Polymer brush functionalized liquid metal nanolubricant additives, methods of making and using the same

Abstract

The application discloses a kind of polymer brush functionalized liquid metal nanometer lubricating additive and its preparation method and application.The additive includes gallium indium liquid metal nanometer droplet and poly (lauryl methacrylate) -block-poly (acrylic acid) diblock copolymer grafted on its surface by coordination interaction.The preparation method includes: first, poly (lauryl methacrylate) -block-poly (acrylic acid) diblock copolymer is synthesized by atom transfer radical polymerization method;Then gallium indium liquid metal is mixed with the tetrahydrofuran solution of the block copolymer, and polymer brush functionalized liquid metal nanometer droplet is obtained by ultrasonic treatment.The application realizes the effective regulation of liquid metal nanometer droplet size by regulating the composition of block copolymer.The additive has excellent dispersion stability in base oil, and compared with base oil PAO10, the average friction coefficient is reduced by 47.0% at very low additive amount (0.1 wt%), the wear volume is reduced by 82.1%-92.8%, and excellent friction reduction and wear resistance are shown, which can be widely applied to the lubrication system of mechanical equipment.

Description

Technical Field

[0001] This invention relates to the field of lubricant additive technology, specifically to a polymer-functionalized liquid metal nano lubricant additive for brushes, its preparation method, and its friction-reducing applications. Background Technology

[0002] Friction and wear are unavoidable physical processes in mechanical systems. Globally, approximately 23% of primary energy consumption originates from frictional contact, and about 80% of mechanical component failures are caused by wear. Lubrication is the most effective means of controlling friction and reducing wear. Lubricating additives, as the essence of lubricating oils, play an irreplaceable role in improving the friction-reducing and anti-wear properties, load-bearing capacity, and adaptability to extreme working conditions of base oils. However, the performance limitations of traditional lubricating additives under harsh conditions such as high temperatures and heavy loads are becoming increasingly apparent. Developing novel, highly efficient, environmentally friendly nano-lubricating additives adapted to extreme conditions has become an important research direction in the field of tribology.

[0003] Gallium-based liquid metals have attracted widespread interest from researchers due to their unique properties. From a lubrication perspective, gallium-based liquid metals possess characteristics such as low melting point, low vapor pressure, low toxicity, good fluidity, high thermal stability, high thermal conductivity, and good extreme pressure performance, meeting the requirements of green lubricants. Studies have found that compared with other lubricants such as oils, greases, and ionic liquids, gallium-based liquid metals exhibit superior lubrication performance under some extreme conditions (high temperature, extreme pressure, and electric field).

[0004] For example, Li H, Tian P, Lu H, et al. State-of-the-art of extremepressure lubrication realized with thehigh thermal diffusivity of liquidmetal [J]. ACS applied materials&interfaces (2017, 9(6): 5638-44.) Utilizing the high thermal diffusivity of liquid metals, advanced extreme pressure lubrication has been achieved, with performance two orders of magnitude higher than that of conventional organic lubricants. In a four-ball test, the extreme pressure lubrication characteristics of gallium-based liquid metals were compared with gear oils and polyalphaolefins. At a speed of 1800 rpm and under extremely high loads (10 kN), the liquid metals exhibited excellent lubrication performance, far superior to traditional organic lubricants. Therefore, gallium-based liquid metals can be used as an extreme pressure lubricant, effectively preventing welding of sliding interfaces through the synergistic effect of ultra-fast heat dissipation and reduced friction coefficient.

[0005] In addition, Cheng et al. (Cheng J, Yu Y, Guo J, et al. Ga-based liquid metal with good self-lubricity and highload-carrying capacity [J]. Tribology International (2019, 129: 1-4.) Gallium-based room-temperature liquid metals were found to exhibit good lubricity and high load capacity (1500 kN) on steel-ceramic pairs over a wide load range, significantly outperforming other liquid lubricants such as oils and ionic liquids. When sliding with Si3N4 balls within a load range of 100-1500 N, gallium-based liquid metals provided a low coefficient of friction (0.11-0.23) and a low wear rate (10 kN / kg). -8 ~10 -7 mm 3 / Nm).

[0006] Although gallium-based liquid metals possess excellent lubricating properties, their dispersion stability in base oils is poor, and they are prone to sedimentation and aggregation, limiting their direct application as lubricant additives. To address this issue, researchers have attempted to functionalize liquid metal nanodroplets through surface modification.

[0007] Guo et al. (Guo J, Cheng J, Tan H, et al. Constructing a novel and high-performance liquid nanoparticle additive from a Ga-based liquid metal[J]. Nanoscale (2020, 12(16): 9208-18.) 1-Dodecylthiol-modified liquid metal nanodroplets were prepared using an ultrasonic-assisted method, resulting in functionalized liquid metal nanodroplets. In terms of tribological properties, these functionalized liquid metal nanodroplets exhibited good dispersion stability in PAO10 oil and demonstrated excellent friction-reducing and wear-resistant properties. When the additive concentration in PAO10 was 0.17 wt%, the coefficient of friction decreased by 39% and the wear rate decreased by 93% compared to using pure PAO10.

[0008] He et al. (He B, Liu S, Zhao X, et al. Dialkyl dithiophosphate-functionalized gallium-based liquid-metal nanodroplets aslubricant additives for antiwear and friction reduction [J]. ACS Applied Nano Materials (2020, 3(10): 10115-22.) Dialkyl dithiophosphate functionalized liquid metal nanodroplets were obtained by surface modification. Since the modification of DDP helps to improve the dispersibility of liquid metal nanodroplets in base lubricating oil PAO, it can significantly reduce the friction coefficient and wear volume of the friction pair surface when used as a base oil additive.

[0009] However, the aforementioned surface modification methods mainly employ small-molecule modifiers, whose molecular structures are relatively simple, limiting their ability to regulate the dispersion stability and lubrication performance of liquid metal nanodroplets. Small-molecule modified layers often suffer from insufficient stability and are prone to detachment during friction, making it difficult to maintain lubrication under harsh operating conditions. Furthermore, existing technologies lack effective means for controlling the size of liquid metal nanodroplets, while the size of nanodroplets significantly influences their tribological properties.

[0010] Therefore, developing a novel liquid metal lubricant additive that can effectively improve the dispersion stability of liquid metal nanodroplets in base oil, achieve controllable adjustment of nanodroplet size, and possess excellent friction-reducing and anti-wear properties is of great research significance and application value. Summary of the Invention

[0011] The present invention aims to provide a polymer brush functionalized liquid metal nano lubricant additive, its preparation method and application, to solve the technical problems of poor dispersion stability, difficulty in size control and easy shedding of small molecule modification layer in base oil, which leads to decreased lubrication performance of existing liquid metal lubricants.

[0012] To achieve the above objectives, the present invention provides the following technical solution: A polymer brush-functionalized liquid metal nanolubricant additive comprises gallium indium liquid metal nanodroplets and a poly(lauryl methacrylate)-block-poly(acrylic acid) diblock copolymer grafted onto its surface through coordination interactions; the poly(acrylic acid) blocks in the poly(lauryl methacrylate)-block-poly(acrylic acid) diblock copolymer contain carboxyl groups, and the carboxyl groups form a stable bond with the gallium oxide layer on the surface of the gallium indium liquid metal nanodroplets through coordination interactions, thereby forming a polymer brush structure on the surface of the liquid metal nanodroplets.

[0013] Preferably, in the poly(lauryl methacrylate)-block-poly(acrylic acid) diblock copolymer, the ratio of the degree of polymerization of the poly(lauryl methacrylate) block to the poly(acrylic acid) block is 0.5:1 to 2:1.

[0014] Preferably, the average particle size of the gallium-indium liquid metal nanodroplets is 100-900 nm.

[0015] This invention also provides a method for preparing the above-mentioned polymer brush functionalized liquid metal nano-lubricant additive, comprising the following steps: (1) Synthesis of poly(lauryl methacrylate)-block-poly(acrylic acid) diblock copolymer: (1a) Atom transfer radical polymerization was used, with lauryl methacrylate as monomer, ethyl α-bromoisobutyrate as initiator, copper bromide (CuBr2) as catalyst, tris(2-dimethylaminoethyl)amine (Me6TREN) as ligand, and tin(II) 2-ethylhexanoate (Sn(EH)2) as reducing agent. The reaction was carried out in anisole solvent at 50-70℃. After precipitation and drying, a macromolecular initiator: poly(lauryl methacrylate)-bromine (PLMA-Br) was obtained. The molar ratio of lauryl methacrylate, ethyl α-bromoisobutyrate, CuBr2, Me6TREN, and Sn(EH)2 is (50~150):1:(0.02~0.06):(0.1~0.3):(0.1~0.3). (1b) Using atom transfer radical polymerization, the macromolecular initiator obtained in step (1a) and tert-butyl acrylate were used as monomers, copper bromide was used as catalyst, tris(2-dimethylaminoethyl)amine was used as ligand, and tin(II) 2-ethylhexanoate was used as reducing agent. The reaction was carried out in anisole solvent at 50-70℃, and after precipitation and drying, a block copolymer was obtained: poly(lauryl methacrylate)-b-poly(tert-butyl acrylate) (PLMA-b-PtBA); In step (1b), the molar ratio of tert-butyl acrylate, PLMA-Br, CuBr2, Me6TREN and Sn(EH)2 is (50~150):1:(0.02~0.06):(0.1~0.3):(0.1~0.3). (1c) Dissolve the block copolymer obtained in step (1b) in dichloromethane, add excess trifluoroacetic acid, and hydrolyze at room temperature for 24-72 hours to completely hydrolyze the tert-butyl groups in the poly(tert-butyl acrylate) blocks into carboxyl groups. After precipitation and drying, poly(lauryl methacrylate)-block-poly(acrylic acid) diblock copolymer (PLMA-b-PAA) is obtained. (2) The gallium indium liquid metal is mixed with the tetrahydrofuran solution of poly(lauryl methacrylate)-block-poly(acrylic acid) diblock copolymer obtained in step (1c), and ultrasonically treated in an ice-water bath for 30-120 minutes to obtain poly(lauryl methacrylate)-block-poly(acrylic acid) functionalized gallium indium liquid metal nanodroplets, namely the polymer brush functionalized liquid metal nanolubricant additive; The mass ratio of gallium indium liquid metal to poly(lauryl methacrylate)-block-poly(acrylic acid) diblock copolymer is (10-30):1, and the concentration of the poly(lauryl methacrylate)-block-poly(acrylic acid) diblock copolymer in tetrahydrofuran solution is 1-5 mg / mL.

[0016] Preferably, in steps (1a) and (1b), the reaction temperature is 60°C.

[0017] Preferably, in step (1c), the hydrolysis reaction time is 48 hours.

[0018] Preferably, in step (2), the ultrasonic treatment power is 200-400 W and the amplitude is 30%-70%; the mass ratio of gallium indium liquid metal to poly(lauryl methacrylate)-block-poly(acrylic acid) diblock copolymer is 20:1, and the concentration of the poly(lauryl methacrylate)-block-poly(acrylic acid) diblock copolymer in the tetrahydrofuran solution is 2 mg / mL.

[0019] The present invention also provides the application of the above-mentioned polymer brush functionalized liquid metal nano lubricant additive in the preparation of lubricating oil.

[0020] Preferably, the amount of the polymer brush functionalized liquid metal nano lubricant additive added to the lubricating oil is 0.05 wt%-1.0 wt%.

[0021] Compared with the prior art, the present invention has the following beneficial effects: 1. This invention designs and synthesizes a poly(lauryl methacrylate)-block-poly(acrylic acid) diblock copolymer. Utilizing the strong coordination interaction between the carboxyl groups in the poly(acrylic acid) blocks and the gallium oxide layer on the surface of liquid metal nanodroplets, in-situ grafting of the diblock copolymer onto the surface of the liquid metal nanodroplets is achieved, forming a stable polymer brush structure. The poly(lauryl methacrylate) blocks in this polymer brush structure have long alkyl side chains, exhibiting good solubility in base oils and providing excellent steric stabilization for the liquid metal nanodroplets, significantly improving their dispersion stability in base oils. Experimental results show that the polymer brush functionalized liquid metal nanolubricant additive prepared in this invention did not show significant sedimentation after standing in base oil for 3 days, while the unmodified liquid metal nanodroplets showed significant sedimentation within 12 hours.

[0022] 2. This invention achieves effective control over the size of liquid metal nanodroplets by regulating the block composition of the diblock copolymer, particularly the ratio of the degree of polymerization of poly(lauryl methacrylate) blocks to poly(acrylic acid) blocks. When the degree of polymerization ratio is approximately 1:1, nanodroplets with an average particle size of approximately 200 nm and a uniform particle size distribution can be obtained. However, when the degree of polymerization ratio is too high, the steric hindrance effect of the long-chain alkyl groups hinders the effective contact between the carboxyl groups and the droplet surface, resulting in an increase in droplet size to approximately 900 nm. This size control mechanism provides an effective means to optimize the tribological properties of nano-lubricating additives.

[0023] 3. The polymer brush functionalized liquid metal nano-lubricant additive prepared in this invention exhibits excellent friction-reducing and anti-wear properties even at extremely low addition levels (0.1 wt%). Tribological test results show that this additive can completely avoid adhesion on the friction pair surface under a 200 N load, maintaining a low and stable coefficient of friction (approximately 0.116-0.119) throughout the entire test cycle. Compared with the base oil PAO10, the average coefficient of friction is reduced by 47.0%, and the wear volume is reduced by 82.1%-92.8%. Its excellent lubrication performance stems from the formation of a robust chemical reaction film embedded with metal oxide nanocrystals during the friction process. This friction film effectively prevents direct metal-to-metal contact and reduces abrasive wear.

[0024] 4. The preparation method employed in this invention is simple and efficient. Through ultrasound-assisted in-situ grafting, pre-synthesized block copolymers are grafted onto the surface of liquid metal nanodroplets in one step, eliminating the need for complex post-processing steps. This method offers advantages such as mild reaction conditions, simple operation, and ease of large-scale production. Furthermore, by adjusting the composition of the block copolymer and the ultrasonic conditions, precise control over the nanodroplet size can be achieved, exhibiting excellent process adjustability and repeatability. Attached Figure Description

[0025] Figure 1 This is a schematic diagram illustrating the synthesis and structure of the PLMA-b-PAA copolymer of the present invention.

[0026] Figure 2 This is a schematic diagram of the preparation process of the PLMA-b-PAA@EGaIn nanodroplets of the present invention.

[0027] Figure 3 This is a photograph showing the stability of the PLMA-b-PAA@EGaIn nanodroplets of the present invention in PAO10.

[0028] Figure 4 The graph shows the friction-reducing and anti-wear properties of the PLMA-b-PAA@EGaIn additive of this invention, where (a) represents PAO10, PAO-EGaIn, and PLMA at different concentrations. 40-b-PAA 40 (a) The friction coefficient curve of @EGaIn additive; (b) The travel curve of PAO, PAO-EGaIn and PLMA-b-PAA@EGaIn additives as a function of test time; (c) The corresponding average friction coefficient value and wear volume.

[0029] Figure 5 The present invention comprises PAO10, PAO-EGaIn, and PLMA. 40 -b-PAA 40 Characterization images of the wear surface of the @EGaIn additive (0.1 wt%), where (a) is the 3D morphology; (b) is the SEM image; and (c) is the 2D cross-sectional profile image. Detailed Implementation

[0030] The technical solution of the present invention will be clearly and completely described below with reference to the embodiments thereof. It should be noted that this embodiment is based on the present technical solution and provides detailed implementation methods and specific operation processes, but the protection scope of the present invention is not limited to this embodiment.

[0031] Example 1 (1) Synthesis of macromolecular initiator (PLMA-Br) In a Schlenk reaction flask equipped with a magnetic magnet, EBiB (0.05 g, 2.56 × 10⁻⁶ ...) was added sequentially. -4 mol), monomer LMA (7.5 mL, 2.56 × 10⁻⁶) -2 A mixture of CuBr2 and Me6TREN (2.3 mg CuBr2, 1.03 × 10⁻⁶ mol) was prepared. -5 mol; Me6TREN, 11.8 mg, 5.15×10 -5 The reaction system contains 1 mol of [LMA] and 7.5 mL of anisole as solvent. The molar ratio of each component in the reaction system is: [LMA] / [EBiB] / [CuBr2] / [Me6TREN]=100 / 1 / 0.04 / 0.2.

[0032] The reaction flask was sealed and purged with nitrogen for 20 minutes to remove oxygen from the system. Then, 8.3 mg of Sn(EH)2 was dissolved in a small amount of anisole and injected into the reaction system. After degassing, the reaction flask was immediately placed in an oil bath preheated to 60°C to initiate ATRP polymerization. Small samples were periodically taken using a degassing syringe during the reaction. 1 ¹H NMR analysis was used to monitor the reaction process and determine the monomer conversion rate.

[0033] Once the reaction reached the target conversion rate, the reaction system was exposed to air to quench the reaction. Subsequently, the reaction solution was passed through a flash column filled with neutral alumina to remove catalyst residues. The purified reaction solution was added dropwise to ice-cold anhydrous methanol under stirring to precipitate the polymerization product. The product was collected and dried in a vacuum drying oven at 50°C for 48 h to obtain the macromolecular initiator PLMA-Br.

[0034] (2) Synthesis of block copolymer (PLMA-b-PtBA) Following the same experimental procedure as for the synthesis of the macromolecular initiator PLMA-Br, PLMA-Br (0.4 g), tBA (0.5 g), CuBr2 (0.35 mg), Me6TREN (1.8 mg), and anisole (1.5 mL) were added to a Schlenk reaction flask containing a magnetic stir bar. The reaction flask was sealed, and nitrogen gas was bubbled through it for 20 min to remove oxygen from the system. Subsequently, 0.5 mL of pre-degassed Sn(EH)2 stock solution was injected into the reaction system.

[0035] After degassing, the reaction flask was immediately placed in an oil bath preheated to 60°C to initiate ATRP polymerization. During the reaction, small samples were periodically drawn using a degassing syringe. 1 ¹H NMR analysis was used to monitor the reaction progress and determine the monomer conversion. Once the expected conversion was achieved, the reaction system was exposed to air to quench the reaction. Subsequently, the reaction solution was passed through a flash column filled with neutral alumina to remove catalyst residues. The purified reaction solution was added dropwise to ice-cold anhydrous methanol under stirring to precipitate the polymerization product. The product was collected and dried in a vacuum oven at 50°C for 48 h to obtain the block copolymer PLMA-b-PtBA.

[0036] This method was used to synthesize PLMA-b-PtBA copolymers with different block ratios.

[0037] (3) Preparation of block copolymer (PLMA-b-PAA) 0.8 g of PLMA-b-PtBA diblock copolymer was dissolved in a round-bottom flask containing 8 mL of DCM. While the reaction mixture was magnetically stirred, 1.6 mL of TFA was slowly added to the homogeneous solution. The reaction mixture was stirred at room temperature for 48 h to ensure complete hydrolysis of the tert-butyl groups in the PtBA blocks.

[0038] The reaction solution was then added dropwise to ice-cold anhydrous methanol under stirring to allow precipitation and separation. The product was collected and dried in a vacuum drying oven at 50°C for 48 h to remove solvent and residual acid, yielding the block copolymer PLMA-b-PAA. PLMA-b-PAA copolymers with different block ratios were obtained by hydrolysis using this method. The molecular weight data of the obtained copolymers are shown in Table 1.

[0039] Table 1. Molecular weight data of block copolymers with different compositions (4) Preparation of PLMA-b-PAA functionalized EGaIn (PLMA-b-PAA@EGaIn) nanodroplets EGaIn (200 mg) and a THF solution of the block polymer (2 mg / mL, 10 mL) were added to a 20 mL glass vial. The vial was then placed in an ice-water bath and sonicated for 60 min using a probe sonicator (Sonic VCX500, 300W, 50% amplitude). The resulting gray suspension was the block copolymer-functionalized liquid metal nanodroplet, namely PLMA-b-PAA@EGaIn nanodroplets.

[0040] The gray suspension was centrifuged at 10,000 rpm for 20 min, the precipitate was retained, the supernatant was discarded, and the washing was repeated twice to remove free polymer. The obtained PLMA-b-PAA@EGaIn nanodroplet precipitate was collected and then redispersed in the appropriate solvent and lubricating oil according to the required concentration for subsequent characterization.

[0041] Structural characterization and performance evaluation: (1) Effect of PLMA-b-PAA copolymer composition on EGaIn nanodroplet size This embodiment further explores the control of droplet size and distribution through the molecular design of block copolymers. According to the measured data (see Table 2), the ratio of the degree of polymerization of PLMA to PAA (DP...) PLMA / DP PAA It plays a key role in the anchoring interaction at the equilibrium interface and the bridging interaction between adjacent droplets.

[0042] Table 2. Effect of PLMA-b-PAA copolymer composition on EGaIn nanodroplet size Experiments determined that the optimal copolymer composition was PLMA. 40 -b-PAA 40 , its DP PLMA / DP PAA The ratio is approximately 1.0. To verify this hypothesis, we synthesized another material with the same DP.PLMA / DP PA PLMA copolymer with an A ratio of (1.0) 15 -b-PAA 15 It was used to stabilize EGaIn nanodroplets, and the results were consistent with those obtained by PLMA. 40 -b-PAA 40 Copolymer similarity: The average particle size of the prepared nanodroplets was approximately 200 nm, and the PDI was 0.13, confirming the DP... PLMA / DP PAA The ratio plays a dominant role in the size regulation of EGaIn nanodroplets. Meanwhile, when the degree of polymerization of the PAA block is fixed at 15, increasing the degree of polymerization of the PLMA block to 40 and 70 respectively (i.e., PLMA...) 40 -b-PAA 15 and PLMA 70 -b-PAA 15 The resulting nanodroplets showed a sharp increase in average particle size to approximately 900 nm, and the PDI increased to 0.24. This indicates that the PLMA segments are too long (i.e., DP...). PLMA / DP PAA An excessively high DP (displacement ratio) can hinder effective contact between the active carboxyl groups and the droplet surface, thereby reducing interfacial anchoring efficiency and leading to increased droplet size and a wider particle size distribution. It is worth noting that the optimal DP for preparing polymer brush-grafted nanodroplets... PLMA / DP PAA The ratio is expected to vary with the size of the side groups of the stable polymer chain.

[0043] (2) Stability characterization of PLMA-b-PAA@EGaIn nanodroplets The stability of PLMA-b-PAA@EGaIn nanodroplets in polyalphaolefin (PAO) lubricating oil was investigated (e.g., ...). Figure 3 (As shown). Over a wide concentration range, PLMA-b-PAA@EGaIn nanodroplets showed no significant sedimentation after 3 days, exhibiting excellent dispersion stability. In contrast, unmodified EGaIn nanodroplets showed significant sedimentation after 12 hours and were completely precipitated after 3 days.

[0044] (3) Characterization of the friction reduction properties of PLMA-b-PAA@EGaIn additive The functionalized liquid metal nanoparticle suspension was centrifuged at 1000 rpm for 3 min to remove larger nanoparticles. The supernatant was then centrifuged at 4500 rpm for 20 min, the supernatant was discarded, and a small amount of solvent was added to obtain a high-concentration PLMA-b-PAA@EGaIn suspension. This suspension was added to PAO10 at the specified mass ratio, and the mixture was sonicated in an ice-water bath for 5 min to obtain a lubricating oil with a certain concentration of additives.

[0045] Using the SRV-IV fretting friction and wear tester, under steel ball / disc contact conditions, the effects of different concentrations (0.05 wt%, 0.1 wt%, 0.3 wt%, 0.5 wt%, and 1.0 wt%) of PLMA were evaluated. 40 -b-PAA 40 The frictional properties of the @EGaIn additive were tested using pure PAO and PAO containing pure EGaIn droplets with ungrafted polymer brushes (denoted as PAO-EGaIn) as controls.

[0046] Figure 4 (a) Shows PAO, PAO-EGaIn and different concentrations of PLMA 40 -b-PAA 40 The coefficient of friction (COF) curve of @EGaIn additive. The COF curve of pure PAO exhibits dramatic fluctuations and a sharp rise in the initial test phase, indicating oil film rupture and lubrication failure. After a brief period of high COF, a new oil film reforms, causing the COF to stabilize. The average COF over the entire test period is approximately 0.219. When using ungrafted polymer-modified EGaIn droplets as an additive, its COF curve and average COF value (approximately 0.193) are comparable to pure PAO oil. In contrast, over a wider test concentration range (0.05 wt% - 1.0 wt%), PLMA... 40 -b-PAA 40 @EGaIn additives all maintain low and stable COF (approximately 0.116-0.119), exhibiting excellent friction-reducing properties. Furthermore, at the optimal concentration of 0.1 wt%, PLMA... 40 -b-PAA 40 The average COF of @EGaIn was reduced by 47.0% compared to the base oil PAO10.

[0047] Furthermore, during the friction test, the testing machine's stroke was adjusted to fluctuate slightly around a preset value (1 mm). It is noteworthy that the stroke curve exhibits abrupt changes when adhesion occurs; therefore, the stroke curve was used to detect adhesion. Both PAO10 and PAO-EGaIn showed significant adhesion behavior, while PLMA... 40 -b-PAA40 @EGaIn's travel curve remains very smooth. Figure 4 (b) indicates that PLMA 40 -b-PAA 40 @EGaIn did not stick.

[0048] (4) Characterization of the anti-wear properties of PLMA-b-PAA@EGaIn additive The 3D morphology of the wear marks on the surface of the steel block was obtained using a non-contact 3D surface profilometer. Figure 5 ) and corresponding wear volume ( Figure 4 (c) Characterization was performed. The results showed that the wear volume of base oil PAO10 was approximately 48.27 × 10⁻⁶. 4 μm 3 The wear volume of PAO-EGaIn decreased slightly to 42.17 × 10⁻⁶. 4 μm 3 (Reduced by 12.6%). Within the tested concentration range, the wear volume of the PLMA-b-PAA@EGaIn additive decreased sharply to 3.47 × 10⁻⁶. 4 -8.62×10 4 μm 3 Compared to base oil PAO10, it reduced wear volume by 82.1%-92.8%. At the optimal concentration of 0.1 wt%, it showed the highest reduction in wear volume at 92.8%, exhibiting the best wear resistance performance, consistent with the maximum reduction in coefficient of friction (COF).

[0049] Figure 5 (bc) shows the two-dimensional (2D) cross-sectional profile and surface morphology of the wear scars. Among them, the wear scars of PAO10 and PAO-EGaIn are larger, with wear scar widths of 0.82 mm and 0.79 mm, respectively, and corresponding maximum depths of 2.98 μm and 2.28 μm, respectively. Moreover, the surfaces of these wear scars are very rough, with obvious grooves and a large amount of wear debris, indicating that severe adhesive wear and abrasive wear have occurred.

[0050] For the PLMA-b-PAA@EGaIn additive, the wear scars were negligible, with a width of 0.38 mm and a maximum depth of 0.60 μm. The surface was extremely smooth, without obvious grooves or wear debris. The superior anti-wear properties of the PLMA-b-PAA@EGaIn additive, along with its low and stable COF, confirmed the rapid formation of a highly efficient boundary lubrication film in the initial stage of the friction test, indicating that the grafted polymer brush enhanced the wettability and dispersion stability of the EGaIn nanodroplets.

Claims

1. A method for preparing a polymer-functionalized liquid metal nano-lubricant additive for brushes, characterized in that, Includes the following steps: (1) Synthesis of poly(lauryl methacrylate)-block-poly(acrylic acid) block copolymer: (1a) In a Schlenk reaction flask, ethyl α-bromoisobutyrate, lauryl methacrylate, CuBr2, Me6TREN and anisole were added. The reaction flask was sealed, and after nitrogen was bubbled to remove oxygen, Sn(EH)2 was injected. The reaction flask was placed in an oil bath at 50~70℃ for reaction. After the reaction was completed, the mixture was allowed to settle and then dried under vacuum to obtain the macromolecular initiator PLMA-Br. (1b) The PLMA-Br obtained in step (1a), tert-butyl acrylate, CuBr2, Me6TREN and solvent anisole were added to a Schlenk reaction flask, and after nitrogen was purged to remove oxygen, Sn(EH)2 was added. The reaction was carried out in an oil bath at 60°C. After the reaction was completed, the block copolymer PLMA-b-PtBA was obtained by sedimentation and drying. (1c) Dissolve the PLMA-b-PtBA obtained in step (1b) in dichloromethane, add excess trifluoroacetic acid under stirring, and react at room temperature for 24 to 72 hours to completely hydrolyze the tert-butyl groups in the PtBA blocks. After precipitation and drying, the block copolymer PLMA-b-PAA is obtained. (2) Preparation of polymer brush-functionalized liquid metal nanodroplets: The gallium indium liquid metal EGaIn was mixed with the tetrahydrofuran solution of PLMA-b-PAA obtained in step (1c), and ultrasonically treated in an ice-water bath for 30-120 minutes to obtain PLMA-b-PAA-functionalized gallium indium liquid metal nanodroplets, namely the polymer brush-functionalized liquid metal lubricating additive.

2. The preparation method according to claim 1, characterized in that, In step (1a), the molar ratio of lauryl methacrylate, ethyl α-bromoisobutyrate, CuBr2, Me6TREN and Sn(EH)2 is (50~150):1:(0.02~0.06):(0.1~0.3):(0.1~0.3).

3. The preparation method according to claim 1, characterized in that, In step (1b), the molar ratio of tert-butyl acrylate, PLMA-Br, CuBr2, Me6TREN and Sn(EH)2 is (50~150):1:(0.02~0.06):(0.1~0.3):(0.1~0.3).

4. The preparation method according to claim 1, characterized in that, The mass ratio of the gallium indium liquid metal to PLMA-b-PAA in step (2) is (10-30):1, and the concentration of PLMA-b-PAA in the tetrahydrofuran solution of PLMA-b-PAA is 1-5 mg / mL.

5. A polymer brush functionalized liquid metal nano-lubricant additive obtained by the preparation method according to any one of claims 1 to 4, characterized in that, The lubricating additive is EGaIn nanodroplets modified with PLMA-b-PAA block copolymer, wherein the polyacrylic acid blocks in the PLMA-b-PAA block copolymer coordinate with the gallium oxide layer on the surface of the EGaIn nanodroplets through their carboxyl groups to form a polymer brush structure.

6. The polymer brush functionalized liquid metal nano-lubricant additive according to claim 5, characterized in that, In the PLMA-b-PAA block copolymer, the degree of polymerization ratio of polymethyl methacrylate block to polyacrylic acid block is (0.5~2):

1.

7. The polymer brush functionalized liquid metal nano-lubricant additive according to claim 5, characterized in that, The average particle size of the EGaIn nanodroplets is 100 nm to 900 nm.

8. The use of the polymer brush functionalized liquid metal nano-lubricant additive according to any one of claims 5 to 7 in the preparation of lubricating oil.

9. The application according to claim 8, characterized in that, The polymer brush functionalized liquid metal nano lubricant additive is added to the lubricating oil at a rate of 0.05 wt% to 1.0 wt%.

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