High-stable, anti-sagging liquid-cooled composite nanofluid and preparation method thereof

Abstract

This application relates to the field of liquid cooling technology, and discloses a highly stable, anti-sagging liquid-cooled composite nanofluid and its preparation method. The composite nanofluid comprises: deionized water and 1,2-propanediol as the continuous phase, graphene and single-walled carbon nanotube composite particles as the dispersed phase, and introduces a ternary rheological control system composed of a rheology modifier, polyvinylpyrrolidone, and a polymeric dispersant in a specific ratio, endowing the fluid with thixotropic and anti-sagging properties. This application improves the overall service stability and thermal management reliability of the liquid-cooled composite nanofluid under alternating high-speed pumping and static shutdown conditions.

Description

Technical Field

[0001] This application relates to the field of liquid cooling technology, and in particular to a highly stable, anti-sagging liquid-cooled composite nanofluid and its preparation method. Background Technology

[0002] With the rapid expansion of artificial intelligence computing infrastructure, the power density of high-performance computing servers and data centers continues to break through the physical limits of traditional air cooling. Liquid cooling technology, due to its excellent heat transfer efficiency, has become a core solution in the field of thermal management for high heat flux density electronic devices. In the research field of liquid cooling media, introducing carbon nanomaterials such as graphene and single-walled carbon nanotubes into water-alcohol based liquids to prepare composite nanofluids is an important technical path to improve the thermal conductivity of cooling media. Existing technologies typically use a single dispersant such as polyvinylpyrrolidone (PVP) to disperse the aforementioned carbon nanomaterials, or use a single thickener to thicken and modify the nanofluids in order to achieve uniform dispersion of carbon nanoparticles in the base liquid.

[0003] However, the aforementioned existing technical solutions face fundamental defects in practical engineering applications: although a single dispersant system can maintain the initial dispersion of carbon nanoparticles in the short term, due to the lack of a macroscopic three-dimensional support structure, the particles inevitably agglomerate and settle under long-term static conditions driven by strong van der Waals forces, leading to a decrease in fluid thermal conductivity and the risk of pipeline blockage; while a single thickener system can increase static viscosity to delay sedimentation, its viscosity structure recovers extremely slowly after being damaged by the high shear force generated by the high-speed pumping of the liquid cooling system, and it cannot rebuild effective support for the particles in a short time after the system is shut down, and the problem of particle sedimentation and stratification remains prominent; in addition, although increasing the concentration of carbon nanoparticles can enhance the thermal conductivity, it will simultaneously lead to viscosity distortion and agglomeration, while reducing the concentration improves fluidity but loses the core thermal conductivity gain. Existing technologies have always been unable to overcome the inherent contradiction between high thermal conductivity and long-term dispersion stability.

[0004] The root cause of the aforementioned shortcomings lies in the fact that existing technologies all employ a single functional component to address the multi-dimensional dispersion stability requirements. However, the engineering stabilization of carbon nanofluids actually involves three interrelated but mechanistically distinct levels: the construction and reversible recovery of the macroscopic thixotropic network, the interfacial anchoring and steric hindrance protection of the carbon nanoparticle surface, and the cross-scale synergistic fixation between particles and the network framework. While a single component achieves the function of one level, it inevitably restricts the realization of another level. This determines that within a single-component or simple two-component framework, it is impossible to simultaneously satisfy the three interdependent engineering requirements of low viscosity under high shear (ensuring pumping efficiency), high viscosity and rapid recovery under low shear (ensuring anti-sedimentation during static placement), and long-term dispersion stability at extremely low particle concentrations (ensuring a balance between thermal conductivity and flowability). Therefore, a systematic solution from the perspective of multi-component synergistic regulation is urgently needed. Summary of the Invention

[0005] This application provides a highly stable, anti-sagging liquid-cooled composite nanofluid and its preparation method, which solves the core problems of existing carbon-based nanofluids, which cannot simultaneously achieve macroscopic thixotropic network construction, carbon nanoparticle interface anchoring and cross-scale synergistic fixation due to the inability of a single functional component to achieve long-term poor dispersion stability and rapid particle sedimentation and stratification after shutdown. It improves the overall service stability and thermal management reliability of the liquid-cooled composite nanofluid under alternating high-speed pumping and static shutdown conditions.

