CN114410372B

CN114410372B - Preparation method of temperature-sensitive composite microgel water-based lubricant

Info

Publication number: CN114410372B
Application number: CN202210118901.5A
Authority: CN
Inventors: 胡丽天; 曹文辉; 丁奇; 秦宝锋; 张松伟
Original assignee: Lanzhou Institute of Chemical Physics LICP of CAS
Current assignee: Lanzhou Institute of Chemical Physics LICP of CAS
Priority date: 2022-02-08
Filing date: 2022-02-08
Publication date: 2022-10-25
Anticipated expiration: 2042-02-08
Also published as: CN114410372A

Abstract

The invention discloses a temperature-sensitive composite microgel water-based lubricant, which is prepared by ultrasonically dispersing a PNIPAM temperature-sensitive microgel solution and oxidized multi-walled carbon nanotubes uniformly. According to the invention, the oxidized multi-walled carbon nanotube and the PNIPAM aqueous microgel are combined, so that the respective limitations of the two materials are made up and even eliminated, and the synergistic enhancement of the water lubricating property is realized. The water-based lubricant is uniformly and stably dispersed for a long time, and has different friction coefficients at different temperatures, so that the water-based lubricant has certain working condition adaptability; when the lubricant is used in cooperation with the DLC coating, the lubricant can realize ultra-low friction and can be used as a lubricant for water-lubricated parts such as sealing rings, sliding bearings and the like on which the DLC coating is deposited.

Description

Preparation method of temperature-sensitive composite microgel water-based lubricant

Technical Field

The invention relates to a water-based lubricant, in particular to a preparation method of a temperature-sensitive water-based lubricant, which can be used as a lubricant for water-lubricated parts such as a sealing ring and a sliding bearing deposited with a DLC coating, and belongs to the technical field of composite materials and lubricating materials.

Technical Field

The water lubrication has the characteristics of no pollution, good cooling performance and easy maintenance, and is widely used for lubrication of metal processing and hydraulic transmission. Water lubrication bearings, dynamic seals and other transmission friction pairs of equipment such as various ships, naval vessels, underwater weapons, nuclear power water cooling systems, water turbines and the like all relate to the water lubrication problem. However, water has the disadvantages of low viscosity and difficulty in forming an effective fluid lubricating film, and the like, and thus the range of application is limited to a great extent. The nano additive is one of widely used methods for improving the lubricating performance of a water lubricating system, but the problems of poor dispersion stability and easy agglomeration exist in a nano material in water, and large-size hard particles formed by agglomeration aggravate abrasive wear of a friction pair instead.

The flexible water-based microgel material developed in recent years, such as poly N-isopropylacrylamide (PNIPAM) microgel, not only has excellent dispersion stability in water as an additive, but also can realize dynamic regulation and control of viscosity of a water-based system based on the temperature-sensitive characteristic thereof. The microgel can form a soft boundary lubricating film at a friction interface in the friction process, so that the wear of abrasive particles at the friction interface is effectively avoided while the lubricating performance and the adaptability to multiple working conditions of a system are improved. However, simple hydrogel systems are generally structurally weak and difficult to accommodate for the constant shear during rubbing. Therefore, the development of an environment-friendly water-based lubricating material with excellent lubricating performance and multi-working condition adaptability remains one of the challenges in the current water lubrication research field.

The friction pair is also an important factor influencing the lubricating performance of a water lubricating system, and the physicochemical characteristics of the surface of the friction pair have important influence on the water lubricating behavior because the thickness of the water lubricating film is far smaller than that of the lubricating oil film. Therefore, the technique of film/coating modification of the surface of the friction pair has gradually become an important method for enhancing the water lubricating performance thereof, wherein the carbon-based solid lubricating film comprises: DLC, GLC, si-DLC, ti-DLC and the like are solid lubricating materials with excellent tribological properties in water environment, and a carbon-based solid lubricating coating deposited on the surface of a water lubricating friction pair ensures that a friction interface has reliable lubrication guarantee under boundary lubrication such as low-speed and frequent start and stop and near-dry friction, thereby meeting the high-reliability requirement of water lubricating machinery. However, the carbon-based solid lubricating coating has a limited service life, and due to the chemical inertia of the carbon-based solid lubricating coating, the carbon-based solid lubricating coating has insufficient responsiveness to the traditional water lubricating additive, so that the friction reduction and the service life extension of the system are difficult to realize through the synergistic lubrication design of the coating and the additive.

