Method for preparing solid-liquid coupling super-lubricity system from water-based lubricating liquid based on black phosphorus nanosheets

Abstract

The invention discloses a method for preparing a solid-liquid coupling super-lubricity system from water-based lubricating liquid based on black phosphorus nanosheets. The method comprises the following steps: 1, grafting a polyethylene glycol molecular brush to the surface of a friction pair; 2, preparing a water-based lubricating liquid of the black phosphorus nanosheet; and 3, dropwise adding the water-based lubricating liquid obtained in the step 2 to the surface of the friction pair grafted with the polyethylene glycol molecular brush, so as to form the solid-liquid coupling super-smooth system of the polyethylene glycol molecular brush assisted black phosphorus nanosheet. According to the invention, the black phosphorus nanosheet is assisted by the polymer molecular brush to realize super-lubricity under the contact stress of 530MPa under the condition that a friction chemical film is not formed, so that the super-lubricity system of the black phosphorus is greatly enriched.

Description

Technical Field

[0001] The present invention belongs to the technical field of black phosphorus nanosheets, and specifically relates to a method for preparing a solid-liquid coupled superlubricating system with a water-based lubricant based on black phosphorus nanosheets. Background Art

[0002] Polymer brushes are monolayers formed by physical adsorption or chemical grafting of polymers on the surface of materials, and are a type of polymer material with special structures and properties. In the past few decades, people have shown great interest in the lubricating properties of polymer brushes in aqueous media. Using polymer brushes as boundary lubricants can significantly reduce the coefficient of friction (COF) between sliding surfaces, and they are often applied in fields such as surface modification, biosensing, and nanotechnology.

[0003] Black phosphorus is a two-dimensional layered material with many unique properties and chemical structures. Its crystal structure shows similarities to graphene but has a more complex structure. The lattice structure of black phosphorus consists of hexagonal phosphorus atom rings and intersecting phosphorus atom chains, forming a layered structure. This structure endows black phosphorus with anisotropic and tunable properties. Its excellent slip effect and low interlayer shear force have made black phosphorus shine in the field of tribology. Using it as the solid phase of a solid-liquid coupled superlubricating system can bring excellent lubrication effects.

[0004] Although water-based lubricants and superlubrication solutions for black phosphorus nanosheets have been developed (DOI: https: / / doi.org / 10.1016 / B978-0-444-64313-1.00022-3), they all require a relatively long running-in time before reaching the superlubrication state, and black phosphorus nanosheets need to participate in the formation reaction of the tribochemical film.

[0005] In summary, the defect of the existing technology is that it is impossible to achieve the superlubrication state without a tribochemical film. Summary of the Invention

[0006] To overcome the above technical problems, the purpose of the present invention is to provide a water-based lubricant for black phosphorus nanosheets, its preparation method and application. According to current research, the maximum contact stress that the black phosphorus superlubricating system can reach is 1193 MPa. The present invention uses polymer molecular brushes to assist black phosphorus nanosheets to achieve superlubrication without forming a tribochemical film under a contact stress of 500 - 1000 MPa, which greatly enriches the black phosphorus superlubricating system.

[0007] To achieve the above purpose, the technical solution adopted by the present invention is:

[0008] A method for preparing a solid-liquid coupled superlubricating system with a water-based lubricant based on black phosphorus nanosheets, comprising the following steps;

[0009] Step 1: Graft the polyethylene glycol molecular brush onto the surface of the friction pair;

[0010] Step 2: Prepare an aqueous lubricating fluid of black phosphorus nanosheets;

[0011] Step 3: Drop the aqueous lubricating fluid obtained in Step 2 onto the surface of the friction pair grafted with the polyethylene glycol molecular brush, thereby forming a solid-liquid coupling superlubricating system assisted by the polyethylene glycol molecular brush and black phosphorus nanosheets.

[0012] The specific process of Step 1 is as follows:

[0013] S1. Immerse the friction pair in absolute ethanol and ultrasonically clean it for 10 - 30 min at a power of 400 W to remove surface contamination;

[0014] S2. Immerse the friction pair after removing surface contamination in an aqueous solution of polyethylene glycol at 30 - 55 °C for 24 h to allow the surface to be fully grafted with the polyethylene glycol molecular brush;

[0015] S3. Rinse the friction pair with a large amount of clear water to remove the ungrafted molecular brush.

[0016] The molecular weight of the polyethylene glycol described in S2 is (1000 - 2000) g / mol.

[0017] For low molecular weight polymers, their shorter molecular chains will result in poor mechanical properties, while for high molecular weight polymers, it may cause the molecular brush to curl, affecting the consistency of surface functionalization.

[0018] The specific process of Step 2 is as follows:

[0019] Fully mix the black phosphorus nanosheets, sodium chloride, and the aqueous solution of polyethylene glycol in proportion and ultrasonically process them at a power of 400 W to obtain the aqueous lubricating fluid.

[0020] The particle size of the black phosphorus nanosheets is 10 - 100 nm.

[0021] The particle size of the black phosphorus nanosheets plays a crucial role in the friction performance. As the particle size decreases, its surface area will increase, providing a more uniform friction surface, thus reducing the friction coefficient; however, the smaller the particle size, the greater the preparation cost. Therefore, choosing an appropriate particle size range is beneficial to balance the economy of the process and the lubrication effect.

[0022] The mass ratio of the black phosphorus nanosheets : sodium chloride : the aqueous solution of polyethylene glycol is 1 : (30 - 50) : (7000 - 10000).

[0023] For sodium chloride, the sodium ions will increase their ionic radius through the hydration effect. Besides playing the role of a "rolling bearing" between the friction pairs, they will also keep the polyethylene glycol molecular brush highly stable. In addition, polyethylene glycol shows the best lubrication effect in a 0.1 mol / L salt solution. For polyethylene glycol, adding an excessive amount of polymer to the lubricating fluid can, through re-adsorption, supplement the polyethylene glycol molecular brush that has been damaged due to wear during the friction process.

[0024] The molecular weight of the polyethylene glycol is (200 - 1000) g / mol.

[0025] When polyethylene glycol with a relatively small molecular weight is used as a lubricating fluid, it is not easy to form a fluid friction film between the friction pairs and is not suitable for lubrication under high contact stress. When polyethylene glycol with a relatively large molecular weight is used as a lubricating fluid, it will cause an increase in the viscosity of the lubricating fluid, affecting the overall lubrication performance.

[0026] The concentration of the aqueous solution of the polyethylene glycol is (30 - 50) wt%.

[0027] Adding a certain proportion of water to the lubricating fluid can effectively improve the fluidity and cooling property of the lubricating fluid.

[0028] In the solid-liquid coupling superlubrication system assisted by the polyethylene glycol molecular brush in step 3, the friction coefficient dropped below 0.01 around 450 s, and finally the friction coefficient stabilized between 0.007 and 0.011.

[0029] Advantages of the present invention:

[0030] (1) The preparation method of the present invention can uniformly disperse black phosphorus nanosheets and sodium chloride in the aqueous solution of polyethylene glycol through a preparation method of an aqueous lubricating fluid for black phosphorus nanosheets. The good dispersibility will greatly improve the lubrication effect.

[0031] (2) The preparation method of the present invention can graft the polymer molecular brush onto the surface of the friction pair through a modification scheme of the friction pair, greatly enhancing the friction reduction and wear resistance ability of the friction pair. Description of the drawings

[0032] Figure 1 It is a TEM picture of black phosphorus nanosheets, where: (a) is a typical TEM image, and (b) and (c) are corresponding enlarged images.

[0033] Figure 2 It is a characterization diagram of the grafting on the surface of the friction pair. The characterization by optical microscope: (a) un-grafted SiO 2 sheets; (b) grafted SiO 2 sheets; The characterization by scanning electron microscope: (c) un-grafted SiO 2Flakes; (d) Grafted SiO 2 Flakes; Measurement of static contact angle: (e) Ungrafted SiO2 flakes; (f) Grafted SiO2 flakes; Verification of protein adsorption: (g)(h); (i) Fourier transform infrared spectroscopy pictures.

[0034] Figure 3 It is a friction coefficient comparison chart.

[0035] Figure 4 It is a comparison chart of wear scar depth / width between Example 1 and Comparative Example 3. (a)(b) Optical microscope pictures of Example 1 and Comparative Example 3; (c)(d) Wear scar depth / width pictures of Example 1 and Comparative Example 3. Detailed implementation mode

[0036] The present invention will be further described in detail below with reference to the accompanying drawings.

[0037] Example 1

[0038] This example provides a preparation method of a water-based lubricating fluid of black phosphorus nanosheets and its superlubricity scheme, and the steps are as follows:

[0039] (1) Mix the black phosphorus nanosheets, sodium chloride and aqueous solution of polyethylene glycol in a mass ratio of 1:58.5:10000 and ultrasonically treat to make them evenly mixed, and use it as the water-based lubricating fluid;

[0040] (2) Immerse the SiO 2 flakes in the aqueous solution of polyethylene glycol at 55 °C for 24 h to make the surface fully grafted with polyethylene glycol molecular brushes, and then use it as the friction pair.

[0041] The prepared lubricating fluid is tested by a ball-on-disk friction and wear tester, and the friction pair is a Si 3 N 4 ball with a diameter of 6 mm, with the SiO 2 flakes grafted with polymer molecular brushes as the disk bottom, the load is 2 N, the rotation speed is 130 mm / s, and the test time is 1 h. After testing, the aqueous solution of polyethylene glycol of citric acid-modified black phosphorus nanosheets prepared in this example has a friction coefficient stabilized between 0.007 and 0.011 after about 450 s of running-in time, as Figure 4 shown.

[0042] Example 2

[0043] This example provides a preparation method of a water-based lubricating fluid of black phosphorus nanosheets and its superlubricity scheme, and the steps are as follows:

[0044] (1) Mix the black phosphorus nanosheets, sodium chloride, and polyethylene glycol aqueous solution in a mass ratio of 1:117:10000 and ultrasonically treat to make them evenly mixed, and use it as the water-based lubricant;

[0045] (2) Immerse the SiO 2 sheets in the polyethylene glycol aqueous solution at 80 °C for 24 h to allow the surface to be fully grafted with polyethylene glycol molecular brushes, and then use it as the friction pair.

[0046] The prepared lubricant is tested by a ball-on-disk friction and wear tester. The friction pair is a Si 3 N 4 ball with a diameter of 6 mm, and the SiO 2 sheets grafted with polymer molecular brushes are used as the disk bottom. The load is 2 N, the rotation speed is 130 mm / s, and the test time is 1 h. After testing, the polyethylene glycol aqueous solution of the citric acid-modified black phosphorus nanosheets prepared in this example has a friction coefficient stabilized at about 0.04 after about 750 s of running-in time, as Figure 4 shown.

[0047] Comparative Example 1

[0048] This example provides a preparation method of a water-based lubricant of black phosphorus nanosheets and its superlubricity scheme, and the steps are as follows:

[0049] (1) Mix the sodium chloride and polyethylene glycol aqueous solution in a mass ratio of 1:170 and ultrasonically treat to make them evenly mixed, and use it as the water-based lubricant;

[0050] (2) Immerse the SiO 2 sheets in the polyethylene glycol aqueous solution at 55 °C for 24 h to allow the surface to be fully grafted with polyethylene glycol molecular brushes, and then use it as the friction pair.

[0051] The prepared lubricant is tested by a ball-on-disk friction and wear tester. The friction pair is a Si 3 N 4 ball with a diameter of 6 mm, and the SiO 2 sheets grafted with polymer molecular brushes are used as the disk bottom. The load is 2 N, the rotation speed is 130 mm / s, and the test time is 1 h. After testing, the polyethylene glycol aqueous solution of the citric acid-modified black phosphorus nanosheets prepared in this example has a friction coefficient stabilized at about 0.018 after about 100 s of running-in time, as Figure 4 shown.

[0052] Comparative Example 2

[0053] This example provides a preparation method of a water-based lubricant of black phosphorus nanosheets and its superlubricity scheme, and the steps are as follows:

[0054] (1) Mix the black phosphorus nanosheets and the aqueous solution of polyethylene glycol in a mass ratio of 1:10,000 and ultrasonically treat them to make the mixture uniform, and use it as the water-based lubricant;

[0055] (2) Immerse the SiO 2 sheets in the aqueous solution of polyethylene glycol at 55 °C for 24 h to allow the surface to be fully grafted with polyethylene glycol molecular brushes, and then use it as the friction pair.

[0056] The prepared lubricant is tested by a ball-on-disk friction and wear tester. The friction pair is a Si 3 N 4 ball with a diameter of 6 mm, and the SiO 2 sheet grafted with polymer molecular brushes is used as the disk bottom. The load is 2 N, the rotation speed is 130 mm / s, and the test time is 1 h. After testing, the aqueous solution of polyethylene glycol modified with citric acid of black phosphorus nanosheets prepared in this example has a friction coefficient stable between 0.009 and 0.02 after about 1250 s of running-in time, as Figure 4 shown.

[0057] Comparative Example 3

[0058] This example provides a preparation method of a water-based lubricant of black phosphorus nanosheets and its superlubrication scheme, and the steps are as follows:

[0059] (1) Mix the black phosphorus nanosheets, sodium chloride and the aqueous solution of polyethylene glycol in a mass ratio of 1:58.5:10,000 and ultrasonically treat them to make the mixture uniform, and use it as the water-based lubricant;

[0060] (2) Immerse the SiO 2 sheets in anhydrous ethanol at 55 °C for 24 h to make them clean and pollution-free, and then use it as the friction pair.

[0061] The prepared lubricant is tested by a ball-on-disk friction and wear tester. The friction pair is a Si 3 N 4 ball with a diameter of 6 mm, and the original SiO 2 sheets are used as the disk bottom. The load is 2 N, the rotation speed is 130 mm / s, and the test time is 1 h. After testing, the aqueous solution of polyethylene glycol modified with citric acid of black phosphorus nanosheets prepared in this example has a friction coefficient stable between 0.03 and 0.05 after about 1000 s of running-in time, as Figure 4 shown.

[0062] Experimental analysis:

[0063] The lubricant of the example and the polymer molecular brush grafting scheme of the friction pair in this experiment have good prospects for practical application.

[0064] It can be observed from the attached Figure 1 that the size of the black phosphorus nanosheets is in the range of 10 - 100 nm; by comparing the attached Figure 2 (a)(b), it can be found that there are many mottles on the surface of SiO 2 grafted with polyethylene glycol molecular brushes; by comparing the attached Figure 2 (c)(d), it can be found that there are many papillary objects on the surface of SiO 2 grafted with polyethylene glycol molecular brushes; by comparing the attached Figure 2 (e)(f), it can be found that the static contact angle of the surface of SiO 2 grafted with polyethylene glycol molecular brushes and the surface of ungrafted SiO 2 differs by 14.4° before and after; polyethylene glycol is an excellent anti - protein material, by comparing the attached Figure 2 (g)(h), it can be found that a large amount of protein is adsorbed on the surface of ungrafted SiO 2 ; through the attached Figure 2 (i) it can be found that each characteristic peak corresponds to the vibration of various chemical bonds of polyethylene glycol, which indicates that the polyethylene glycol molecular brush has been successfully grafted onto the surface of SiO 2 .

[0065] It can be seen from the attached Figure 3 that only Example 1 achieved the super - slippery state, and in addition, none of the other experiments reached the super - slippery state.

[0066] It can be observed from the attached Figure 4 (a)(b) that the wear scars on the surface of SiO 2 grafted with polyethylene glycol molecular brushes are shallow and sparse compared with the surface of ungrafted SiO 2 ; from the attached Figure 4 (c)(d) it can be observed that both the width and depth of the wear scars on the surface of SiO 2 grafted with polyethylene glycol molecular brushes are much smaller than those on the surface of ungrafted SiO 2 , which indicates that the polyethylene glycol molecular brush has excellent anti - friction and anti - wear capabilities.

[0067] Table 1 is the parameter table of the examples and comparative examples

[0068]

[0069] The above - mentioned is only the preferred specific implementation mode of the present invention, but the protection scope of the present invention is not limited thereto. Any person skilled in the art within the technical scope disclosed by the present invention, according to the technical solution and inventive concept of the present invention, makes equivalent substitutions or changes, and should be covered within the protection scope of the present invention.

Claims

1. A method for preparing a solid-liquid coupled super-lubricating system using a water-based lubricating fluid based on black phosphorus nanosheets, characterized in that: The steps include: Step 1: Grafting polyethylene glycol molecular brushes onto the friction pair surface; Step 2: Prepare a water-based lubricating fluid for black phosphorus nanosheets; Step 3: Use the water-based lubricating liquid obtained in step 2 to drop on the friction pair surface of the grafted polyethylene glycol molecular brush, thereby forming a solid-liquid coupled super-lubricating system of polyethylene glycol molecular brush-assisted black phosphorus nanosheets.

2. The method for preparing a solid-liquid coupled super-lubricating system using a water-based lubricating liquid based on black phosphorus nanosheets according to claim 1, characterized in that: The step 1 is specifically as follows: S1. Soak the friction pair in anhydrous ethanol and perform ultrasonic cleaning at 400W for 10-30min to remove surface contamination; S2, soaking the friction pair after removing surface contamination in an aqueous solution of polyethylene glycol at 30-55° C. to fully graft the polyethylene glycol molecular brush on the surface; S3. Rinse the friction pair with plenty of clean water to remove the ungrafted molecular brushes.

3. The method for preparing a solid-liquid coupled super-lubricating system using a water-based lubricating liquid based on black phosphorus nanosheets according to claim 2, characterized in that: The molecular weight of the polyethylene glycol described in S2 is (1000-2000) g / mol.

4. The method for preparing a solid-liquid coupled super-lubricating system using a water-based lubricating liquid based on black phosphorus nanosheets according to claim 1, characterized in that: The step 2 is specifically as follows: The aqueous solutions of black phosphorus nanosheets, sodium chloride and polyethylene glycol were fully mixed in proportion and ultrasonically treated at a power of 400 W to obtain a water-based lubricating fluid.

5. The method for preparing a solid-liquid coupled super-lubricating system using a water-based lubricating liquid based on black phosphorus nanosheets according to claim 4, characterized in that: The particle size of the black phosphorus nanosheet is 10-100 nm.

6. The method for preparing a solid-liquid coupled super-lubricating system using a water-based lubricating liquid based on black phosphorus nanosheets according to claim 4, characterized in that: The mass ratio of the black phosphorus nanosheets: sodium chloride: polyethylene glycol aqueous solution is 1: (30-50): (7000-10000).

7. The method for preparing a solid-liquid coupled super-lubricating system using a water-based lubricating liquid based on black phosphorus nanosheets according to claim 4, characterized in that: The molecular weight of the polyethylene glycol is (200-1000) g / mol.

8. The method for preparing a solid-liquid coupled super-lubricating system using a water-based lubricating liquid based on black phosphorus nanosheets according to claim 4, characterized in that: The concentration of the polyethylene glycol aqueous solution is (30-50) wt%.

9. The method for preparing a solid-liquid coupled super-lubricating system using a water-based lubricating liquid based on black phosphorus nanosheets according to claim 1, characterized in that: In the step 3, the friction coefficient of the solid-liquid coupled super-lubricating system of the polyethylene glycol molecular brush-assisted black phosphorus nanosheets dropped to below 0.01 in about 450 seconds, and the final friction coefficient was stabilized between 0.007-0.011.

Images