A gradient dispersion method for preparing highly stable, low-agglomeration nanofluids

Abstract

This invention relates to the field of nanofluid preparation technology and discloses a gradient dispersion preparation method for highly stable, low-agglomeration nanofluids, comprising the following steps: S1, drying, sieving, and surface activation pretreatment of nanoparticles; S2, mixing the pretreated nanoparticles with a modifier; S3, sequentially adding a pre-wetting liquid, a transition dispersion liquid, and a base liquid to form a transition suspension; S4, applying a gradient composite energy field to the transition suspension for graded deagglomeration; S5, adjusting the pH and viscosity of the deagglomerated suspension and adding a polymeric stabilizer; S6, precisely filtering the stabilized nanofluid to obtain a highly stable, low-agglomeration nanofluid. By employing a full-chain gradient dispersion technology solution involving nanoparticle pretreatment, surface modification, gradient wetting pre-dispersion, gradient composite energy field deagglomeration, multi-dimensional stabilization control, and multi-stage precision filtration, the problems of easy agglomeration, incomplete dispersion, and uneven particle size distribution of nanoparticles are solved.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of nanofluid preparation, in particular to a gradient dispersion preparation method of high-stability low-aggregation nanofluid. BACKGROUND

[0002] Nanofluid is a new type of nanofunctional suspension system formed by uniformly dispersing metal, metal oxide, carbon-based, nitride and other nanoscale particles in water, oil, alcohol and other base liquids. With the unique high specific surface area, interface effect and size effect of nanomaterials, nanofluid has significant performance advantages in the fields of heat transfer enhancement, micro-channel cooling, industrial lubrication, solar heat collection, and electrochemical heat dissipation. The dispersion uniformity, particle aggregation degree and system stability of nanofluid directly determine its performance, service life and industrial application feasibility.

[0003] The current mainstream preparation method of nanofluid is still mainly the traditional two-step method, which generally uses mechanical stirring, single ultrasonic treatment or simple addition of dispersants to realize particle dispersion. This kind of method does not systematically design the particle interface, wetting process and energy field effect, and it is difficult to effectively break the high surface energy and strong aggregation trend of nanometer particles, resulting in easy aggregation of nanometer particles in liquid phase, uneven particle size distribution, incomplete dispersion, and unable to realize the real low-aggregation dispersion state, which seriously restricts the performance of nanofluid and industrial application. SUMMARY

[0004] In view of the shortcomings of the prior art, the present application provides a gradient dispersion preparation method of high-stability low-aggregation nanofluid, which solves the problems of easy aggregation of nanometer particles, incomplete dispersion and uneven particle size distribution.

[0005] To achieve the above purpose, the present application realizes the following technical scheme: a gradient dispersion preparation method of high-stability low-aggregation nanofluid, comprising the following steps: S1, drying, screening and surface activation pretreatment of nanometer particles; S2, mixing the pretreated nanometer particles with a modifier for surface modification treatment; S3, three-stage gradient wetting pre-dispersion of the modified particles, sequentially adding pre-wetting liquid, transition dispersion liquid and base liquid to form a transition suspension; S4, applying a gradient composite energy field to the transition suspension for hierarchical depolymerization; S5, adjusting the pH and viscosity of the depolymerized suspension and adding a high molecular stabilizer to realize multi-dimensional stability control; S6, precision filtering of the stabilized nanofluid to obtain high-stability low-aggregation nanofluid.

[0006] By adopting the above technical solution, the problem of nanoparticle dispersion is systematically solved from three aspects: inhibiting agglomeration, breaking agglomeration, and long-term stabilization, due to the use of full-process gradient dispersion process, composite energy field deagglomeration and multi-dimensional stabilization synergy. Therefore, the effect of uniform nanoparticle dispersion, low agglomeration rate, long-term suspension stability and industrial production is achieved.

[0007] Preferably, in step S1, the nanoparticles need to be vacuum dried at 60-120℃ to a moisture content of ≤3% in advance, and agglomerates need to be removed by 200-500 mesh sieving; surface activation is performed by plasma treatment with a power of 100-300W and a treatment time of 5-15min.

[0008] By adopting the above technical solutions, the surface energy of the particles is effectively reduced by thoroughly removing adsorbed water through vacuum drying, removing coarse agglomerates through graded sieving, and enhancing surface active sites through plasma activation. Therefore, the particles are uniform in their initial state, have a strong bond after subsequent modification, and are not prone to spontaneous agglomeration during the dispersion process.

[0009] Preferably, in step S2, the surface modification is divided into two stages of gradient stirring: The first stage involves low-speed stirring at 300–500 r / min for 10–15 min. The second stage involves high-speed stirring at a speed of 800–1000 r / min for 20–30 min. The modifier is a compound system selected from one or more of the following: silane coupling agents, surfactants, and dispersants.

[0010] By adopting the above technical solution, the wettability and compatibility of particles are significantly improved by using two-stage gradient stirring to achieve initial coating and deep bonding, constructing a double-layer interface protective layer with compound modifiers, and avoiding excessive coating by reasonable proportioning. Therefore, the effect of uniform modification, dense coating, not easy desorption, and compatibility with a variety of base liquids is obtained.

[0011] Preferably, in step S2, the modifier needs to be preheated at 40-60°C for 5-10 minutes in advance, and the modifier is preferably a compound system of silane coupling agent and nonionic dispersant or fatty acid and nonionic surfactant.

[0012] By adopting the above technical solution, the modification efficiency is higher, the dispersion effect is better, and the particle surface energy is lower. This is because the preheating reduces the viscosity of the modifier, improves the fluidity and reactivity, and the compound system has both coupling anchoring and dispersion stabilization effects, thus strengthening the interfacial bonding effect.

[0013] Preferably, in step S3, the pre-wetting liquid needs to be pre-treated at a constant temperature of 25-35℃, and the surface tension is ≤30mN / m; when the modified particles are added to the pre-wetting liquid, they are added at a uniform rate, and the addition time is controlled at 5-10min.

[0014] By adopting the above technical solution, the particles are rapidly wetted by a low surface tension pre-wetting liquid, interface fluctuations are avoided under constant temperature conditions, and local concentrations are prevented by uniform dripping, thus eliminating agglomeration in the liquid from the source. Therefore, the effect of complete particle wetting, no instantaneous agglomeration, and uniform initial dispersion is achieved.

[0015] Preferably, in step S3, the three-stage gradient wetting and pre-dispersion employs three-stage gradient stirring: The first stage involves low-speed stirring at 300–400 r / min for 5–10 min. The second stage involves medium-speed stirring at 600–800 r / min for 15–20 min. The third stage involves high-speed stirring at 900–1100 rpm for 25–35 minutes.

[0016] By adopting the above technical solution, the dispersion intensity is gradually increased by three-stage gradient stirring, and the interfacial energy difference is gradually eliminated by the gradient liquid system, so as to achieve a smooth transition dispersion. Therefore, the dispersion is more complete, the system is more stable, and there are no dead corners of local agglomeration.

[0017] Preferably, in S4, the depolymerization of the composite energy field is divided into gradient treatment, with energy increasing from low to high. First, mechanical shearing is performed at 3000-10000 r / min for 10-20 min, then ultrasonic cavitation is performed intermittently at 200-800 W for 20-40 min, and finally high-pressure micro-jets at 80-150 MPa are cyclically repeated 2-5 times.

[0018] By adopting the above technical solution, soft agglomerates, medium agglomerates, and hard agglomerates are broken down step by step by using low, medium, and high gradient energy fields, and intermittent processing avoids local overheating, thus restoring the low-agglomeration dispersion state to the greatest extent. Therefore, the effect of completely breaking down agglomerates, narrowing the particle size distribution, and greatly improving the dispersion uniformity is achieved.

[0019] Preferably, in step S5, for the water-based system, the pH is adjusted so that the absolute value of the particle zeta potential is ≥30mV; the amount of polymeric stabilizer added is 0.1-1wt%, and the viscosity of the system is adjusted to 1-10mPa·s.

[0020] By adopting the above technical solution, the suspension stability is comprehensively improved by the synergistic effect of strong electrostatic repulsion, high molecular steric hindrance, and moderate viscosity sedimentation suppression mechanism. Therefore, the effect of long-term static storage without sedimentation, stratification, aggregation, and a significantly extended storage life is achieved.

[0021] Preferably, in step S5, the temperature is controlled to be ≤30℃ throughout the stabilization process, and a closed, light-proof stirring method is used, with a stirring speed of 400-600 r / min and a stirring time of 10-15 min.

[0022] By adopting the above technical solutions, the system deteriorates and agglomerates due to low temperature and light protection, and the stabilizer is evenly dispersed by gentle stirring, thus maintaining the stability of the system. Therefore, the system achieves more complete stabilization, no more particle aggregation, and higher consistency in the performance of the finished product.

[0023] Preferably, in step S6, the fine filtration adopts multi-stage filtration, with the first stage filtration accuracy being 5-10μm, the second stage filtration accuracy being 0.2-1μm, and the filtration pressure being controlled at 0.1-0.3MPa.

[0024] By adopting the above technical solution, large particles and impurities are removed step by step through two-stage filtration, and the pressure can be controlled to avoid filter membrane clogging and particle re-agglomeration, thus ensuring the purity of the finished product. Therefore, the nanofluid is free of impurities and large particles, does not clog during long-term use, and has further improved stability.

[0025] This invention provides a gradient dispersion method for preparing highly stable, low-agglomeration nanofluids. It offers the following advantages: 1. This invention employs a full-chain gradient dispersion technology solution, which includes nanoparticle pretreatment, surface modification, gradient wetting pre-dispersion, gradient composite energy field deagglomeration, multi-dimensional stabilization control, and multi-stage precision filtration. This solution achieves the technical effect of suppressing agglomeration at the source, breaking down hard agglomerates step by step, and realizing highly monodisperse nanoparticles. Compared with existing technologies that rely on single stirring, single ultrasound, or simple blending, this invention solves the problems of easy agglomeration, incomplete dispersion, and uneven particle size distribution of nanoparticles.

[0026] 2. This invention employs gradient wetting to reduce the interfacial energy barrier, compound modification to construct an interfacial protective layer, and multi-dimensional stability to achieve synergistic effects of electrostatics, steric hindrance, and viscosity. This achieves the technical effect of long-term suspension stability of nanofluids, making them less prone to sedimentation and stratification. Compared with existing technologies that rely on a single dispersant or short-term dispersion, this invention solves the problems of poor stability, short storage period, and easy rapid sedimentation.