[0006] In the first aspect, this application provides a highly stable, anti-sagging liquid-cooled composite nanofluid, which contains a continuous phase, a dispersed phase, and a ternary rheological control system. The continuous phase comprises deionized water and 1,2-propanediol, and at 25°C, the volume ratio of the deionized water to 1,2-propanediol is 80:20 to 90:10. The dispersed phase is a composite particle composed of graphene and single-walled carbon nanotubes, and the composite particle accounts for 0.01% to 0.1% of the total mass of the composite nanofluid. The ternary rheology control system is composed of a rheology modifier, polyvinylpyrrolidone, and a polymeric dispersant, wherein the mass ratio of the rheology modifier, polyvinylpyrrolidone, and polymeric dispersant is (0.5-2):(0.5-2):(0.5-2); and the mass ratio of the composite particles to the total mass of the ternary rheology control system is (1.2-2.0):1. The composite nanofluid exhibits thixotropy and anti-sagging properties, and meets the following rheological parameters: The composite nanofluid was subjected to three-stage continuous testing using a rotational rheometer under a constant temperature of 25°C. In the first stage, with 0.1 The shear rate was continuously tested for 60 seconds, and the average value of the last 30 seconds was recorded as the initial low shear viscosity. ; In the second stage, the shear rate is abruptly increased to 100. The shearing was continued for 2 minutes, and the average value of the last 30 seconds was recorded as the high shear viscosity. ; In the third stage, the shear rate is abruptly reduced back to 0.1. After resting for 5 minutes, the average value of the last 30 seconds is recorded as the recovered low shear viscosity. ; The shear-thinning ratio T of the composite nanofluid = / The range is 5 to 15, and its viscosity recovery rate R = ( / η0)×100% is greater than or equal to 90%.

[0007] Optionally, the rheology modifier is selected from at least one of polyurethane derivatives containing bisurea bonds or modified polyurea with hydrophilic groups at the ends.

[0008] Optionally, the polymeric dispersant is a polyurethane copolymer containing an aromatic or heterocyclic carbonophilic anchoring structure, wherein the anchoring structure can undergo π-π interactions or hydrogen bond adsorption with the surface of the composite particles, and the weight-average molecular weight of the polyurethane copolymer is 10,000 to 30,000.

[0009] Optionally, within the composite particles, the mass ratio of graphene to single-walled carbon nanotubes is (1-3):(1-5).

[0010] Optionally, the composite particles account for 0.03% to 0.06% of the total mass of the composite nanofluid.

[0011] Optionally, the single-walled carbon nanotubes have an average diameter of 1 nm to 2 nm and a length of 5 μm to 30 μm; the graphene has a layered structure with 1 to 5 layers.

[0012] Optionally, under constant temperature of 25°C and in the undiluted stock state of the composite nanofluid, its absolute Zeta potential value is measured to be 30 mV to 60 mV using a laser Doppler microelectrophoresis instrument.

[0013] Optionally, the composite nanofluid further comprises a corrosion inhibitor, wherein the corrosion inhibitor accounts for 0.05% to 0.2% of the total mass of the composite nanofluid, and the corrosion inhibitor is selected from benzotriazole or methylbenzotriazole.

[0014] Secondly, this application provides a method for preparing a highly stable, anti-sagging, liquid-cooled composite nanofluid, comprising the following steps: S1. Mix the deionized water and 1,2-propanediol evenly according to the volume ratio to obtain the continuous phase; S2. After premixing the graphene and single-walled carbon nanotubes, add them together to a portion of the continuous phase accounting for 10% to 30% of the total volume of the continuous phase, and perform joint ultrasonic dispersion treatment for 30 to 60 minutes under a power of 200 W to 500 W to obtain a preliminary dispersion of composite particles. S3. Add the rheology modifier, polyvinylpyrrolidone, and polymeric dispersant to the remaining continuous phase, mix and dissolve, and then combine with the initial dispersion of the composite particles; perform high-shear homogenization treatment at 10,000 rpm to 15,000 rpm for 10 to 30 minutes under constant temperature of 25°C, and then let it stand and mature at 25°C for 12 to 24 hours. The resulting composite nanofluid has a shear-thinning ratio T of 5 to 15 and a viscosity recovery rate R greater than or equal to 90%.

[0015] The technical solution provided in this application involves forming a continuous phase from deionized water and 1,2-propanediol at a specific volume ratio, and introducing composite particles composed of graphene and single-walled carbon nanotubes as the dispersed phase at extremely low addition levels (0.01% to 0.1%). Simultaneously, a ternary rheological control system is formed by using a rheology modifier, polyvinylpyrrolidone, and a polymeric dispersant at a specific mass ratio. Through the macroscopic constraint of the total mass ratio of the composite particles to the ternary system, a synergistic mechanism of complementary functions is achieved among the three components in the continuous phase. This ultimately endows the composite nanofluid with thixotropic and anti-sagging properties, simultaneously meeting the requirements of both shear thinning ratio T and viscosity recovery rate R. Due to the synergistic constraints of the above-mentioned technical features at the levels of composition, proportion, and performance characterization, this invention achieves low flow resistance during high-speed pumping, rapid viscosity reconstruction during static shutdown, and long-term colloidal dispersion stability at extremely low particle concentrations within a single formulation system, breaking through the inherent bottleneck of mutual constraint between thermal conductivity and dispersion stability in existing technologies.

[0016] The ternary rheological control system adopted in this application, composed of rheology modifier, polyvinylpyrrolidone, and polymeric dispersant, is not a simple superposition of the functions of each component. Instead, it achieves a deep coupling of "interfacial stability" and "structural support" through cross-scale interfacial interactions and the construction of a macroscopic spatial network. Its specific synergistic mechanism is as follows: Microscopic-level interfacial stability and particle dispersion: In composite nanofluids, polymeric dispersants, through their aromatic or heterocyclic carbonophilic anchoring structures, physically adsorb onto the surfaces of carbon nanomaterials (graphene, single-walled carbon nanotubes) via π-π interactions or hydrogen bonds. This adsorption firmly anchors the nanoparticles to the dispersant molecules, thereby suppressing agglomeration caused by van der Waals forces between particles. Furthermore, polyvinylpyrrolidone, through the hydrophilic properties of its polymer segments, works in conjunction with the dispersant to form a dense solvation protective layer on the particle surface. This protective layer significantly slows down particle aggregation and sedimentation through steric hindrance, ensuring uniform dispersion of particles in the liquid phase and preventing re-agglomeration due to strong interparticle interactions. Mesoscopic Structural Complementarity and Dynamic Equilibrium: Due to the extremely high aspect ratio of single-walled carbon nanotubes (SUVs), they readily form loosely entangled physical networks in fluids. The introduction of polyvinylpyrrolidone (PVP) can regulate the dispersion state of SUVs, thereby affecting the network structure, preventing macroscopic flocculation caused by excessive particle entanglement, and aiding in the slippage and deagglomeration of the structure during high-speed pumping shearing of the fluid. This directly contributes to the fluid's performance at 100°C. Low flow resistance at shear rates; Macroscopic Thixotropic Networks and Rapid Reconstruction: Rheology modifiers self-assemble into a dense, high-modulus three-dimensional thixotropic framework within the continuous phase through strong hydrogen bonding. This framework effectively embeds dispersed composite particles into the thixotropic network, providing sufficient yield stress to resist concentration gradient sedimentation caused by gravity, thereby endowing the fluid with excellent anti-sagging properties. The key to synergistic effect: After the system undergoes high shear failure, this ternary system exhibits extremely high structural recovery efficiency: the rheology modifier is responsible for rapidly rebuilding the macroscopic viscosity framework, while the polymeric dispersant and polyvinylpyrrolidone ensure that the particles do not collide and cause irreversible aggregation during network reconstruction. This synergistic mechanism ensures that the composite nanofluid can stably achieve a viscosity recovery rate R of over 90% while meeting the shear thinning ratio T (5 to 15), thus completely solving the technical bottleneck of rapid particle sedimentation in traditional single or two-component systems under the static state of a liquid-cooled system in shutdown condition.

[0017] Liquid cooling systems are characterized by alternating high-speed pumping and frequent start-stop cycles. This application scenario places dual dynamic requirements on the cooling medium, namely shear response and structural recovery. This invention uses T-value and R-value as core performance parameters to directly link the rheological properties of the material with the actual operating requirements of the liquid cooling system. This upgrades the design logic of composite nanofluids from simple component ratio optimization to performance-oriented design for service conditions, thereby achieving efficient heat dissipation during long-term operation. Attached Figure Description

[0018] To more clearly illustrate the technical solutions of the embodiments of the present invention, the drawings used in the description of the embodiments will be briefly introduced below. Obviously, the drawings described below are some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0019] Figure 1 This is a schematic flowchart of the preparation method of the highly stable, anti-sagging liquid-cooled composite nanofluid in this application. Detailed Implementation

[0020] I. Raw Material Description Graphene: Single to five-layer sheet structure, average lateral size 1-10 μm, carbon content ≥99wt%, oxygen content <1wt%; can be prepared by chemical vapor deposition or liquid phase exfoliation, or directly using commercially available products that meet the above specifications.

[0021] Single-walled carbon nanotubes (SWCNTs): average diameter 1-2 nm, length 5-30 μm, purity ≥95 wt%, and metal residual catalyst content <3 wt%.

[0022] Deionized water: resistivity ≥18MΩ·cm, TOC (total organic carbon) <10ppb.

[0023] 1,2-Propanediol: CAS No. 57-55-6, industrial grade, purity ≥99.5wt%, moisture content <0.1wt%.

[0024] Rheology modifiers: polyurethane derivatives containing diurea bonds, such as BYK-410 (BYK Chemicals) or functionally equivalent commercial products; or modified polyureas with hydrophilic groups at the ends, such as DISPARLON6900-20X (Kushu Chemicals) or functionally equivalent commercial products.

[0025] Polyvinylpyrrolidone (PVP): K30 type, weight average molecular weight approximately 40,000 g / mol, purity ≥ 99 wt%.

[0026] Polymer dispersants: Polyurethane copolymers containing aromatic or heterocyclic carbon-loving anchoring structures, with a weight-average molecular weight (Mw) of 10,000–30,000 g / mol, such as BYK-2013 (BYK Chemicals) or functionally equivalent commercial products.

[0027] Corrosion inhibitor: Benzotriazole (BTA), CAS No. 95-14-7, purity ≥99wt%; or methylbenzotriazole (TTA), CAS No. 136-85-6, purity ≥99wt%.

[0028] II. Unified Testing Method for Rheological Properties The rheological properties of all embodiments and comparative examples of this invention were measured using the following standardized procedure to ensure the uniqueness and repeatability of the data.

[0029] Test instrument: Rotational rheometer (Anton Paar MCR302 or TA Instruments DHR-2, or equivalent precision instrument), equipped with a coaxial cylindrical geometry (CC27 type or equivalent).

[0030] Temperature control conditions: Peltier circulating water bath temperature control, test temperature 25±0.1℃; samples were allowed to stand in a constant temperature chamber at 25℃ for no less than 2 hours before testing to achieve equilibrium.

[0031] First stage (initial low-shear stage): with a rate of 0.1 The sample was subjected to a shear rate for 60 seconds, and the arithmetic mean of all data points in the last 30 seconds was recorded as the initial low-shear viscosity. (Unit: mPa·s). If the viscosity change rate exceeds 5% within the interval from 30 seconds to 60 seconds, the average of the steady-state plateau segment with a measured viscosity change rate below 5% shall be used as the mean. And note this in the data remarks.

[0032] Second stage (high shear failure stage): The shear rate is abruptly increased to 100. The shearing was continued for 2 minutes, and the arithmetic mean of all data points in the last 30 seconds was recorded as the high shear viscosity. (Unit: mPa·s).

[0033] The third stage (structural recovery stage): abruptly reducing the shear rate back to 0.1. After resting for 5 minutes, the arithmetic mean of all data points within the last 30 seconds is recorded as the recovered low shear viscosity. (Unit: mPa·s).

[0034] Calculation index: Shear thinning ratio T= / Viscosity recovery rate R = ( / η0)×100%.

[0035] three, Steady-state verification experiment To demonstrate that the first-stage 60-second test duration can reliably capture the steady-state η0 value for all formulation ranges of this invention, the sample from Example 1 is used as a representative example, at 0.1 A viscosity-time tracking test was conducted at the shear rate for up to 120 seconds, and the results are shown in Table 1.

[0036] Table 1 Example 1 at 0.1 Viscosity-time tracking data at shear rate

[0037] As shown in Table 1, the sample in Example 1 was at 0.1 At the shear rate, the viscosity reached a plateau within approximately 40–50 seconds. The viscosity change rate from 50 to 120 seconds was less than 1%, far below the steady-state threshold (5%). The viscosity change rate from 30 to 60 seconds was 3.8%, within an acceptable range. Taking the average of the last 30 seconds (30–60 seconds), η0 = 244.7 mPa·s was obtained, with a relative deviation of 1.5% from the average of 248.3 mPa·s from 60 to 120 seconds, which is within the engineering testing error range. These results demonstrate that a 60-second test duration (taking the average of the last 30 seconds) can reliably capture steady-state conditions for the entire formulation range covered by this invention. The test method has sufficient repeatability.

[0038] IV. Preparation of Each Example and Comparative Example Please see Figure 1 This is a schematic diagram of the preparation method of the highly stable, anti-sagging liquid-cooled composite nanofluid in this application; Example 1 (Baseline formulation, ternary system rheology modifier: PVP: polymeric dispersant = 1:1:1, graphene: SWCNT = 1:1) S1, Base Liquid Preparation Measure deionized water and 1,2-propanediol, mix them in a beaker at a volume ratio of 85:15, and stir magnetically at 300 rpm for 10 minutes until fully homogeneous to obtain a continuous phase (total volume is denoted as V).

[0039] S2, Dispersed Phase Preparation Graphene and single-walled carbon nanotubes were weighed at a ratio of 1:1, comprising 0.05 wt% of the total mass of the composite nanofluid. After thorough premixing and grinding, they were transferred together into a continuous phase comprising 20% ​​(0.2V) of the total continuous phase volume. The mixture was placed in an ice-water bath and ultrasonically dispersed for 45 minutes at 350W using an ultrasonic homogenizer (20mm probe diameter) (operating mode: alternating 2-second ultrasonic waves followed by 3-second intervals to prevent sample temperature rise from exceeding 10℃) to obtain a preliminary dispersion of the composite particles, which was then set aside for later use.

[0040] S3, System Construction and Maturation Weigh out the rheology modifier, PVP, and polymeric dispersant separately, in a mass ratio of 1:1:1, controlling the total amount of the ternary rheology control system so that the mass ratio of the composite particles to the total mass of the ternary system is approximately 1.5:1 (i.e., the total amount of the ternary system is approximately 2 / 3 of the total amount of the composite particles). Add the three components to the remaining 80% continuous phase (i.e., 0.8V), and magnetically stir at 300 rpm for 40 minutes at 25°C until all three components are completely dissolved to obtain a ternary system solution. Combine the ternary system solution with the initial dispersion of composite particles obtained in step S2, and perform high-shear homogenization at 12000 rpm for 15 minutes at a constant temperature of 25°C (start timing after the power output of the homogenizer probe stabilizes). After homogenization, transfer the sample to a 25°C constant temperature oven and allow it to stand for 18 hours to mature, thus obtaining the composite nanofluid of Example 1.

[0041] Example 2 (Graphene surplus end, graphene:SWCNT = 3:1) Except for step S2, where the mass ratio of graphene to single-walled carbon nanotubes is adjusted to 3:1 (graphene accounts for 75% of the total mass of the composite particles and SWCNTs account for 25%), the remaining steps, the amount of each component, and the process parameters are exactly the same as in Example 1.

[0042] Example 3 (SWCNT surplus end, graphene:SWCNT = 1:5) Except for step S2, where the mass ratio of graphene to single-walled carbon nanotubes is adjusted to 1:5 (graphene accounts for 16.7% of the total mass of the composite particles, and SWCNTs account for 83.3%), the remaining steps, the amount of each component, and the process parameters are exactly the same as in Example 1.

[0043] Example 4 (Ternary system extreme ratio one, rheology modifier surplus, 2:0.5:0.5) Except for step S3, where the mass ratio of rheology modifier, PVP, and polymeric dispersant is adjusted to 2:0.5:0.5 (rheology modifier accounts for 66.7% of the total mass of the ternary system, and PVP and polymeric dispersant each account for 16.7%), the total amount of the ternary system remains unchanged, and the ratio of composite particles to the total mass of the ternary system is maintained at approximately 1.5:1. The remaining steps are exactly the same as in Example 1.

[0044] Example 5 (Ternary system extreme ratio 2, PVP surplus, 0.5∶2∶0.5) Except for step S3, where the mass ratio of rheology modifier, PVP, and polymeric dispersant is adjusted to 0.5:2:0.5 (PVP accounts for 66.7% of the total mass of the ternary system, and the rheology modifier and polymeric dispersant each account for 16.7%), the other conditions are exactly the same as in Example 4.

[0045] Example 6 (Ternary system extreme ratio 3, with excess polymeric dispersant, 0.5:0.5:2) Except for step S3, where the mass ratio of rheology modifier, PVP, and polymeric dispersant is adjusted to 0.5:0.5:2 (polymeric dispersant accounts for 66.7% of the total mass of the ternary system, and rheology modifier and PVP each account for 16.7%), the other conditions are exactly the same as in Example 4.

[0046] Example 7 (Formulation containing corrosion inhibitor) Based on Example 1, in step S1, benzotriazole (BTA) accounting for 0.1 wt% of the total mass of the composite nanofluid was added to the mixture of deionized water and 1,2-propanediol. After magnetic stirring at 300 rpm until BTA was completely dissolved (about 5 minutes), steps S2 and S3 were continued. The remaining process parameters were exactly the same as in Example 1.

[0047] Comparative Example 1 (rheology modifier omitted, binary system of PVP + polymeric dispersant) In step S3, no rheology modifier is added; only PVP and a polymeric dispersant (mass ratio of 1:1) are used to form a binary dispersion system. To ensure the validity of the comparison, the total amount of the binary system is exactly the same as the total amount of the ternary system in Example 1 (the mass ratio of composite particles to the total mass of the binary system is maintained at 1.5:1), and the remaining steps are exactly the same as in Example 1.

[0048] Comparative Example 2 (using only the PVP single-component system) In step S3, no rheology modifier or polymeric dispersant is added; only PVP is used as the single component. The total amount of PVP used is exactly the same as the total amount of the ternary system in Example 1, and the remaining steps are exactly the same as in Example 1.

[0049] Comparative Example 3 (omitting polymeric dispersant, rheology modifier + PVP binary system) In step S3, no polymeric dispersant is added; only rheology modifier and PVP (mass ratio 1:1) are used. The total amount of the binary system is the same as that of the ternary system in Example 1, and the remaining steps are exactly the same as in Example 1.

[0050] Comparative Example 4 (PVP omitted, binary system of rheology modifier + polymeric dispersant) In step S3, PVP is not added; only a rheology modifier and a polymeric dispersant (mass ratio 1:1) are used. The total amount of the binary system is the same as that of the ternary system in Example 1, and the remaining steps are exactly the same as in Example 1.

[0051] Note: Comparative Examples 1 to 4 cover all cases in ternary systems where each single component is omitted in turn (including three binary systems with omitted rheology modifiers, omitted polymeric dispersants, and omitted PVP, as well as the single-component limit case using only PVP), which is sufficient to demonstrate the irreplaceable synergistic effect of ternary systems from multiple dimensions.

[0052] V. Experimental Results and Analysis (I) Summary of formulation parameters for each embodiment and comparative example Table 2 Summary of formulation parameters for each embodiment and comparative example

[0053] (II) Rheological property test results The rheological properties of each sample were measured according to the unified 3ITT test procedure specified in Section 2 of this instruction manual, and the results are shown in Table 3.

[0054] Table 3. ITT rheological test results for each embodiment and comparative example 3.

[0055] The analysis is as follows: First, Examples 1 to 6 cover the two extreme values ​​(3:1 and 1:5) of the graphene to SWCNT mass ratio defined by the present invention, as well as the three extreme ratios (2:0.5:0.5, 0.5:2:0.5, 0.5:0.5:2) of the internal proportions of the ternary rheological control system. The T values ​​of all samples fall within the range of 5 to 15, and the R values ​​are not less than 90%, which fully demonstrates that the parameter range protected by the present invention is technically fully feasible. The specification provides sufficient support for the entire technical solution range of the present invention.

[0056] Second, the T values ​​of Comparative Example 1 (omitting the rheology modifier) ​​and Comparative Example 2 (PVP single component only) are close to 1 (1.1 and 1.2 respectively), and the R value is only about 40%. This indicates that under the condition that no rheology modifier is involved in the construction of the macroscopic thixotropic framework, the system does not have thixotropic and viscosity recovery capabilities at all, which confirms the irreplaceable nature of the rheology modifier as a framework component.

[0057] Third, although Comparative Examples 3 (omitting the polymeric dispersant) and 4 (omitting PVP) had certain shear-thinning ratios (T values ​​of 9.4 and 7.9, respectively, falling within the target range), their viscosity recovery rates R were only 74.2% and 70.7%, respectively, both below the required threshold of 90%. This result reveals that after high shear failure, the skeletal network provided solely by the rheology modifier, lacking the interfacial anchoring and steric hindrance protection of PVP and the polymeric dispersant for the carbon nanoparticles, leads to partial irreversible aggregation of the particles during high shear, resulting in incomplete viscosity recovery after high shear failure. The three components must coexist synergistically to simultaneously meet the requirements of both T and R parameters, proving that the synergistic effect of the ternary system is inseparable.

[0058] Fourth, the T and R values ​​of Example 7 (containing BTA corrosion inhibitor formulation) are basically the same as those of Example 1 (T=11.1, R=96.3%), indicating that the introduction of corrosion inhibitor does not interfere with the function of the ternary rheological control system and the two have good compatibility.

[0059] (III) Long-term dispersion stability test Each sample was sealed in a transparent glass container and stored at a constant temperature of 25°C. Samples were taken on days 1, 7, 14, and 30, and the volume average particle size D of the composite particles was determined using a laser particle size analyzer. 50 The absolute zeta potential of the undiluted stock solution was measured at 25°C using a laser Doppler microelectrophoresis apparatus (Malvern Zetasizer Nano ZS or equivalent instrument), and the sedimentation and stratification were observed visually. The results are shown in Table 4.

[0060] Table 4. Results of long-term stability test of each sample after standing at 25℃ for 30 days.

[0061] As shown in Table 4, after 30 days of standing, the particle size growth rate of Examples 1 to 6 was less than 10%, and the absolute Zeta potential value remained above 38 mV (higher than the colloidal stability threshold of 30 mV). No visible sedimentation or stratification was observed, proving that under the synergistic effect of the ternary rheological control system, the composite particles could maintain long-term colloidal stability in the continuous phase, and their absolute Zeta potential value met the technical indicator of 30 mV to 60 mV specified in this invention. Comparative Examples 1 and 2 experienced severe particle aggregation and sedimentation within 30 days, with particle size increasing more than 5 times and the absolute Zeta potential value dropping below 10 mV. A clear solid sedimentation layer appeared at the bottom, proving that relying solely on PVP or a two-component system could not achieve the long-term dispersion stability required by this invention. Although Comparative Examples 3 and 4 were superior to Comparative Examples 1 and 2, the particle size growth still exceeded 150%, the Zeta potential dropped to approximately 23 mV, and slight visible stratification appeared, also failing to meet the stability requirements of this invention, further confirming the necessity of the ternary synergistic system.

[0062] (iv) Anti-settlement stratification performance test The anti-sagging property claimed in this invention has the following core technical meaning in liquid cooling applications: When the liquid cooling system is in a stopped and static state, the composite nanofluid provides three-dimensional static support for the carbon nanocomposite particles through a high-viscosity thixotropic network established by the ternary rheological control system under low shear and static conditions. This prevents the particles from settling and stratifying due to the concentration gradient caused by density difference in the gravitational field, maintains the uniform dispersion state of the composite nanofluid, and ensures the stability of the thermal conductivity performance after the liquid cooling system is restarted.

[0063] To directly characterize the above properties, the following method was used for testing: Each sample was injected into a stoppered transparent glass graduated cylinder with an inner diameter of 25 mm and a height of 150 mm to the 100 mm mark. After sealing, it was placed vertically at 25°C. The bottom sedimentation and stratification height was recorded at 30 minutes, 60 minutes, 120 minutes, and 24 hours (based on the color boundary line that can be observed with the naked eye). Each sample was then uniformly coated on an aluminum alloy polished plate with a surface roughness Ra < 0.4 μm (coating thickness of about 200 μm), fixed at a 60° tilt angle, and placed at 25°C for 30 minutes. The sample sag displacement length was recorded. The results are shown in Table 5.

[0064] Table 5 Results of static anti-settlement stratification and inclined plate sag tests for each sample

[0065] Table 5 shows that in Examples 1 to 6, no visible bottom sedimentation stratification (<0.5 mm) was observed within 30 minutes of standing. After 24 hours of standing, the sedimentation height did not exceed 2.5 mm, and the sag displacement on the inclined plate did not exceed 6 mm, proving that the thixotropic network established by the ternary system has effective static support capability for the composite particles. Comparative Examples 1 and 2, lacking thixotropy (T≈1, R≈40%), showed rapid sedimentation in the gravitational field, with obvious sedimentation stratification of 8–11 mm appearing within 30 minutes. In the inclined plate test, all samples sag to the bottom, confirming the thermodynamically inevitable sedimentation trend of carbon nanoparticles without thixotropic network protection. Comparative Examples 3 and 4, due to R values ​​not reaching the 90% threshold, showed incomplete reconstruction of the thixotropic network during the restorative process, resulting in insufficient particle support and moderate sedimentation stratification (settlement height approximately 10–12 mm after 24 hours) and significant sag displacement (approximately 18–23 mm). The above data establishes a direct quantitative correlation between the dual-parameter constraints of T and R values ​​and the macroscopic anti-settlement stratification performance, proving that T∈[5,15] and R≥90% as specified in this invention are the necessary and sufficient conditions for ensuring the anti-sagging performance of this invention.

[0066] (v) Corrosion Inhibition Performance Test (Example 7) Copper sheets (20×10×1mm, purity ≥99.9%), aluminum alloy sheets (6061 type, 20×10×1mm), and stainless steel sheets (304 type, 20×10×1mm) were polished with 2000-grit sandpaper, ultrasonically cleaned with anhydrous ethanol, and accurately weighed. They were then immersed in the composite nanofluid samples of Example 1 (without corrosion inhibitor) and Example 7 (containing 0.1wt% BTA), respectively. After standing and soaking at 25℃ for 168 hours (7 days), they were taken out, cleaned, dried, and weighed again. The corrosion weight loss rate (mg / cm²·h) was calculated, and the results are shown in Table 6.

[0067] Table 6 Comparison of corrosion weight loss rates of the three metals in Examples 1 and 7

[0068] As shown in Table 6, Example 7 containing 0.1 wt% BTA exhibits corrosion inhibition efficiencies exceeding 90% for both copper and aluminum alloy sheets, and over 80% for stainless steel sheets. This demonstrates that benzotriazole effectively inhibits corrosion in the formulation system of this invention, significantly improving the compatibility of the composite nanofluid with the metal materials of the liquid cooling system, thus achieving the technical objective of the corrosion inhibitor formulation of this invention.

[0069] Based on all the experimental data from the above embodiments and comparative examples, the following conclusions can be drawn: First, the ternary rheological control system (rheology modifier + PVP + polymeric dispersant) proposed in this invention is a necessary condition for achieving the dual parameter requirements of T∈[5,15] and R≥90% for composite nanofluids. The absence of any component will result in one or two parameters failing to meet the standard, and the synergistic effect of the ternary system is irreplaceable.

[0070] Second, within the formulation range defined by this invention (including the extreme values ​​of the graphene:SWCNT ratio at both ends of 1:5 and 3:1, and the three extreme ratios within the ternary system), all embodiments satisfy the rheological parameter conditions, proving that the specification fully supports the entire technical solution range of this invention and that the technical solution range is feasible.

[0071] Third, there is a clear quantitative correlation between the dual-parameter constraints of T value and R value and the macroscopic anti-settling stratification performance. T∈[5,15] and R≥90% are the necessary and sufficient conditions to ensure the anti-particle settling stratification performance of the present invention under the state of static cooling system shutdown. The anti-sagging property in the title of the invention has a clear technical connotation and a measurable characterization standard.

[0072] Fourth, the introduction of corrosion inhibitors does not affect the function of the ternary rheological control system. The corrosion inhibition efficiency of the formulation containing corrosion inhibitors for commonly used metal materials in liquid cooling systems reaches more than 80%, which significantly improves the engineering application applicability of composite nanofluids.

Claims

1. A highly stable, anti-sagging, liquid-cooled composite nanofluid, characterized in that, Its internal components include a continuous phase, a dispersed phase, and a ternary rheological control system; The continuous phase comprises deionized water and 1,2-propanediol, and at 25°C, the volume ratio of the deionized water to 1,2-propanediol is 80:20 to 90:

10. The dispersed phase is a composite particle composed of graphene and single-walled carbon nanotubes, and the composite particle accounts for 0.01% to 0.1% of the total mass of the composite nanofluid. The ternary rheology control system is composed of a rheology modifier, polyvinylpyrrolidone, and a polymeric dispersant, wherein the mass ratio of the rheology modifier, polyvinylpyrrolidone, and polymeric dispersant is (0.5-2):(0.5-2):(0.5-2); and the mass ratio of the composite particles to the total mass of the ternary rheology control system is (1.2-2.0):

1. The composite nanofluid exhibits thixotropy and anti-sagging properties, and meets the following rheological parameters: The composite nanofluid was subjected to three-stage continuous testing using a rotational rheometer under a constant temperature of 25°C. In the first stage, with 0.1 The shear rate was continuously tested for 60 seconds, and the average value of the last 30 seconds was recorded as the initial low shear viscosity. ; In the second stage, the shear rate is abruptly increased to 100. The shearing was continued for 2 minutes, and the average value of the last 30 seconds was recorded as the high shear viscosity. ; In the third stage, the shear rate is abruptly reduced back to 0.

1. After resting for 5 minutes, the average value of the last 30 seconds is recorded as the recovered low shear viscosity. ; The shear-thinning ratio T of the composite nanofluid = / The range is 5 to 15, and its viscosity recovery rate R = ( / η0)×100% is greater than or equal to 90%.

2. The highly stable, anti-sagging, liquid-cooled composite nanofluid according to claim 1, characterized in that, The rheology modifier is selected from at least one of polyurethane derivatives containing bisurea bonds or modified polyurea with hydrophilic groups at the ends.

3. The highly stable, anti-sagging, liquid-cooled composite nanofluid according to claim 1 or 2, characterized in that, The polymeric dispersant is a polyurethane copolymer containing an aromatic or heterocyclic carbonophilic anchoring structure. The anchoring structure can interact with the surface of the composite particles through π-π interactions or hydrogen bonding adsorption, and the weight-average molecular weight of the polyurethane copolymer is 10,000 to 30,000.

4. The highly stable, anti-sagging, liquid-cooled composite nanofluid according to claim 1, characterized in that, Inside the composite particles, the mass ratio of graphene to single-walled carbon nanotubes is (1-3):(1-5).

5. The highly stable, anti-sagging, liquid-cooled composite nanofluid according to claim 1, characterized in that, The composite particles account for 0.03% to 0.06% of the total mass of the composite nanofluid.

6. The highly stable, anti-sagging, liquid-cooled composite nanofluid according to claim 1, characterized in that, The single-walled carbon nanotubes have an average diameter of 1 nm to 2 nm and a length of 5 μm to 30 μm; the graphene has a layered structure with 1 to 5 layers.

7. The highly stable, anti-sagging, liquid-cooled composite nanofluid according to claim 1, characterized in that, When the composite nanofluid is kept at a constant temperature of 25°C and is in an undiluted stock solution, its absolute zeta potential value is measured to be 30 mV to 60 mV using a laser Doppler microelectrophoresis apparatus.

8. The highly stable, anti-sagging, liquid-cooled composite nanofluid according to claim 1, characterized in that, The composite nanofluid further comprises a corrosion inhibitor, which accounts for 0.05% to 0.2% of the total mass of the composite nanofluid, and the corrosion inhibitor is selected from benzotriazole or methylbenzotriazole.

9. A method for preparing a highly stable, anti-sagging, liquid-cooled composite nanofluid as described in any one of claims 1 to 8, characterized in that, Includes the following steps: S1. Mix the deionized water and 1,2-propanediol evenly according to the volume ratio to obtain the continuous phase; S2. After premixing the graphene and single-walled carbon nanotubes, add them together to a portion of the continuous phase accounting for 10% to 30% of the total volume of the continuous phase, and perform joint ultrasonic dispersion treatment for 30 to 60 minutes under a power of 200 W to 500 W to obtain a preliminary dispersion of composite particles. S3. Add the rheology modifier, polyvinylpyrrolidone, and polymeric dispersant to the remaining continuous phase, mix and dissolve, and then combine with the initial dispersion of the composite particles; perform high-shear homogenization treatment at 10,000 rpm to 15,000 rpm for 10 to 30 minutes under constant temperature of 25°C, and then let it stand and mature at 25°C for 12 to 24 hours. The resulting composite nanofluid has a shear-thinning ratio T of 5 to 15 and a viscosity recovery rate R greater than or equal to 90%.

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