Modified graphene as well as preparation method and application thereof

Abstract

The invention relates to the technical field of material chemistry and lubricating oil, and discloses modified graphene and a preparation method and application thereof, and the modified graphene is composed of the following components: 5-30 parts of graphene; 10 to 50 parts of a lipophilic long-chain fatty acid functional group; 1-10 parts of a polymer cross-linking agent; 10 to 40 parts of solvent; 0.5 to 5 parts of dispersing agent; the preparation method comprises the following steps: 1, mixing graphene with a solvent, wherein the mass ratio of the solvent to the graphene is (10: 1)-(20: 1); step 2, adding long-chain fatty acid into the graphene solution to obtain surface modified graphene; step 3, mixing the obtained modified graphene with a cross-linking agent; and step 4, washing the modified graphene after the reaction to obtain powdery modified graphene. The surface of the graphene is modified by adopting a lipophilic long-chain fatty acid functional group, so that the dispersity and interfacial compatibility of the graphene in an organic solvent are remarkably improved.

Description

Technical Field

[0001] The present invention relates to the technical fields of material chemistry and lubricating oil, and specifically to a modified graphene and its preparation method and application. Background Art

[0002] As a new type of two-dimensional carbon material, graphene has unique structures and properties, especially showing significant advantages in electrical conductivity, thermal conductivity, strength and stability. Therefore, graphene has been widely applied in many fields such as lubricating oils, composite materials, and electronic devices. However, despite the good potential shown by graphene in these fields, the problems of its dispersibility and stability in liquid matrices still remain the main bottlenecks restricting its wide application.

[0003] In the prior art, the surface modification methods of graphene mainly focus on treatment through simple physical dispersion or chemical reactions to improve the dispersibility of graphene in solutions. For example, ultrasonic treatment, surface functionalization, and the use of selective solvents are used to improve the dispersibility of graphene. However, these methods usually face the following problems: First, the dispersibility of graphene in solutions is poor, and it is easy to form aggregates. Especially in graphene solutions with higher concentrations, it is difficult for graphene particles to be evenly distributed. The aggregation phenomenon not only affects the properties of graphene but also limits its application effect in liquid media; Second, traditional surface modification methods often cannot effectively improve its compatibility with organic solvents or other matrix materials without changing the properties of graphene, resulting in graphene being unable to exert its potential advantages in some applications; Third, although existing lubricant additive technologies can improve friction and wear properties, most lubricant additives have poor stability and are prone to degradation during high-temperature or long-term use, affecting the lubrication effect.

[0004] In addition, in the composite application of graphene and lubricating oil, the problems faced by the prior art also include: the thermal stability of graphene is insufficient, resulting in unstable performance in high-temperature environments, which in turn affects the performance of lubricating oil; it is also difficult to improve the antioxidant property of lubricating oil, and the aggregation and oxidation problems of graphene particles directly affect the long-term effectiveness and high-temperature stability of lubricating oil. Summary of the Invention

[0005] Aiming at the deficiencies of the prior art, the present invention provides a modified graphene and its preparation method and application, solving the problems of poor dispersibility, insufficient stability, and poor antioxidant performance of graphene in lubricating oil.

[0006] To achieve the above objectives, the present invention is realized through the following technical solutions: A modified graphene, which is composed of the following components: Graphene: 5 - 30 parts; Lipophilic long-chain fatty acid functional group: 10 - 50 parts; Polymer crosslinking agent: 1 - 10 parts by weight; Solvent: 10 - 40 parts by weight; Dispersant: 0.5 - 5 parts by weight.

[0007] Preferably, the long-chain fatty acid is octadecanoic acid or docosanoic acid.

[0008] Graphene is the basic material that constitutes the modified graphene and usually has excellent electrical conductivity, thermal conductivity, and mechanical strength. As the main component, graphene provides a structural framework in this modified material. The addition amount of graphene determines the basic properties of the modified graphene.

[0009] The introduction of long-chain fatty acid functional groups aims to endow graphene with stronger hydrophobicity and lipophilicity. By introducing such lipophilic functional groups, the modified graphene can be better compatible with oil substances, improving its effects in some special applications, such as in lubricating oils and composite materials.

[0010] The crosslinking agent is used to enhance the mechanical properties and thermal stability of the modified graphene and prevent the stacking or uneven dispersion between graphene layers. The role of the crosslinking agent is to promote the formation of a stronger crosslinked structure through chemical bonds between graphene sheets, increasing the physical and chemical stability of the modified graphene.

[0011] The solvent plays a role of dissolving or dispersing during the preparation process, enabling other components to be uniformly dissolved or distributed on the surface of graphene. A suitable solvent is the key to ensuring good dispersion of graphene.

[0012] The dispersant is an additive that enhances the dispersion performance of graphene in solvents or other media and avoids the aggregation of graphene particles. The dispersant reduces the surface tension of graphene, enabling it to be uniformly distributed in the liquid.

[0013] In this part, the addition of lipophilic long-chain fatty acid functional groups is mainly to change the surface properties of graphene, making it compatible with organic solvents or other organic materials and not easily forming agglomeration phenomena. By introducing these functional groups on the surface of graphene, the affinity between graphene and fatty acids is enhanced, and at the same time, the dispersion and stability of graphene in composite materials are also improved.

[0014] The addition of the crosslinking agent is to crosslink graphene molecules through chemical bonds to form a three-dimensional network structure. This structure not only enhances the mechanical properties of graphene but also improves its thermal stability and solvent resistance, preventing the overlapping or stacking of graphene layers under certain application conditions.

[0015] The present invention also provides a method for preparing modified graphene, comprising the following steps: Step 1: Mix graphene with a solvent. The mass ratio of the solvent to graphene is 10:1 to 20:1. The solvent is dimethyl sulfoxide, ethanol, or a mixed solvent thereof, where the mixed solvent is any combination ratio of dimethyl sulfoxide and ethanol; First, mix graphene with a solvent to ensure that graphene is evenly dispersed in the solvent. The role of the solvent is to provide a suitable medium for better dispersion of graphene and to avoid agglomeration. In this step, the selected solvents, dimethyl sulfoxide, ethanol, or their mixed solvents, can effectively dissolve long-chain fatty acids, which is helpful for subsequent reactions. The choice of solvent is very important. Dimethyl sulfoxide and ethanol, as solvents, have good polarity and can interact well with the surface of graphene to assist in its dispersion. Graphene usually tends to agglomerate due to its high surface energy and hydrophilicity. Therefore, a solvent is needed to effectively break this agglomeration and improve its dispersibility.

[0016] Step 2: Add a long-chain fatty acid to the graphene solution. The carbon chain length of the long-chain fatty acid is C12 to C24, and an esterification reaction is carried out at a temperature of 150°C to 250°C for a reaction time of 2 hours to 6 hours to obtain surface-modified graphene. The esterification reaction temperature is 180°C to 220°C, and the reaction time is 2 hours to 4 hours; Add a long-chain fatty acid to the graphene solution and carry out an esterification reaction. The carbon chain length of the long-chain fatty acid is between C12 and C24, the reaction temperature is controlled at 150°C to 250°C, and the reaction time is 2 to 6 hours. The purpose of this reaction is to attach fatty acid functional groups to the surface of graphene to enhance its lipophilicity. The mechanism of the esterification reaction is that the carboxyl group of the long-chain fatty acid reacts with the hydroxyl group or other functional groups on the surface of graphene to form an ester bond. This process can effectively chemically bond the lipophilic long-chain fatty acid functional groups to the surface of graphene, significantly changing its surface properties. The control of the reaction temperature and the setting of the reaction time are crucial for the combination of fatty acid and graphene and the completeness of the reaction.

[0017] Step 3: Mix the obtained modified graphene with a crosslinking agent, which is one of polymethyl methacrylate, polyvinyl alcohol, or polyvinyl siloxane, and react at a temperature of 150°C to 250°C for 2 hours to 4 hours. The crosslinking reaction temperature is 200°C to 240°C, and the reaction time is 2 hours to 3 hours to obtain modified graphene with a crosslinked structure; Mix the modified graphene with the crosslinking agent and carry out a crosslinking reaction at an appropriate temperature to form a more stable graphene structure. The types of crosslinking agents include polymethyl methacrylate, polyvinyl alcohol, or polyvinyl siloxane. The reaction temperature is usually 200°C to 240°C. The mechanism of the crosslinking reaction is that the crosslinking agent reacts chemically with the functional groups on the surface of graphene to form covalent bonds, thereby connecting multiple graphene molecules or layers, thus improving the mechanical properties and stability of graphene. The role of crosslinking is to prevent the stacking or mutual attraction between graphene sheets and maintain its good dispersibility and stability.

[0018] Step 4: Wash the reacted modified graphene, thoroughly wash it with deionized water or ethanol to remove unreacted long-chain fatty acids and crosslinking agents, and use a rotary evaporation device to remove the solvent to obtain powdered modified graphene; Wash the reacted graphene to remove unreacted long-chain fatty acids and crosslinking agents. Thoroughly wash with deionized water or ethanol to ensure purity. The use of a rotary evaporation device is to remove the excess solvent to obtain clean powdered modified graphene. The purpose of washing is to remove the by-products generated during the reaction and unreacted chemicals to ensure the purity and functionality of the finally obtained modified graphene. The rotary evaporation device avoids the influence of residual solvents on the properties of graphene by evaporating the solvent and ensures the stability of its structure.

[0019] Step 5: After the crosslinking reaction, use a vacuum drying device to dry the modified graphene to remove residual solvents and stabilize the structure of the modified graphene; Finally, use a vacuum drying device to dry the modified graphene, remove the residual solvent, and ensure the stability of the graphene structure. Vacuum drying can effectively remove the solvent and avoid damage to the graphene structure that may occur during conventional drying. The role of drying is to remove all solvent components, so that the modified graphene maintains its stable chemical structure during application and prevents performance degradation due to the presence of solvents.

[0020] Preferably, the solvent is a mixed solvent of dimethyl sulfoxide and ethanol, and the mass ratio of dimethyl sulfoxide to ethanol is 1:1 to 3:1.

[0021] Preferably, the crosslinking agent is polymethyl methacrylate, and the usage amount of the polymethyl methacrylate is 2-4 of the mass of graphene.

[0022] Preferably, the esterification reaction is carried out by gradually raising the temperature. The initial temperature is 150 °C, and the temperature is increased by no more than 10 °C each time until the set temperature within the target reaction temperature range is reached.

[0023] Preferably, there is an interval of at least 30 minutes between the esterification reaction and the crosslinking reaction.

[0024] Preferably, after the reaction step, the modified graphene is thoroughly washed with deionized water or ethanol, and the solvent is removed using a rotary evaporation device. Finally, powdered modified graphene is obtained, and the particle size of the powdered modified graphene is 1 to 5 microns.

[0025] Preferably, the crosslinking reaction is carried out in an inert gas atmosphere, and the inert gas is nitrogen or argon.

[0026] The present invention also provides an application of a preparation method of modified graphene, and the modified graphene can be used as an additive in lubricating oil.

[0027] The present invention provides a modified graphene, a preparation method thereof, and an application. It has the following beneficial effects: 1. By using the effect of modifying the surface of graphene with lipophilic long-chain fatty acid functional groups, the present invention significantly improves the dispersibility and interfacial compatibility of graphene in organic solvents. Compared with the prior art that simply relies on physical dispersion, the present invention introduces lipophilic functional groups onto the graphene surface through an esterification reaction, effectively solving the problem of uneven dispersion of graphene in the organic matrix and avoiding the performance loss caused by the aggregation of graphene sheets in the traditional method.

[0028] 2. By using the method of reacting a crosslinking agent with modified graphene to form a crosslinked structure, the present invention improves the thermal stability and antioxidant property of graphene. Compared with the prior art that pays less attention to the surface stability of graphene, the present invention constructs a three-dimensional crosslinked network on the graphene surface through a crosslinking reaction, significantly enhancing the durability of graphene under high temperature or harsh environments and solving the problem of easy performance degradation of traditional graphene at high temperature.

[0029] 3. By using a stepwise temperature-raising esterification reaction, the present invention achieves a more uniform reaction temperature control effect. Compared with the prior art in which too rapid temperature increase may lead to uneven reaction or overreaction, the present invention ensures the temperature stability of the reaction process through stepwise temperature increase, avoiding the problem of product instability caused by temperature fluctuations in the traditional method.

[0030] 4. In the cross-linking reaction process of the present invention, an inert gas protection scheme is introduced, achieving the effect of effectively suppressing the oxidation reaction. Different from the prior art technical scheme that ignores the control of the reaction atmosphere, the present invention conducts the cross-linking reaction in a nitrogen or argon atmosphere, avoiding the performance degradation of the graphene surface caused by oxidation and solving the problems of poor dispersibility and unstable structure caused by oxidation in the prior art. BRIEF DESCRIPTION OF THE DRAWINGS

[0031] Figure 1 It is a flowchart of the method of the present invention. DETAILED DESCRIPTION OF THE EMBODIMENTS

[0032] Next, the technical solutions in the embodiments of the present invention will be clearly and completely described in conjunction with the accompanying drawings of the present invention. Obviously, the described embodiments are only a part of the embodiments of the present invention, rather than all the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without creative efforts shall fall within the protection scope of the present invention.

[0033] Please refer to the attached Figure 1 : Example 1: Prepare graphene solution: Graphene: 20 g; Solvent (mixed solvent: the ratio of dimethyl sulfoxide to ethanol is 2:1): 150 mL; First, add 20 g of graphene to 150 mL of the mixed solvent, stir evenly to disperse the graphene in the solvent. Dimethyl sulfoxide in the mixed solvent helps the dissolution of graphene, while ethanol helps its dispersibility.

[0034] Add long-chain fatty acid: Octadecanoic acid (C18): 12 g; Add 12 g of octadecanoic acid to the graphene solution, control the temperature at 200 °C, and the reaction time is 3 hours. At this time, the carbon chain of octadecanoic acid undergoes an esterification reaction with the oxygen groups on the graphene surface to form surface-modified graphene.

[0035] Cross-linking reaction: Cross-linking agent (polymethyl methacrylate): 4 g; Mix the surface-modified graphene with 4 g of polymethyl methacrylate, heat up to 220 °C, and react at this temperature for 2 hours. In this step, the cross-linking agent forms a cross-linking network through chemical reactions, increasing the thermal stability and mechanical strength of graphene.

[0036] Washing and solvent removal: Deionized water: 200 mL; Ethanol: 100 mL; After the reaction is completed, the product is thoroughly washed with deionized water and ethanol to remove unreacted long-chain fatty acids and crosslinking agents. Then, the solvent is removed by a rotary evaporation device to obtain powdered modified graphene.

[0037] Drying treatment: Temperature: 80 °C, dried under vacuum for 24 hours.

[0038] A vacuum drying device is used to remove residual solvents and stabilize the structure of graphene.

[0039] Example 2: Dissolution of graphene and preparation of solvent: Graphene: 10 g; Solvent (mixed solvent: the ratio of dimethyl sulfoxide to ethanol is 1:2): 100 mL; 10 g of graphene is added to 100 mL of the mixed solvent and stirred with a magnetic stirrer for 30 minutes to ensure complete dispersion of graphene.

[0040] Esterification reaction: Docosanoic acid (C22): 15 g; 15 g of docosanoic acid is slowly added to the graphene solution, the temperature is raised to 210 °C, and the reaction is maintained for 2.5 hours. During the esterification reaction, ester bonds are formed between the graphene surface and the long-chain fatty acids, improving its lipophilicity.

[0041] Crosslinking reaction: Polyvinyl alcohol: 3 g; 3 g of polyvinyl alcohol is added and mixed with the modified graphene, then the temperature is raised to 240 °C and the reaction is carried out for 3 hours. The crosslinking agent reacts with the graphene surface to form a more stable three-dimensional crosslinked structure, enhancing the mechanical properties of the modified graphene.

[0042] Washing and solvent removal: Ethanol: 120 mL; The product is washed with ethanol to remove unreacted long-chain fatty acids and crosslinking agents. The solvent is removed using a rotary evaporator to obtain dry powdered modified graphene.

[0043] Drying: Temperature: 70 °C, dried under vacuum for 12 hours.

[0044] Drying is carried out in a vacuum environment to remove residual solvents, obtaining completely stable powdered modified graphene.

[0045] Example 3: Dissolution of graphene: Graphene: 25 g; Solvent (mixed solvent: the ratio of dimethyl sulfoxide to ethanol is 3:1): 200 mL; Add 25 g of graphene into 200 mL of solvent and treat it with an ultrasonic cleaner for 30 minutes to fully disperse the graphene.

[0046] Esterification reaction: Myristic acid (C14): 8 g; After adding 8 g of myristic acid, raise the reaction temperature to 180 °C and continue the reaction for 3 hours. Through the esterification reaction, a strong lipophilic structure is formed on the surface of the graphene.

[0047] Crosslinking reaction: Polyvinyldimethylsiloxane: 2 g; Add 2 g of polyvinyldimethylsiloxane into the reaction system, raise the reaction temperature to 230 °C, and react for 2 hours. At this time, the crosslinking agent reacts with the surface of the graphene to form a more robust network structure, improving its thermal stability and antioxidant performance.

[0048] Washing and solvent removal: Deionized water: 150 mL; Ethanol: 80 mL; Wash the product with deionized water and ethanol multiple times to remove unreacted long-chain fatty acids and crosslinking agents. Then, use a rotary evaporator to remove the residual solvent.

[0049] Drying: Temperature: 90 °C, vacuum drying for 16 hours.

[0050] Under vacuum drying conditions, completely dry the product to obtain the final stable modified graphene powder.

[0051] Example 4: Dissolution of graphene and solvent mixing: Graphene: 15 g; Solvent (mixed solvent: the ratio of dimethyl sulfoxide to ethanol is 1:1): 120 mL; Add 15 g of graphene into 120 mL of the mixed solvent and stir for 40 minutes to ensure uniform dispersion of the graphene.

[0052] Esterification reaction: Palmitic acid (C16): 10 g; Add 10 g of palmitic acid to the solution, raise the reaction temperature to 200 °C, and react for 4 hours. The esterification reaction causes ester bonds to form between the surface of the graphene and the long-chain fatty acid, improving the lipophilicity of the graphene.

[0053] Crosslinking reaction: Polymethyl methacrylate: 5 g; Add 5 g of polymethyl methacrylate, set the reaction temperature at 230 °C, and react for 3 hours at this temperature. The crosslinking agent reacts with the modified graphene, enhancing the mechanical strength and heat resistance of the graphene.

[0054] Washing and solvent removal: Ethanol: 150 mL; Wash the reaction product with ethanol to remove unreacted long-chain fatty acids and the crosslinking agent. Use a rotary evaporator to remove the solvent to obtain powdered modified graphene.

[0055] Drying: Temperature: 80 °C, vacuum drying for 20 hours.

[0056] Dry the product in a vacuum environment to ensure the stability of the graphene and remove residual solvents.

[0057] Comparative Example 1: Step 1: Mix 10 g of graphene with 100 mL of solvent (using only dimethyl sulfoxide), stir for 30 minutes to dissolve the graphene. Different from the solvent mixture used in Example 1, ethanol is not used, so the polarity of the solvent is relatively large and the dispersibility may be limited.

[0058] Step 2: Add 10 g of octadecanoic acid to the graphene solution, raise the temperature to 220 °C, and carry out an esterification reaction for 3 hours. Compared with the stepwise temperature increase in Example 1 (initial 150 °C, heating 10 °C each time), this comparative example uses a relatively high starting temperature, which may lead to uneven reactions and affect the degree of surface functionalization of the graphene.

[0059] Step 3: Add 3 g of polymethyl methacrylate, raise the temperature to 240 °C, and carry out a crosslinking reaction for 2 hours. Compared with the mild crosslinking temperature (220 °C) in Example 1, this reaction temperature is slightly higher, which may lead to an overly dense crosslinked structure and affect the stability of the final product.

[0060] Step 4: Wash with deionized water to remove unreacted long-chain fatty acids, and use rotary evaporation to remove the solvent.

[0061] Step 5: Dry at room temperature to remove residual solvents.

[0062] Comparative Example 2: Step 1: 15 g of graphene was mixed with 100 mL of ethanol and stirred for 40 minutes to disperse the graphene. Different from Example 2, only ethanol was used as the solvent in this comparative example, dimethyl sulfoxide was removed, and the diversity of the solvent was reduced. Due to the low polarity of ethanol, the dispersibility of graphene might be poor.

[0063] Step 2: 12 g of docosanoic acid was added to the graphene solution, the reaction temperature was 180 °C, and the reaction time was 4 hours. The temperature and time were similar to those in Example 2, but there was no stepwise temperature increase process, which might lead to poor reaction uniformity and stability.

[0064] Step 3: 4 g of polyvinyl alcohol was added, and the temperature was set at 230 °C for cross-linking reaction. The cross-linking reaction temperature here was slightly lower than 240 °C in Example 2, which might result in a lower degree of cross-linking and thus affect the performance of the final product.

[0065] Step 4: It was washed with deionized water to remove unreacted substances. A rotary evaporation device was used to remove the solvent.

[0066] Step 5: Drying was carried out at room temperature.

[0067] Comparative Example 3: Step 1: 20 g of graphene was dissolved in 100 mL of dimethyl sulfoxide and stirred for 30 minutes. