optimized processes such as composite powder sieving, batch feeding, and precise temperature control during preparation effectively reduce performance fluctuations between different batches, ensuring batch consistency in industrial production. The compatible design of the carrier liquid and organic gelling agent, inert gas protection, and argon-sealed storage of the finished product enable the magnetorheological fluid to maintain stable viscosity and structure over a wide temperature range, avoiding the performance failure problems of traditional magnetorheological fluids caused by environmental temperature changes. This makes it suitable for applications in various fields such as automotive shock absorption and precision mechanical damping. Detailed Implementation

[0037] Various exemplary embodiments of the present invention will now be described in detail. This detailed description should not be considered as a limitation of the present invention, but rather as a more detailed description of certain aspects, features, and embodiments of the present invention.

[0038] With regard to numerical ranges in this invention, it should be understood that each intermediate value between the upper and lower limits of the range is also specifically disclosed. Every smaller range between any stated value or intermediate value within a stated range, and any other stated value or intermediate value within said range, is also included in this invention. The upper and lower limits of these smaller ranges may be independently included or excluded from the range.

[0039] Unless otherwise stated, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art. While only preferred methods and materials have been described herein, any methods and materials similar or equivalent to those described herein may be used in the implementation or testing of this invention. All references to this specification are incorporated by way of citation to disclose and describe methods and / or materials associated with those references. In the event of any conflict with any incorporated reference, the content of this specification shall prevail.

[0040] Various modifications and variations can be made to the specific embodiments described in this specification without departing from the scope or spirit of the invention, as will be apparent to those skilled in the art. Other embodiments derived from this specification will also be apparent to those skilled in the art. This specification and embodiments are merely exemplary.

[0041] The terms “include,” “including,” “have,” “contain,” etc., used in this article are all open-ended terms, meaning that they include but are not limited to.

[0042] For experiments not specifically described in the examples, the procedures or conditions should be followed according to the conventional experimental procedures described in the literature in this field. Reagents or instruments whose manufacturers are not specified are all commercially available conventional reagent products.

[0043] All examples below are expressed as mass fractions unless otherwise specified.

[0044] Example 1 This embodiment provides a high-quality fractional magnetorheological fluid and its preparation method.

[0045] Formula composition: Micron-sized spherical carbonyl iron powder (particle size 1-10μm): 45% Composite thixotropic agent: 3% (of which the gas phase) (1.5% of the total content is organic bentonite) Anti-wear agent (surface-modified molybdenum disulfide nanosheets): 0.8% Surfactant (octenyl succinic anhydride grafted polyethyleneimine): 1.5% Small molecule surface energy modifier (polyethylene glycol monomethyl ether): 0.15% Organic gelling agent (dodecyl stearic acid): 1.2% Dispersant (polyether polyol): 0.1% Carrier fluid (base oil): Balance (top up to 100%) Preparation methods include: S1. Preparation of composite powder: Carbonyl iron powder and composite thixotropic agent (gas phase) The organic bentonite, anti-wear agent (molybdenum disulfide nanosheets), and surfactant (octenyl succinic anhydride grafted polyethyleneimine) are premixed and mixed for 10 minutes under inert gas (argon) protection using a V-type mixer to ensure uniformity.

[0046] The mixed powder was fed into a high-speed energy ball mill (the volume of the grinding jar was 3-5 times the total mass of the powder, and the grinding media was zirconia balls), and ball-milled for 90 minutes at 400 r / min under argon protection. During the ball milling process, a 5-minute pause was made every 30 minutes to control the temperature rise.

[0047] Ten minutes before the end of ball milling (i.e., at the 80th minute), pause the ball mill and use an ultrasonic atomizer to evenly spray the small molecule surface energy modifier (polyethylene glycol monomethyl ether, dissolved in 5 mL of anhydrous ethanol to prepare a 3% solution) onto the powder surface.

[0048] Reseal the ball mill jar and continue ball milling for 10 minutes to allow the small molecule regulator to be fully adsorbed.

[0049] After ball milling, the composite powder is passed through a 600-mesh sieve to remove large particles and agglomerates, resulting in a core-shell composite powder with good flowability.

[0050] S2. In-situ gelation dispersion: The composite powder obtained in step S1 is divided into three equal parts. The carrier liquid temperature is kept at 65°C. The first part of the composite powder is slowly added at a shear rate of 1000 r / min. The system is slowly cooled to 60°C at a cooling rate of about 1°C / min. The shear rate is maintained, and the second part of the composite powder is added. The system is further cooled to 55°C at a cooling rate of about 1°C / min. The shear rate is maintained, and the last part of the composite powder is added. After all the materials are added, heating is stopped, and the system is allowed to cool slowly to room temperature at a rate of about 0.5-2°C / min.

[0051] S3. Vacuum degassing treatment: The cooled mixture was degassed for 20 minutes under a vacuum of -0.08 MPa to remove air bubbles.

[0052] The final product is sealed with argon gas and stored in a dry environment below 25°C.

[0053] The magnetorheological fluid obtained in this embodiment has a sedimentation rate of only 2.3% after standing for 90 days, with no caking phenomenon. It can be redispersed evenly after 10 gentle shakes, with a yield stress of 180 Pa and an apparent viscosity of 0.95 Pa·s.

[0054] Example 2 The difference from Example 1 is that the surfactant used is a polyamide-amine dendritic macromolecule (1.0% by mass), and the small molecule surface energy modifier used is hydroxypropyl methylcellulose (0.2% by mass). The preparation steps are the same as in Example 1.

[0055] Example 3 The difference from Example 1 is that the small molecule surface energy modifier was added at 45 minutes after the start of ball milling, instead of 10 minutes before the end.

[0056] Example 4 The difference from Example 1 is that the amount of organic gelling agent is increased to 1.5%, and the amount of dispersant is increased to 0.3%.

[0057] Comparative Example 1 The difference from Example 1 is that no surfactants and small molecule surface energy modifiers are added. Only iron powder, thixotropic agents, and anti-wear agents are added during ball milling.

[0058] Comparative Example 2 The difference from Example 1 is that no small molecule surface energy modifier is added; only a surfactant is added.

[0059] Comparative Example 3 The difference from Example 1 is that no surfactant is added, only a small molecule surface energy modifier is added.

[0060] Comparative Example 4 The difference from Example 1 is that the ball milling process is carried out in an air environment without inert gas protection.

[0061] The magnetic fluids obtained in Examples 1-4 and Comparative Examples 1-4 were subjected to performance tests.

[0062] All tests were conducted in a constant temperature (25±0.5℃) and constant humidity (50%±5% relative humidity) laboratory environment, and the samples were equilibrated in this environment for at least 24 hours before the test.

[0063] I. Anti-settling test: This test aims to quantify the stability of magnetorheological fluids under long-term static conditions and evaluate their ability to resist particle sedimentation and the formation of hard precipitates (caking).

[0064] 1. Preparation of testing equipment and samples: The equipment uses a graduated (minimum graduation value 0.1mL) transparent glass tube (inner diameter 25mm, height 200mm) for sedimentation testing, and a constant temperature incubator.

[0065] Sample preparation: After thoroughly shaking the final product until homogeneous, accurately measure 50 mL and inject it into the settling tube, recording the initial total volume V0. Prepare three replicates for each sample group.

[0066] 2. Test steps: Place the sealed settling tube vertically in a constant temperature incubator and let it stand at 25°C for 90 days. After the standing period, carefully remove the settling tube, avoiding any shaking. Observe and record the separation interface between the supernatant (or semi-supernatant) and the lower suspended slurry. Accurately read the volume V1 of the supernatant and calculate the settling rate using the following formula: Settling rate (%) = [(V0-V1) / V0] × 100%. Take the result as the arithmetic mean of three parallel samples.

[0067] To assess the compaction phenomenon, a 2mm diameter glass rod is inserted vertically into the bottom of the settling pipe at a constant, slow speed. If it can be easily inserted without significant hard resistance, it is recorded as "no compaction"; if significant resistance is encountered or it cannot be inserted, it is recorded as "compacted".

[0068] II. Redispersibility Test: This test assesses the ease with which a magnetorheological fluid that has settled after standing can be restored to a uniformly dispersed state after being subjected to slight external disturbance. This directly relates to the product's ease of use.

[0069] 1. Test equipment and sample preparation: The sedimentation pipes that have completed the 90-day static test.

[0070] 2. Test steps: After completing the sedimentation rate measurement, the sedimentation tube was manually shaken: at a frequency of approximately once per second, the test tube was shaken vertically 10 times (round trip counted as one time). Immediately after shaking, a visual evaluation was performed against a well-lit background. The evaluation results included: Uniform: The material inside the pipe is in a uniform suspended state with no visible particles or flocculents, and is no different from its original state.

[0071] Slight sedimentation: Most of the material has been evenly dispersed, but there is still a small amount of visible soft sediment at the bottom of the pipe, which can be dispersed by slight shaking.

[0072] Stratification / agglomeration: The material is still clearly stratified, or large flocculent clumps appear, which cannot be restored to uniformity by slight shaking.

[0073] III. Rheological property testing is used to characterize the mechanical properties of magnetorheological fluids under the action of a magnetic field, and is a key indicator for evaluating their application value as smart materials.

[0074] 1. Testing equipment: A coaxial cylindrical rotational rheometer equipped with a magnetron control unit (such as the Anton Paar MCR series or the TA Instruments DHR series) is used. A concentric cylindrical rotor suitable for suspensions with high particle content is selected.

[0075] 2. Test steps: Sample loading: Carefully load the sample, which has been allowed to stand and then gently stirred to restore homogeneity, into the measuring fixture of the rheometer, ensuring that there are no air bubbles.

[0076] Yield stress test: Under the condition of applying a specific magnetic field strength (e.g., 200 kA / m), a steady-state shear rate scan (e.g., from 0.01 s⁻¹) is performed. -1 to 100s -1 The dynamic yield stress (τ_y), in Pascals (Pa), is obtained by extrapolating from the fitted shear stress-shear rate curve (commonly the Herschel-Bulkley model).

[0077] Apparent viscosity test: Under zero magnetic field conditions (H=0), the viscosity of the sample at a fixed shear rate (100 s⁻¹) was measured. -1 The apparent viscosity (η) is calculated using the formula η = τ / γ̇, where τ is the shear stress and γ̇ is the shear rate (100 s⁻¹). -1 ), the unit is Pascal-second (Pa·s).

[0078] 3. Data Recording: Each sample was tested three times, and the arithmetic mean of the yield stress and apparent viscosity was taken as the final result.

[0079] Through the above-described systematic testing methods, the significant differences between the embodiments of the present invention and the comparative examples in terms of anti-settling properties, redispersibility, and rheological properties can be objectively and quantitatively compared, which strongly supports the technical advantages of the present invention.

[0080] IV. Wear Measurement 1. Sample pretreatment and experimental preparation Take 10 mL of the magnetorheological fluid sample to be tested and place it in a constant temperature and humidity chamber at 25±0.5℃ for 24 h to equilibrate; stir the sample slowly with a glass rod for 30 s to ensure that the sample is uniform and free of agglomeration; take 2 mL of the uniform sample for later use.

[0081] GCr15 steel balls (6mm in diameter, HRC60-62 hardness) and 45# steel discs (Ra=0.2μm surface roughness, simulating precision mechanical damping components) were selected. The balls were ultrasonically cleaned with anhydrous ethanol for 10 minutes, dried, and then weighed on an electronic balance to determine their initial mass (denoted as m0). Fix the steel disc on the worktable of the pin-disc testing machine, and evenly apply the prepared 2mL magnetorheological fluid to the friction area of ​​the steel disc (within a diameter of 10mm) to ensure that the friction surface is completely wetted by the sample (simulating the contact state between the fluid and the component in actual applications).

[0082] 2. Friction test (responding to the dynamic wear scenario of the document) Set the testing machine parameters: load 10N (medium load, covering most civilian scenarios), speed 500r / min (simulating the piston movement speed of the damper), friction radius 5mm, test time 60min (sufficient to generate quantifiable wear, avoiding data inconsistency due to excessively short test time); start the testing machine and maintain a constant temperature and humidity environment throughout the test, recording the friction torque during the test (used to assist in verifying friction stability and correlate with the effect of anti-wear agent); after the test, turn off the testing machine, remove the steel ball and steel disc, ultrasonically clean with anhydrous ethanol for 15min (to remove residual magnetorheological fluid and wear powder from the surface), place in a 60℃ oven to dry for 30min, and cool to room temperature.

[0083] 3. Wear Measurement 4. Measurement of mass wear: The cooled steel ball is weighed on a high-precision electronic balance and recorded as follows. Calculate the mass loss of the steel ball. = - Simultaneously, take 1 mL of the residual magnetorheological fluid after friction, filter it through a 0.22 μm filter membrane (to trap fine powder generated by abrasion), dry the filter membrane, weigh it, and record the weight as follows: (Initial filter membrane mass is m) 滤 ), calculate the mass of fine powder from particle wear = - ; Volumetric wear verification: The filtered fine powder was scanned with a laser particle size analyzer, and the particle size distribution was recorded (if fine powder <1μm appears, it is considered wear product). This was combined with the fine powder density (carbonyl iron powder density 7.86g / cm³). 3 ), calculate the volumetric wear of fine powder = / 7.86 (Supplementing the reliability of wear and tear data to avoid bias from a single indicator).

[0084] The test results are shown in Table 1 below.

[0085] The above samples were tested, and the results are shown in the table below: Table 1. Performance test results of the examples and comparative examples. The anti-settling, redispersibility, and rheological properties of the magnetorheological fluid samples from Examples 1-4 and Comparative Examples 1-4 were tested (test conditions: constant temperature of 25±0.5℃, constant humidity of 50%±5%, sample equilibration for more than 24 hours). The results showed that the magnetorheological fluid prepared by this invention (such as Examples 1-4) is significantly superior to traditional technical solutions (such as Comparative Examples 1-4) in terms of core performance. Specifically, in terms of anti-settling, the sedimentation rate of the sample from the examples after 90 days of static settling was only 2.0%-2.8%, with no caking phenomenon. It could be restored to a uniform dispersion state after 10 vertical shakings. In contrast, the sedimentation rate of the comparative examples was as high as 4.2%-7.5%, and some samples showed caking and slight precipitation or stratification after redispersibility. This difference fully demonstrates the effectiveness of the "synergistic coating of composite thixotropic agent, surfactant, and small molecule surface energy modifier" and the "mechanical fusion (inert gas protection, addition of modifier in the middle and later stages) combined with in-situ gelation dispersion" process in this invention. This can be achieved through steric hindrance, hydrogen bond network, and The three-dimensional gel network synergistically inhibits particle agglomeration and sedimentation, solving the industry pain point of easy caking of traditional magnetorheological fluids at high concentrations. In terms of rheological properties, the yield stress of the sample in the example reached 175-185 Pa, and the zero-field apparent viscosity was 0.93-0.98 Pa·s, achieving a balance between "high magnetic responsiveness and low zero-field viscosity". In contrast, the comparative sample had a yield stress of only 158-170 Pa and an abnormally low apparent viscosity due to particle agglomeration or oxidation. This result confirms that the present invention not only ensures the magnetic flux density per unit volume to enhance the magnetorheological effect, but also reduces the viscosity by reducing inter-particle friction through narrow particle size distribution. At the same time, the process of batch feeding and 600-mesh sieve removal of agglomerates ensures uniform particle dispersion. In addition, the test results of Examples 2, 3 (adjusting the timing of the regulator addition) and 4 all maintained excellent performance, further demonstrating that the range of selectable components and process parameters defined in the claims of the present invention has good flexibility and can be adapted to different production needs while ensuring stable performance.

[0086] Specifically, if the cooling rate exceeds 2°C / min, the thermal motion of the gelling agent molecules is suddenly restricted, preventing them from fully expanding and orderly entangled through hydrogen bonds and van der Waals forces. This easily leads to the formation of localized agglomerates or broken gel networks, resulting in some composite powders not being effectively locked in, increasing the risk of sedimentation. In the comparative examples, where the cooling rate was not controlled (implying rapid cooling), some samples showed caking, essentially indicating an uneven gel network. If the cooling rate is below 0.5°C / min, the carrier liquid viscosity rises slowly, and the composite powder (especially carbonyl iron powder with a mass fraction of 40%-50%) is prone to premature sedimentation and agglomeration due to gravity before the gel network is fully formed, disrupting the dispersion uniformity. However, a cooling rate range of 0.5°C / min to 2°C / min allows the gelling agent molecules to "gradually and orderly self-assemble" simultaneously with the "slow rise in carrier liquid viscosity," ultimately forming a defect-free, fully covered three-dimensional network. The absence of caking in Examples 1-4 directly demonstrates this advantage.

[0087] In summary, this invention, through component synergistic design and process innovation, effectively improves the long-term stability, redispersibility, and magnetic response performance of magnetorheological fluids, completely alleviating the defects of traditional technologies such as easy sedimentation at high concentrations, rapid performance degradation, and insufficient wear resistance, thus meeting the application requirements of high-quality fractional magnetorheological fluids in fields such as automotive shock absorption and precision mechanical damping.

[0088] Furthermore, the terms "first" and "second" are used for descriptive purposes only and should not be construed as indicating or implying relative importance or implicitly specifying the number of technical features indicated. Thus, a feature defined as "first" or "second" may explicitly or implicitly include at least one of that feature. In the description of this invention, "a plurality of" means at least two, such as two, three, etc., unless otherwise explicitly specified.

[0089] In the description of this specification, the references to terms such as "one embodiment," "some embodiments," "example," "specific example," or "some examples," etc., indicate that a specific feature, structure, material, or characteristic described in connection with that embodiment or example is included in at least one embodiment or example of the present invention. In this specification, the illustrative expressions of the above terms do not necessarily refer to the same embodiment or example. Furthermore, the specific features, structures, materials, or characteristics described may be combined in any suitable manner in one or more embodiments or examples. Moreover, without contradiction, those skilled in the art can combine and integrate the different embodiments or examples described in this specification, as well as the features of different embodiments or examples.

[0090] Although embodiments of the present invention have been shown and described above, it is understood that the above embodiments are exemplary and should not be construed as limiting the present invention. Those skilled in the art can make changes, modifications, substitutions and variations to the above embodiments within the scope of the present invention.

Claims

1. A high-quality fractional magnetorheological fluid, characterized in that, Components including the following mass fractions: 40% to 50% magnetic particles; the magnetic particles are 1-10 μm spherical carbonyl iron powder; 2% to 4% of a composite thixotropic agent; said composite thixotropic agent is derived from a gas phase It is composed of organic bentonite, with each accounting for 1%-2% of the total mass of the final product; 0.5% to 1% anti-wear agent; 1% to 2% surfactant; 0.1% to 0.2% small molecule surface energy modifier; 0.5% to 2% organic gelling agent; And the remaining carrier fluid; The composite thixotropic agent, surfactant, small molecule surface energy modifier and anti-wear agent are synergistically coated on the surface of the carbonyl iron powder through a mechanical fusion process to form a core-shell structured composite powder. The composite powder is dispersed in a carrier liquid containing the organic gelling factor and is fixed by a three-dimensional gel network formed by the self-assembly of the organic gelling factor. The organic gelling factor is a small molecule or oligomer that can reversibly self-assemble into a three-dimensional network structure in the carrier liquid by temperature change, and is selected from: fatty acids and their derivatives, steroidal compounds, and amino acid derivatives.

2. The high-quality fractional magnetorheological fluid according to claim 1, characterized in that, The anti-wear agent is surface-modified molybdenum disulfide nanosheets.

3. The high-quality fractional magnetorheological fluid according to claim 1, characterized in that, The surfactant is an octenyl succinic anhydride-grafted polyethyleneimine or a polyamide-amine dendritic macromolecule; the small molecule surface energy modifier is an organic compound with a molecular weight of less than 1500 containing ether bonds, hydroxyl groups, amine groups or ester groups, selected from: polyether compounds, fatty acid ester nonionic surfactants, silane or titanate coupling agents.

4. The high-quality fractional magnetorheological fluid according to claim 1, characterized in that, The organic gelling agent is dodecyl stearic acid; the carrier liquid is a base oil, and the carrier liquid also contains 0.01% to 0.5% of a polyether polyol dispersant by weight of the final product.

5. The high-quality fractional magnetorheological fluid according to any one of claims 1-4, characterized in that, The three-dimensional gel network is an elastic fiber network that runs through the entire carrier liquid system and is formed by the self-assembly of the organic gelling factor triggered by temperature changes.

6. A method for preparing a high-quality fractional magnetorheological fluid, used to prepare the high-quality fractional magnetorheological fluid according to any one of claims 1-5, characterized in that, Includes the following steps: S1. Composite powder preparation: The micron-sized spherical carbonyl iron powder, composite thixotropic agent, anti-wear agent and surfactant are mechanically fused under inert gas protection. Ten minutes before the end of ball milling, a small molecule surface energy modifier is introduced by atomization spraying or airflow introduction. Ball milling continues until the end of the process, so that each component is synergistically coated on the surface of carbonyl iron powder to form a core-shell structured composite powder. S2. In-situ gelation and dispersion: The composite powder obtained in step S1 is slowly added in multiple portions to a carrier liquid pre-dispersed with organic gelling agents and polyether polyol dispersants. The mixture is first sheared and mixed uniformly at 1000 r / min at 60-70℃, and then cooled to room temperature to trigger the self-assembly of organic gelling agents to form a three-dimensional gel network, thus fixing the composite powder. The cooling rate is 0.5℃ / min to 2℃ / min. S3. Vacuum degassing treatment: Vacuum degassing is performed on the mixture cooled in step S2 to obtain the magnetorheological fluid.

7. The preparation method according to claim 6, characterized in that, In step S1, the mechanical fusion process uses a high-speed energy ball mill or a mechanical fusion machine, with a processing speed of 300 r / min to 500 r / min and a processing time of 30 min to 120 min.

8. The preparation method according to claim 6, characterized in that, The composite powder obtained in step S1 is divided into three equal parts. The carrier liquid temperature is kept at 65°C. The first part of the composite powder is slowly added at a shear rate of 1000 r / min. The system is slowly cooled to 60°C at a cooling rate of about 1°C / min. The shear rate is maintained, and the second part of the composite powder is added. The system is further cooled to 55°C at a cooling rate of about 1°C / min. The shear rate is maintained, and the last part of the composite powder is added. After all the materials are added, heating is stopped, and the system is allowed to cool slowly to room temperature at a rate of about 0.5-2°C / min.

9. The preparation method according to claim 6, characterized in that, In step S3, the vacuum degassing conditions are: degassing for 20 minutes at a vacuum of -0.08 MPa.

10. According to any one of claims 6 to 9, after step S1, the obtained composite powder is passed through a 600-mesh sieve to remove large particles and agglomerates; the final product is sealed with argon gas and stored in a dry environment below 25°C.

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