In recent years, carbon Nanotubes (CNTs) have been found to have a better synergistic lubricating effect with carbon-based solid lubricating coatings. The carbon nano tube is a hollow cylindrical body formed by winding carbon atoms arranged in an axial honeycomb manner, and has excellent corrosion resistance, high temperature resistance and lubricating effect due to the special space structure. At a friction contact interface, the carbon nano tube mainly changes sliding friction into rolling friction based on a nano mechanical bearing mechanism, so that the friction reduction and wear resistance effects of chemical inert friction pairs such as carbon-based films and the like are realized. However, carbon nanotubes as a lubricant additive require chemical modification of its surface to improve dispersion in a fluid lubricating medium. CN201710497266.5 discloses a technical scheme for using acidified carbon nanotubes as a lubricating oil additive, but the scheme mainly solves the problem of dispersion stability of the carbon nanotubes in oil, and dynamic regulation and control of the viscosity of a lubricating medium cannot be realized. Therefore, at present, for water-lubricated friction pairs, especially friction pairs plated with carbon-based solid lubricating coatings, there is no water-lubricated technical scheme which can realize high stable dispersion of carbon nanotubes and has viscosity dynamic regulation and control performance.

Disclosure of Invention

The invention aims to provide a temperature-sensitive composite microgel water-based lubricant and a preparation method thereof, aiming at solving the problems of the application of the water-based lubricant in the prior art.

The invention relates to a temperature-sensitive composite microgel water-based lubricant, which is prepared by adding multi-walled carbon nanotubes (MWCNTs) into poly N-isopropylacrylamide (PNIPAM) microgel aqueous solution and carrying out ultrasonic homogenization treatment.

The MWCNTS of the multi-wall carbon nano tube has the outer diameter of 20 to 30nm and the length of 10 to 30 mu m. Too small or too large a size is not beneficial to the preparation of the subsequent composite material.

In order to improve the dispersion stability of carbon nanotubes, oxidized multiwall carbon nanotubes (MWCNTs) can be used. The oxidation process of the multi-wall carbon nano tube comprises the following steps: dispersing the multi-walled carbon nano-tube in a mixed acid solution of concentrated nitric acid and concentrated sulfuric acid, heating to 60-80 ℃, and stirring for 8-10 h; repeatedly washing with pure water until pH =7, centrifuging, drying, and grinding to obtain oxidized multi-walled carbon nanotube black powder. In the mixed acid solution, the mass concentration of the concentrated nitric acid is 65%, the mass concentration of the concentrated sulfuric acid is 98%, and the volume ratio of the concentrated nitric acid to the concentrated sulfuric acid is 1:3; the centrifugal rotating speed is 8000 to 12000 rpm/min; the drying temperature is about 50 to 80 ℃.

Preparing the poly N-isopropylacrylamide microgel solution: under the protection of nitrogen (protection for preventing oxidation in the polymerization process), heating and dissolving isopropyl acrylamide (NIPAM) and N, N-Methylene Bisacrylamide (MBA) in water, heating to 60-70 ℃, then adding Ammonium Persulfate (APS) into the reaction system, and carrying out polymerization reaction for 6-8h; and obtaining the poly N-isopropyl acrylamide microgel solution after the reaction is finished. Wherein the molar ratio of the N-isopropylacrylamide to the N, N-methylenebisacrylamide is 1; the molar ratio of the N-isopropylacrylamide to the ammonium persulfate is 1.

In the thermo-sensitive composite microgel water-based lubricant, the mass percent of the oxidized multi-walled carbon nano tube is 0.04-0.12%, and the mass percent of the poly N-isopropylacrylamide microgel is 1.5-1.9%.

The ultrasonic frequency of the ultrasonic homogenization treatment is more than or equal to 40KHz, the power is 500 to 600W, and the ultrasonic time is 20 to 30 min.

Fig. 1 is an appearance picture of the thermo-sensitive composite microgel water-based lubricant prepared by the invention: the composite microgel solution is black, has no obvious impurities, and is uniformly and stably dispersed for a long time.

FIG. 2 shows the transmission electron microscopic morphology of the thermo-sensitive composite microgel water-based lubricant. The microgel is spherical particles in aqueous solution, the modified carbon nano tubes are adsorbed on the surfaces of the microgel particles, and the microgel and the carbon nano tubes mutually promote the dispersibility of the microgel and the carbon nano tubes in water.

FIG. 3 is a graph showing the temperature response characteristics of the temperature-sensitive composite microgel water-based lubricant. It can be seen that in the heating process, the viscosity of the composite microgel water-based lubricant gradually increases with the temperature rise, in the cooling process, the viscosity of the system gradually decreases with the temperature decrease, and the sudden increase point at about 34 ℃ is the critical dissolution temperature of the microgel system, namely, above the temperature, the microgel particles lose water, and below the temperature, the microgel particles absorb water, which also shows the temperature-sensitive characteristic of the water-based lubricant, and as a lubricating medium, the water-based lubricant has certain temperature working condition adaptability.