[0027] 3. The present invention adopts an integrated technical solution with controllable process parameters, smooth step connection, adaptability to various particles and base liquids, and scale-up production. It achieves the technical effects of good batch repeatability, wide applicability, and continuous industrial preparation. Compared with the existing technical solutions with complex processes, harsh conditions, and only applicable to small-batch preparation in the laboratory, it solves the problems of difficulty in scaling up, high cost, and poor versatility. Attached Figure Description

[0028] Figure 1 This is a schematic diagram of the method steps of the present invention. Detailed Implementation

[0029] The technical solution of the present invention will now be clearly and completely described with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0030] Please see the appendix Figure 1 This invention provides a gradient dispersion preparation method for highly stable, low-agglomeration nanofluids, comprising the following steps: S1, the nanoparticles are dried, sieved and surface activated pretreatment; Furthermore, in S1, the nanoparticles need to be vacuum dried at 60-120℃ to a moisture content of ≤3% in advance, and agglomerates need to be removed by 200-500 mesh sieve; surface activation is performed by plasma treatment with a power of 100-300W and a treatment time of 5-15min. Specifically, vacuum drying can completely remove adsorbed water and volatile impurities from the particle surface, avoiding uneven coating caused by moisture interference during subsequent modification; sieving removes coarse agglomerates, ensuring uniform initial particle size; plasma activation can significantly increase the number of active sites on the particle surface and reduce surface energy, providing a basis for efficient binding of the modifier and particle surface in step S2, while reducing the tendency of spontaneous agglomeration during subsequent dispersion.

[0031] S2, the pretreated nanoparticles are mixed with a modifier and then subjected to surface modification treatment; Furthermore, in S2, the surface modification is divided into two stages of gradient stirring: The first stage involves low-speed stirring at 300–500 r / min for 10–15 min. The second stage involves high-speed stirring at a speed of 800–1000 r / min for 20–30 min. The modifier is a compound system selected from one or more of silane coupling agents, surfactants, and dispersants; In S2, the modifier needs to be preheated at 40-60℃ for 5-10 minutes in advance. The preferred modifier is a compound system of silane coupling agent and nonionic dispersant or fatty acid and nonionic surfactant. Specifically, preheating the modifier can reduce its viscosity, improve its fluidity and reactivity. Two-stage gradient stirring can first make the modifier uniformly coat the particles, and then strengthen the chemical bonding and physical adsorption to form a dense and stable interfacial protective layer. After S1 activation and S2 modification, the surface wettability of the particles is significantly improved, and they can smoothly enter the gradient wetting pre-dispersion system of S3 step, avoiding instantaneous agglomeration when directly added to the base liquid.

[0032] S3, the modified particles are pre-dispersed by three-stage gradient wetting, and pre-wetting liquid, transition dispersion liquid and base liquid are added in sequence to form a transition suspension; Furthermore, in S3, the pre-wetting liquid needs to be pre-treated at a constant temperature of 25-35℃, and the surface tension should be ≤30mN / m; when the modified particles are added to the pre-wetting liquid, they should be added at a uniform rate, and the addition time should be controlled at 5-10min. In S3, the three-stage gradient wetting and pre-dispersion method employs three-stage gradient stirring: The first stage involves low-speed stirring at 300–400 r / min for 5–10 min. The second stage involves medium-speed stirring at 600–800 r / min for 15–20 min. The third stage involves high-speed mixing at 900–1100 r / min for 25–35 min. Specifically, the constant-temperature, low-surface-tension pre-wetting liquid can quickly wet the particle surface, and the uniform droplet addition avoids local high concentration and agglomeration; the three-stage gradient stirring gradually improves the dispersion intensity, and the gradient liquid system gradually eliminates the interfacial energy difference, so that the particles smoothly transition from complete wetting to uniform dispersion, forming a non-agglomerated transition suspension, providing a uniform and stable material basis for the efficient deagglomeration of the composite energy field in step S4.

[0033] S4, apply a gradient composite energy field to the transition suspension to perform graded depolymerization; Furthermore, in S4, the depolymerization of the composite energy field is divided into gradient treatment, with energy increasing from low to high. First, mechanical shearing is performed at 3000-10000 r / min for 10-20 min, then ultrasonic cavitation is performed intermittently at 200-800 W for 20-40 min, and finally high-pressure micro-jets are circulated at 80-150 MPa for 2-5 times. Specifically, the gradient recombination energy field acts step by step from low to high, which can first break up soft agglomerates, then break up medium agglomerates, and finally break up hard agglomerates that are difficult to handle, so as to restore the low-agglomeration dispersion state of nanoparticles to the greatest extent. Intermittent ultrasound and circulating microjets can avoid local overheating that leads to secondary agglomeration of particles. The suspension after S4 deagglomeration has a narrower particle size distribution and more uniform dispersion, and can directly enter the S5 step for stabilization and control.

[0034] S5 adjusts the pH and viscosity of the depolymerized suspension and adds a polymer stabilizer to achieve multi-dimensional stabilization control. Furthermore, in S5, for water-based systems, the pH is adjusted so that the absolute value of the particle zeta potential is ≥30mV; the amount of polymeric stabilizer added is 0.1-1wt%, and the system viscosity is adjusted to 1-10mPa·s; In S5, the temperature is controlled at ≤30℃ throughout the stabilization process, and a closed, light-proof stirring method is used with a stirring speed of 400-600 r / min and a stirring time of 10-15 min. Specifically, the regulation of potential creates strong electrostatic repulsion, which, combined with the steric hindrance of polymers and appropriate viscosity to inhibit sedimentation, achieves long-term stability through a triple mechanism. Low temperature, airtight and light-proof design prevents system deterioration and avoids particle re-aggregation. The suspension stability of the nanofluid after S5 stabilization treatment is greatly improved, meeting the requirements of precision filtration and long-term storage in the S6 step.

[0035] S6, the stabilized nanofluid is precisely filtered to obtain a highly stable, low-agglomeration nanofluid; Furthermore, in S6, the fine filtration adopts multi-stage filtration, with the first stage filtration accuracy of 5-10μm, the second stage filtration accuracy of 0.2-1μm, and the filtration pressure controlled at 0.1-0.3MPa; Specifically, the two-stage precision filtration can remove undispersed large particles, impurities and residual agglomerates step by step, and control the filtration pressure to avoid filter membrane clogging and particle re-agglomeration under pressure; the final nanofluid has uniform particle size, no obvious agglomeration, and does not settle after long-term standing, and has both high stability and low agglomeration characteristics, and can be directly used in scenarios such as enhanced heat transfer, cooling and lubrication.

[0036] The following is a further description with reference to the embodiments: Example 1: A gradient dispersion preparation method for a highly stable, low-agglomeration nanofluid, comprising the following steps: S1, Nanoparticle Pretreatment: Take 100g of 30nm alumina nanoparticles and dry them in an 80℃ vacuum drying oven for 4h until the moisture content is ≤3%; remove large particle agglomerates by 300-mesh sieve; use 200W plasma surface activation treatment for 10min to enhance the active sites on the particle surface and reduce the surface energy, providing a good interface basis for subsequent modification and dispersion.

[0037] S2, Surface modification treatment: The pretreated alumina particles are mixed with silane coupling agent KH-550 and nonionic dispersant OP-10 at a mass ratio of 1:0.03:0.02; the modifier is preheated at 50℃ for 8 minutes to reduce viscosity and improve dispersion activity. Two-stage gradient stirring is performed: the first stage is low-speed stirring at 400 r / min for 12 min, which allows the modifier to initially and uniformly coat the particles; the second stage is high-speed stirring at 900 r / min for 25 min, which strengthens the chemical bonding and physical adsorption between the modifier and the particle surface, forming a dense interfacial protective layer; after modification, the wettability of the particles is significantly improved, and they can smoothly enter the subsequent gradient wetting and dispersion process.

[0038] S3, three-stage gradient wetting and pre-dispersion: the pre-wetting solution is ethanol, which has been pre-treated at 30℃ and has a surface tension ≤30mN / m; the modified particles are added to the ethanol at a uniform rate, and the addition time is controlled at 8min. A three-stage gradient stirring method was adopted: the first stage was low-speed stirring at 350 r / min for 8 min to achieve initial complete wetting of particles; the second stage was medium-speed stirring at 700 r / min for 18 min to complete the transition dispersion matching; the third stage was high-speed stirring at 1000 r / min for 30 min to gradually eliminate the interfacial energy difference and form a uniform, non-agglomerated transition suspension, providing a stable material system for subsequent deagglomeration in the composite energy field.

[0039] S4, graded deagglomeration using gradient composite energy field: The transition suspension is treated with a gradient composite energy field from low to high: first, mechanical shearing at 6000 r / min for 15 min is used to break up soft agglomerates; then, intermittent ultrasonic cavitation at 500 W is used for 30 min to break up medium agglomerates; finally, high-pressure micro-jet at 100 MPa is used for 3 cycles to break up residual hard agglomerates. Throughout the process, local overheating that could lead to secondary agglomeration is avoided, so that the particles reach a low-agglomeration dispersion state.

[0040] S5, multi-dimensional stabilization control: Sodium hydroxide is used to adjust the pH of the system so that the absolute value of the particle zeta potential is ≥30mV, forming strong electrostatic repulsion; 0.5wt% polyvinylpyrrolidone (PVP) is added as a polymeric stabilizer to adjust the viscosity of the system to 3mPa·s; the temperature is controlled at ≤30℃ throughout the process, and the system is sealed and protected from light, and stirred at 500r / min for 12min. Through the triple synergistic effect of electrostatic repulsion, steric hindrance, and viscosity inhibition, long-term suspension stability is enhanced.

[0041] S6, multi-stage precision filtration: adopts two-stage precision filtration. The first stage has a filtration precision of 8μm to remove coarse impurities; the second stage has a filtration precision of 0.5μm to remove residual undispersed large particles; the filtration pressure is controlled at 0.2MPa to avoid particle re-agglomeration under pressure, and finally obtains a highly stable, low-agglomeration alumina water-based nanofluid with a mass fraction of about 5%.

[0042] Example 2: A gradient dispersion preparation method for a highly stable, low-agglomeration nanofluid, comprising the following steps: S1, Nanoparticle pretreatment: Take 80g of 50nm copper oxide nanoparticles, vacuum dry at 100℃ for 3h, with a moisture content ≤2.5%; sieve through 400 mesh; activate with 250W plasma for 8min to remove surface impurities and enhance surface activity.

[0043] S2, Surface modification treatment: Oleic acid and Span80 compound modifier are used, preheated at 55℃ for 7 minutes; and mixed with copper oxide particles at a mass ratio of 1:0.07. The first stage involves low-speed stirring at 400 rpm for 10 minutes; the second stage involves high-speed stirring at 900 rpm for 25 minutes. This process forms a hydrophobic and oleophilic protective layer on the particle surface, making it compatible with oil-based systems and significantly reducing the tendency of oil phase agglomeration.

[0044] S3, three-stage gradient wetting pre-dispersion: the pre-wetting solution is isopropanol, constant temperature 30℃; particles are added dropwise at a uniform rate for 8 min; Three-stage stirring: stirring at low speed (350 r / min) for 8 minutes, at medium speed (700 r / min) for 18 minutes, and at high speed (1000 r / min) for 30 minutes; gradually transitioning to mineral oil base liquid to eliminate interfacial tension differences and form a uniform transition suspension.

[0045] S4, graded depolymerization in a gradient composite energy field: shearing at 8000 r / min for 12 min, intermittent ultrasonication at 600 W for 25 min, and microfluidic circulation at 120 MPa twice; gradually breaking down agglomerates to obtain a highly uniform oil-based suspension.

[0046] S5, multi-dimensional stabilization control: adjust the system viscosity to 5 mPa·s, add 0.6 wt% polyisobutylene stabilizer; seal and protect from light, ≤30℃, stir at 500 r / min for 12 min to enhance the long-term stability of the oil phase.

[0047] S6, multi-stage precision filtration: first stage 6μm filtration, second stage 0.5μm filtration, pressure 0.2MPa, to obtain copper oxide oil-based nanofluid with a mass fraction of 3%.

[0048] Example 3: A gradient dispersion preparation method for a highly stable, low-agglomeration nanofluid, comprising the following steps: S1, Nanoparticle pretreatment: 90g of 25nm titanium dioxide particles, vacuum dried at 90℃ for 3.5h, moisture content ≤2.5%; sieved through 350 mesh; activated by 220W plasma for 9min.

[0049] S2, Surface modification treatment: Silane coupling agent KH-560 is compounded with anionic dispersant and preheated at 50℃ for 8 min; two-stage gradient stirring: 400 r / min for 12 min, and 900 r / min for 25 min.

[0050] S3, three-stage gradient wetting and pre-dispersion: pre-wetting with ethanol, adding dropwise at a uniform rate for 7 min; three-stage stirring: stirring at 350 r / min for 8 min, stirring at 700 r / min for 18 min, stirring at 1000 r / min for 30 min, smoothly transitioning to the water-based system.

[0051] S4, graded depolymerization in gradient composite energy field: shearing at 5500 r / min for 18 min, sonication at 450 W for 30 min, and microfluidization at 100 MPa for 3 times.

[0052] S5, multi-dimensional stabilization control: pH adjusted to 9.0, absolute value of Zeta potential ≥35mV, 0.4wt% PVA added, viscosity adjusted to 2.5mPa·s; low temperature closed stirring for 12min.

[0053] S6, multi-stage precision filtration: first stage 8μm, second stage 0.5μm, filtration pressure 0.2MPa, yielding 4wt% titanium dioxide nanofluid.

[0054] Example 4 differs from Example 1 in that step S4 uses a lower energy range composite energy field: mechanical shear 3000 r / min, ultrasonic power 200 W, microjets pressure 80 MPa, and the remaining process parameters are the same as in Example 1.

[0055] Example 5 differs from Example 1 in that isopropanol is used as the pre-wetting liquid in step S3, and the stirring speed of the three stages is reduced by 100 r / min. All other process parameters are the same as in Example 1.

[0056] Example 6 differs from Example 1 in that, in step S5, the viscosity of the system is adjusted to 10 mPa·s, the amount of polymer stabilizer added is increased to 1 wt%, and the remaining process parameters are the same as in Example 1.

[0057] Example 7 differs from Example 1 in that step S6 employs a 0.2μm high-precision two-stage filtration to further remove trace agglomerates; all other process parameters remain the same as in Example 1. Comparative Example 1 differs from Example 1 in that the mass ratio of nanoparticles to modifier in step S2 is 1:0.5, instead of the 1:0.01–1:0.15 compounding ratio specified in this invention. All other process parameters are consistent with Example 1. The resulting nanofluid exhibits severe agglomeration and obvious stratification and sedimentation after standing for 7 days.

[0058] Comparative Example 2 uses the same alumina nanoparticles as in Example 1, without the surface modification treatment in step S2, and directly performs gradient wetting, energy field deagglomeration and stabilization control, with the remaining steps being the same; the test results show that the absolute value of the particle zeta potential is only 12mV, a large amount of particles settle after standing for 3 days, the particle size distribution is extremely uneven, and the dispersion stability is extremely poor.

[0059] Comparative Example 3 differs from Example 1 in that step S3, three-level gradient wetting and pre-dispersion, is omitted, and the modified particles are directly added to deionized water for dispersion, while the rest of the process is the same; the resulting nanofluid has poor initial dispersibility, contains a large number of agglomerates, and shows obvious precipitation after standing for 10 days, with a significant decrease in long-term stability.

[0060] Comparative Example 4 differs from Example 1 in that step S4 only uses single mechanical shearing and does not perform composite energy field gradient deagglomeration, while the rest of the process is the same; a large number of hard agglomerates still remain in the system, the particle size uniformity is poor, and significant sedimentation occurs after standing for 15 days, resulting in a significant reduction in dispersion effect.

[0061] Comparative Example 5 differs from Example 1 in that step S5 does not involve pH adjustment or Zeta potential regulation; only a polymeric stabilizer is added, while the rest of the process remains the same. The electrostatic repulsion between particles is weak, making them prone to aggregation. After standing for 20 days, they exhibit stratification and lack long-term suspension stability.

[0062] The following examples, using experimental cases, further illustrate the performance differences between Examples 2-7 and Comparative Examples 1-5 and Example 1: In Experiment 1, the average particle size and agglomerate ratio were determined using GB / T29022-2021 "Dynamic Light Scattering Method (DLS) for Particle Size Analysis". The average particle size and agglomerate ratio of the nanofluid were determined using a dynamic light scattering particle size analyzer. Samples of finished nanofluids prepared in the examples and comparative examples were selected, and samples with obvious stratification, sedimentation, or agglomeration were removed. First, take an appropriate amount of nanofluid and dilute it with the corresponding basic dispersion to a suitable test concentration. Set the test temperature to 25℃ and the equilibration time to 60s. Repeat the test 3 times for each group of samples, and take the average value after removing the maximum and minimum values. The agglomerate ratio is calculated as the volume fraction of particles with a particle size >100nm. During the test, maintain the ambient temperature at 25±2℃. Before the test, the sample is equilibrated in this environment for 12h.

[0063] Experiment 2: Zeta potential detection. The zeta potential of the nanofluid was detected according to GB / T32671.2-2019 "Methods for measuring zeta potential of colloidal systems - Part 2: Optical method" using a laser Doppler electrophoresis zeta potential meter. The uniform nanofluid samples prepared in the examples and comparative examples were filtered through a 0.22 μm filter membrane to remove impurities. The test temperature was set at 25℃ and the electrophoresis voltage at 150V. Each group of samples was tested 5 times, and the absolute average value was taken after removing the maximum and minimum values. During the test, the ambient temperature was kept at 25±2℃, and the samples were equilibrated in this environment for 12 hours before the test.

[0064] Experiment 3: Static sedimentation rate test. GB / T38431-2019 "Stability Evaluation of Particulate Dispersion Systems - Static Multiple Light Scattering Method" was used to test the sedimentation rate of the nanofluid after 30 days and 60 days of static standing. A stoppered graduated cylinder was used. The finished nanofluids prepared in the examples and comparative examples were selected, and the same volume of the test liquid was placed in the graduated cylinder. The settling temperature was 25±2℃. The height of the upper clear liquid and the total liquid height were measured after 30 days and 60 days of settling. The sedimentation rate was calculated according to the formula: sedimentation rate (%) = height of upper clear liquid / total liquid height × 100%. Three parallel tests were conducted for each group of samples. The maximum and minimum values ​​were removed and the average value was taken. The samples were equilibrated for 24 hours under the test environment before the test.

[0065] Table 1. Comparison of Nanofluid Performance Test Results

[0066] Based on the differences between Examples 1-7 and Comparative Examples 1-5 and the performance test data table, it can be seen that the synergistic process of nanoparticle pretreatment, surface modification, three-level gradient wetting pre-dispersion, gradient composite energy field deagglomeration, multi-dimensional stabilization control, and multi-level precision filtration in this invention has a significant impact on the average particle size, agglomerate ratio, Zeta potential, sedimentation rate after 30 days of standing, and sedimentation rate after 60 days of standing. Moreover, each process step has a good effect on sufficient wetting, uniform dispersion, thorough deagglomeration, stable and durable performance, and resistance to agglomeration, thus achieving the dual goals of low agglomeration, high stability, and industrialization of nanofluids.

[0067] In Comparative Example 1, the mass ratio of nanoparticles to modifier in step S2 exceeded the limits of this invention. The excessive amount of modifier led to over-coating between particles and easy bridging and agglomeration. As a result, the average particle size of the obtained nanofluid increased significantly, the proportion of agglomerates rose to 12.7%, the absolute value of the Zeta potential was only 18.6 mV, the sedimentation rate after 30 days of standing was 18.3%, and the sedimentation rate after 60 days of standing was as high as 42.7%. The dispersion uniformity and long-term stability decreased significantly, which could not meet the requirements for the use of highly stable nanofluids. Comparative Example 2 used the same alumina nanoparticles as Example 1, but without the surface modification treatment in step S2. The particles had high surface energy, poor wettability, and lacked an interfacial protective layer. Directly carrying out the subsequent dispersion process resulted in severe agglomeration of the system, with an average particle size of 92.3 nm, an agglomerate ratio of 24.6%, and an absolute value of only 11.8 mV for the Zeta potential. A large amount of sedimentation occurred after standing for 3 days, and the sedimentation rate was close to 69% after standing for 60 days. The dispersion stability was extremely poor, and it completely lost its practical value. Comparative Example 3 omits step S3, three-stage gradient wetting and pre-dispersion, and directly adds the modified particles to the base liquid for dispersion. The interfacial energy barrier is high and the local concentration is too high at the moment the particles enter the liquid, forming a large number of initial agglomerates that are difficult to be broken by the subsequent energy field. The agglomerates account for 18.2%, the sedimentation rate is 24.6% after standing for 30 days, and the sedimentation rate exceeds 51% after standing for 60 days. The initial dispersion is poor and it is easy to stratify and precipitate during long-term storage. In Comparative Example 4, step S4 only uses single mechanical shearing without gradient composite energy field deagglomeration, which cannot effectively break up hard agglomerates. A large number of agglomerated particles remain in the system, with poor particle size uniformity. The agglomerates account for 9.8%, and the sedimentation rate reaches 28.5% after standing for 60 days. The dispersion effect and stability are significantly worse than the technical solution of this invention. In Comparative Example 5, step S5 did not involve pH adjustment or Zeta potential regulation. It relied solely on the steric hindrance provided by the polymeric stabilizer, resulting in insufficient electrostatic repulsion between particles. This led to slow aggregation, with a sedimentation rate of 9.7% after 30 days of standing and rising to 22.4% after 60 days. The long-term suspension stability was insufficient, making it difficult to meet the requirements for long-term storage and industrial applications.

[0068] The finished nanofluid prepared in the examples exhibits excellent core performance indicators, fully meeting the preset performance requirements: average particle size 30–50 nm, agglomerate ratio ≤3%, absolute value of Zeta potential ≥30 mV, sedimentation rate ≤2.5% after 30 days of standing, and sedimentation rate ≤5% after 60 days of standing. At the same time, it achieves low agglomeration dispersion and long-term stability of nanoparticles. The system has no obvious stratification, no agglomeration, and no large particle agglomeration. It has excellent comprehensive performance and can effectively improve the reliability and lifespan of nanofluids in scenarios such as enhanced heat transfer, cooling, lubrication, and solar thermal collection.

[0069] Among them, Examples 4, 5, and 7, due to process parameters being at the boundary of the set range or adapted to special particle systems, have slightly inferior performance compared to Example 1, but still maintain good overall advantages. Example 4 adopts a low parameter range configuration, which is suitable for low-concentration, low-cost, and general-purpose nanofluid scenarios, further reducing energy consumption and raw material consumption while ensuring stability. Example 6 is designed for high-concentration and high-dispersion systems, which further reduces the risk of agglomeration by increasing the energy field strength, stabilizer dosage, and filtration accuracy, and is suitable for high-performance thermal conductivity, wear resistance, special lubrication, and other scenarios with stringent stability requirements. Example 7 is adapted to carbon-based nanomaterials, solving the industry pain point of graphene's easy stacking and difficulty in dispersion, while maintaining high electrical and thermal conductivity and low agglomeration characteristics.

[0070] Example 1 achieves the optimal balance of performance, cost, and industrialization, with the strongest adaptability of process parameters: thorough pretreatment of nanoparticles, sufficient surface modification, stable gradient wetting, efficient deagglomeration in the composite energy field, precise stabilization control, and reasonable precision filtration. The prepared nanofluid has performance that is superior to the preset standard in all aspects. Moreover, the preparation process is controllable, has good batch repeatability, does not require extreme equipment, and is easy to achieve large-scale continuous production. Its cost-effectiveness advantage is significant, with a sedimentation rate reduced by more than 80% and a stable storage time extended by more than 3 times compared to the traditional two-step method. Compared to the single dispersion process, the number of agglomerates is reduced by more than 70%. It can be widely adapted to various systems such as water-based, oil-based, and alcohol-based systems, covering a variety of application scenarios such as enhanced heat transfer, microchannel cooling, industrial lubrication, solar thermal collection, and electrochemical heat dissipation.

[0071] The core processes in Examples 1-7 exhibit a deep synergistic effect: pretreatment and surface modification work together to remove impurities and enhance interfacial activity, laying the foundation for uniform dispersion; surface modification and gradient wetting work together to reduce interfacial energy difference and suppress instantaneous agglomeration at the source; gradient wetting and composite energy field deagglomeration work together to break down soft agglomerates into hard agglomerates step by step, achieving a low-agglomeration dispersion state; composite energy field deagglomeration and multi-dimensional stabilization work together, combining the triple effects of electrostatic repulsion, steric hindrance, and viscosity inhibition to ensure long-term suspension stability; stabilization regulation and multi-stage precision filtration work together to remove residual large particles, further improving the uniformity and reliability of the system; each process has mild conditions, low reagent dosage, and strong process closed-loop characteristics, which aligns with the concept of green, efficient, low-cost, and large-scale production.

[0072] Example 1 optimizes key parameters such as vacuum drying temperature of 80℃, plasma activation of 200W, modifier compounding ratio, three-stage gradient stirring, gradient composite energy field, Zeta potential ≥30mV, and two-stage precision filtration to achieve seamless connection of each process step, maximize the synergistic advantages, and fully demonstrate the scientific nature, rationality, and irreplaceability of the process steps and parameter range of the present invention.

[0073] Comparative Examples 1-5 show that the overall synergistic chain broke due to the absence of a single process step or the loss of parameter control: Comparative Example 1 damaged the rationality of the modified ratio, Comparative Example 2 lacked interface protection, Comparative Example 3 damaged the gradient dispersion core, Comparative Example 4 lost its efficient deagglomeration ability, and Comparative Example 5 weakened the stabilization mechanism. All of these examples demonstrate the necessity and advancement of the whole-chain gradient dispersion + multi-dimensional stabilization technology solution of this invention, and further illustrate that the synergistic effect of each process step is the core guarantee for achieving low agglomeration, high stability and industrialization of nanofluids.

[0074] In summary, this invention, through the core technology design of nanoparticle pretreatment, surface modification, three-level gradient wetting pre-dispersion, gradient composite energy field deagglomeration, multi-dimensional stabilization control, and multi-level precision filtration, combined with the synergistic optimization of various process parameters, effectively solves the technical problems of severe agglomeration, poor stability, rapid sedimentation, low batch repeatability, and difficulty in industrialization in existing nanofluid preparation processes. It significantly improves the dispersion uniformity, long-term stability, and performance of the finished nanofluid, realizing low-cost, high-efficiency, and large-scale preparation of nanofluids. At the same time, the process is simple, the conditions are mild, and the raw materials are widely adaptable, which is in line with the industrial development concept of high-performance functional fluids and has important application value and broad market prospects.

[0075] Although embodiments of the invention have been shown and described, it will be understood by those skilled in the art that various changes, modifications, substitutions and alterations can be made to these embodiments without departing from the principles and spirit of the invention, the scope of which is defined by the appended claims and their equivalents.

Claims

1. A gradient dispersion preparation method for highly stable, low-agglomeration nanofluids, characterized in that, Includes the following steps: S1, the nanoparticles are dried, sieved and surface activated pretreatment; S2, the pretreated nanoparticles are mixed with a modifier and then subjected to surface modification treatment; S3, the modified particles are pre-dispersed by three-stage gradient wetting, and pre-wetting liquid, transition dispersion liquid and base liquid are added in sequence to form a transition suspension; S4, apply a gradient composite energy field to the transition suspension to perform graded depolymerization; S5 involves adjusting the pH and viscosity of the depolymerized suspension and adding a polymeric stabilizer. S6 involves precise filtration of the stabilized nanofluid to obtain a highly stable, low-agglomeration nanofluid.

2. The gradient dispersion preparation method for a highly stable, low-agglomeration nanofluid according to claim 1, characterized in that, In step S1, the nanoparticles need to be vacuum dried at 60-120℃ to a moisture content of ≤3% in advance, and agglomerates need to be removed by 200-500 mesh sieve; the surface activation is carried out by plasma treatment with a power of 100-300W and a treatment time of 5-15min.

3. The gradient dispersion preparation method for a highly stable, low-agglomeration nanofluid according to claim 1, characterized in that, In step S2, the surface modification is divided into two stages of gradient stirring: The first stage involves low-speed stirring at 300–500 r / min for 10–15 min. The second stage involves high-speed stirring at a speed of 800–1000 r / min for 20–30 min. The modifier is a compound system selected from one or more of the following: silane coupling agents, surfactants, and dispersants.

4. The gradient dispersion preparation method for a highly stable, low-agglomeration nanofluid according to claim 1, characterized in that, In S2, the modifier needs to be preheated at 40-60℃ for 5-10 minutes in advance. The modifier is preferably a compound system of silane coupling agent and nonionic dispersant or fatty acid and nonionic surfactant.

5. The gradient dispersion preparation method for a highly stable, low-agglomeration nanofluid according to claim 1, characterized in that, In step S3, the pre-wetting liquid needs to be pre-treated at a constant temperature of 25-35℃, and the surface tension should be ≤30mN / m. When the modified particles are added to the pre-wetting liquid, they are added at a uniform rate, and the addition time is controlled at 5-10min.

6. The gradient dispersion preparation method for a highly stable, low-agglomeration nanofluid according to claim 1, characterized in that, In step S3, the three-stage gradient wetting and pre-dispersion employs three-stage gradient stirring: The first stage involves low-speed stirring at 300–400 r / min for 5–10 min. The second stage involves medium-speed stirring at 600–800 r / min for 15–20 min. The third stage involves high-speed stirring at 900–1100 rpm for 25–35 minutes.

7. The gradient dispersion preparation method for a highly stable, low-agglomeration nanofluid according to claim 1, characterized in that, In S4, the depolymerization of the composite energy field is divided into gradient treatment, which is carried out in order of energy from low to high. First, mechanical shearing is performed at 3000-10000 r / min for 10-20 min, then ultrasonic cavitation is performed intermittently at 200-800 W for 20-40 min, and finally high-pressure micro-jets at 80-150 MPa are cyclically repeated 2-5 times.

8. The gradient dispersion preparation method for a highly stable, low-agglomeration nanofluid according to claim 1, characterized in that, In S5, for the water-based system, the pH is adjusted so that the absolute value of the particle zeta potential is ≥30mV; the amount of polymeric stabilizer added is 0.1-1wt%, and the viscosity of the system is adjusted to 1-10mPa·s.

9. The gradient dispersion preparation method for a highly stable, low-agglomeration nanofluid according to claim 1, characterized in that, In S5, the temperature is controlled at ≤30℃ throughout the stabilization process, and a closed, light-proof stirring method is used with a stirring speed of 400-600 r / min and a stirring time of 10-15 min.

10. The gradient dispersion preparation method for a highly stable, low-agglomeration nanofluid according to claim 1, characterized in that, In S6, the fine filtration adopts multi-stage filtration, with the first stage filtration accuracy of 5-10μm, the second stage filtration accuracy of 0.2-1μm, and the filtration pressure controlled at 0.1-0.3MPa.

Images