FIG. 4 is an infrared spectrum of 3390cm of the thermo-sensitive composite microgel water-based lubricant ^-1 Is the characteristic peak of the N-H bond, 1385 cm ^-1 And 1367cm ^-1 Is a characteristic peak of isopropyl in PNIPAM, 3442cm ^-1 Is a characteristic peak at-OH, 1120cm ^-1 The peak is a characteristic peak of-COOH, which shows that the compound contains the characteristic peaks of the oxidized carbon nano-tube and the PNIPAM microgel, namely the substance is successfully synthesized.

2. Lubricating property of thermo-sensitive composite microgel water-based lubricant

The HT-1000 high-temperature reciprocating friction and wear testing machine is adopted, and the specific experimental conditions are as follows: a load of 5N, a frequency of 2Hz, a temperature of 25 ℃ and a temperature of 35 ℃ respectively, and an upper sample of Si with a diameter of 6mm ₃ N ₄ And (3) ceramic balls. Under the condition of pure water lubrication, the lower samples are respectively 304 stainless steel and Si ₃ N ₄ A ceramic block. Under the condition that the water-based lubricant is lubricated (the temperature-sensitive composite microgel water-based lubricant prepared in example 1), the lower sample is a stainless steel block plated with a 2-micron pure DLC film, the hardness of the lower sample is about 15GPa, the Young modulus of the lower sample is about 175 GPa, and the test duration is 30 min.

FIG. 5a is a graph of the coefficient of friction under pure water lubrication conditions. It can be seen that in Si ₃ N ₄ -Si ₃ N ₄ The friction coefficient at 25 ℃ is about 0.65 and the friction coefficient at 35 ℃ is about 0.7 under the condition of a friction pair.

FIG. 5b is a plot of coefficient of friction under water-based lubricant lubrication conditions. In Si ₃ N ₄ Stainless steel has a coefficient of friction of about 0.43 at 25 ℃ and of about 0.4 at 35 ℃ in the case of a friction pair. When the water-based lubricant and the hydrogen-free DLC coating are used together, the friction coefficient is reduced by about 50 percent compared with a DLC friction pair lubricated by pure water, the friction coefficient is reduced by about 90 percent compared with a water-lubricated stainless steel friction pair, and the friction coefficient is reduced by about 90 percent compared with water-lubricated Si ₃ N ₄ The friction coefficient of the friction pair is reduced by about 92%. The oxidized MWCNTs-PNIPAM microgel water machine lubricant prepared by the invention can realize ultra-low friction when being used with a DLC coating in a synergistic way, and mainly benefits from the synergistic effect of the PNIPAM microgel particles and the carbon nano tube MWCNTsAnd the rolling, film forming and other synergistic lubrication mechanisms on the DLC friction interface can realize the ultra-low friction coefficient below 0.03.

In conclusion, the water-based lubricant prepared by ultrasonically compounding the poly N-isopropylacrylamide temperature-sensitive microgel solution and the carbon nano tube is based on the temperature responsiveness of the microgel, so that the problem of insufficient forming capability of a water-lubricated film after the temperature is increased is solved; the bearing capacity of the flexible microgel is enhanced through the carbon nano material, the boundary lubricating performance of the water-based lubricant is improved, and meanwhile, the problem of sedimentation of the carbon nano tube is effectively solved by means of high dispersibility of the microgel in water. The carbon nano tube is combined with the PNIPAM aqueous microgel, so that the respective limitations of the two materials are made up and even eliminated, and the synergistic enhancement of the water lubricating performance is realized. The water-based lubricant is applied to a DLC friction pair, can obviously reduce the friction coefficient of a system, reduces the friction coefficient by about 90 percent compared with a simple water lubrication condition, and can be used as a lubricant for water lubrication parts such as a sealing ring, a sliding bearing and the like deposited with a DLC coating.

Drawings

FIG. 1 is a picture of the appearance of the thermo-sensitive composite microgel water-based lubricant prepared in the present invention.

FIG. 2 shows the transmission electron microscopic morphology of the thermo-sensitive composite microgel.

FIG. 3 is a graph showing temperature response characteristics of the temperature-sensitive composite microgel.

FIG. 4 is an infrared spectrum of the thermo-sensitive composite microgel.

FIG. 5 is a graph of coefficient of friction under water lubrication conditions.

FIG. 6 is a friction coefficient curve of the temperature-sensitive composite microgel.

Detailed Description

Example 1

2g of MWCNTs (20 nm in outside diameter, 15 μm in length) was added to 150 ml mixed acid (65% HNO) ₃ And 98% of H ₂ SO ₄ 1:3), heating the system to 60 ℃, heating, stirring, condensing, refluxing to 8h, cooling to room temperature after the reaction is finished, repeatedly washing the carbon oxide nano tube by ultrapure water after filtering until the pH is =7, and pouring the mixed solution after the last washing until the pH is =7Centrifuging in a centrifuge tube at 8500 r/min for 15 min to obtain precipitate, drying in a 60 deg.C oven for 12 h, taking out, and slightly grinding to obtain black powdered carbon oxide nanotube;

putting 1.55g of NIPAM and 0.03g of MBA into a three-neck flask, adding 120ml of distilled water, magnetically stirring at 50 ℃ until the solution is clear and transparent, introducing high-purity nitrogen (to remove oxygen dissolved in water) into the system for 20 min, raising the reaction temperature to 70 ℃, adding 0.13 g APS into the system, heating, stirring, condensing and refluxing 6 h, and cooling to room temperature to obtain PNIPAM microgel solution;

0.01g of oxidized multi-walled carbon nano tube is added into 25 ml of the PNIPAM microgel solution prepared by the method, and ultrasonic treatment is carried out for 20 min by using an ultrasonic machine with 40KHz and the power of 500W, so as to obtain a uniformly dispersed composite microgel system, namely the temperature-sensitive water-based lubricant, wherein the content of the carbon nano tube is 0.04%, and the content of the PNIPAM microgel is 1.4%.

The HT-1000 high-temperature reciprocating friction and wear testing machine is adopted, and the specific experimental conditions are as follows: a load of 5N, a frequency of 2Hz, a temperature of 25 ℃ and a temperature of 35 ℃ respectively, and an upper sample of Si with a diameter of 6mm ₃ N ₄ Ceramic balls; the lower sample was a stainless steel block plated with a 2 μm pure DLC film, and had a hardness of about 15GPa, a Young's modulus of about 175 GPa, and a test duration of 30 min. The coefficient of friction was tested under the condition that the temperature sensitive water-based lubricating medium was used as a lubricant. The results show an average coefficient of friction of 0.05 at 25 ℃ and 0.024 at 35 ℃ as shown in FIG. 6 a.

Example 2

2.5g of MWCNTs (25 nm in outside diameter, 15 μm in length) was added to 150 ml mixed acid (65% HNO) ₃ And 98% of H ₂ SO ₄ 1:3), magnetically stirring for 10 min, heating the system to 80 ℃, heating, stirring, condensing, refluxing for 9h, cooling to room temperature after the reaction is finished, repeatedly washing with ultrapure water after filtering until the pH is =7, pouring the mixed solution after the last washing into a centrifuge tube, centrifuging for 10 min at the rotating speed of 11000 r/min, putting the obtained precipitate into an oven at 80 ℃, drying for 10h, taking out, slightly grinding to obtain black powdery oxidized polysaccharideA wall carbon nanotube;

putting 1.7 g of NIPAM and 0.05g of MBA into a three-neck flask, adding 150 ml distilled water, magnetically stirring at 50 ℃ until the solution is clear and transparent, introducing high-purity nitrogen into the system to remove oxygen dissolved in the water, raising the reaction temperature to 70 ℃ after 20 min, adding 0.1 g APS into the system, heating, stirring, condensing and refluxing 7 h, and cooling to room temperature to obtain PNIPAM microgel solution;

and adding 0.02g of OH-MWCNTs into 25 ml of PNIPAM microgel solution, and carrying out ultrasonic treatment for 20 min by using a 40KHz ultrasonic machine with the power of 550W to obtain a uniformly dispersed composite microgel system, namely the temperature-sensitive water-based lubricant. Wherein the content of the carbon nano tube is 0.08 percent, and the content of the gel is 1.2 percent.

The coefficient of friction was measured under the condition that the temperature-sensitive water-based lubricating medium was used as a lubricant (the test conditions were the same as above). The results show that the average coefficient of friction was 0.04 at 25 ℃ and 0.03 at 35 ℃ as shown in FIG. 6 b.

Example 3

Taking 1.8g MWCNTs (20 nm in outer diameter, 20 μm in length), adding 150 ml mixed acid (65% ₃ And 98% of H ₂ SO ₄ 1:3), heating the system to 70 ℃, heating, stirring, condensing, refluxing for 10h, cooling to room temperature after the reaction is finished, filtering, repeatedly washing the filtered oxidized carbon nanotube with ultrapure water until the pH is =7, pouring the mixed solution after the last washing into a centrifuge tube, centrifuging for 20 min at the rotating speed of 9000 r/min, putting the obtained precipitate into a 70 ℃ oven, drying for 12 h, taking out, and slightly grinding to obtain black powdery oxidized carbon nanotube, namely oxidized multi-walled carbon nanotube;

putting 1.64g of NIPAM and 0.02g of MBA into a three-neck flask, adding 100 ml distilled water, magnetically stirring at 50 ℃ until the solution is clear and transparent, introducing high-purity nitrogen into the system to remove oxygen dissolved in the water, raising the reaction temperature to 70 ℃ after 20 min, adding 0.15 g of APS into the system, heating, stirring, condensing and refluxing 8h, and cooling to room temperature to obtain PNIPAM microgel solution;

and adding 0.03g of OH-MWCNTs into 25 ml of PNIPAM microgel solution, and carrying out ultrasonic treatment for 25 min by using a 40KHz ultrasonic machine with the power of 450W to obtain a uniformly dispersed composite microgel system, namely the temperature-sensitive water-based lubricant. Wherein the content of the carbon nano tube is 0.12 percent, and the content of the gel is 1.8 percent.

The coefficient of friction was measured under the condition that the temperature-sensitive water-based lubricating medium was used as a lubricant (the test conditions were the same as above). The results show an average coefficient of friction of 0.038 measured at 25 ℃ and 0.028 measured at 35 ℃, the coefficient of friction curves being shown in figure 6 c.

Claims

1. The application of the temperature-sensitive composite microgel water-based lubricant and the DLC coating in synergistic use is characterized in that: the preparation method of the temperature-sensitive composite microgel water-based lubricant comprises the steps of adding a multi-walled carbon nanotube into a poly N-isopropylacrylamide microgel aqueous solution, and carrying out ultrasonic homogenization treatment to obtain the temperature-sensitive composite microgel water-based lubricant;

the multi-walled carbon nanotube is an oxidized multi-walled carbon nanotube, and the oxidation process comprises the following steps: dispersing the multi-walled carbon nano-tube in a mixed acid solution of concentrated nitric acid and concentrated sulfuric acid, heating to 60-80 ℃, and stirring for 8-10 h; repeatedly washing with pure water until pH =7, centrifuging, drying, and grinding to obtain black powder of oxidized multi-walled carbon nanotubes;

preparing the poly N-isopropylacrylamide microgel solution: under the protection of nitrogen, heating and dissolving N-isopropylacrylamide and N, N-methylenebisacrylamide in water, heating to 60-70 ℃, then adding ammonium persulfate into a reaction system, and carrying out polymerization reaction for 6-8h; after the reaction is finished, poly N-isopropyl acrylamide microgel solution is obtained;

in the thermo-sensitive composite microgel water-based lubricant, the mass percent of the multi-wall carbon nano tube is 0.04 to 0.12 percent, and the mass percent of the poly N-isopropylacrylamide microgel is 1.5 to 1.9 percent.

2. The use of the thermo-sensitive composite microgel water-based lubricant in combination with a DLC coating according to claim 1, wherein: the MWCNTs of the multi-wall carbon nano tube have the outer diameter of 20 to 30nm and the length of 10 to 30 mu m.

3. The use of the thermo-sensitive composite microgel water-based lubricant in combination with a DLC coating according to claim 1, wherein: in the mixed acid solution, the mass concentration of the concentrated nitric acid is 65%, the mass concentration of the concentrated sulfuric acid is 98%, and the volume ratio of the concentrated nitric acid to the concentrated sulfuric acid is 1:3.

4. The use of the thermo-sensitive composite microgel water-based lubricant in combination with a DLC coating according to claim 1, wherein: the centrifugal speed is 8000 to 12000 rpm/min.

5. The use of the thermo-sensitive composite microgel water-based lubricant in combination with a DLC coating according to claim 1, wherein: the molar ratio of N-isopropylacrylamide to N, N-methylenebisacrylamide is 1.

6. The use of the thermo-sensitive composite microgel water-based lubricant in combination with a DLC coating according to claim 1, wherein: the molar ratio of the N-isopropylacrylamide to the ammonium persulfate is 1.

7. The use of the thermo-sensitive composite microgel water-based lubricant in combination with a DLC coating according to claim 1, wherein: the ultrasonic frequency of the ultrasonic homogenization treatment is more than or equal to 40KHz, the power is 500 to 600W, and the ultrasonic time is 20 to 30 min.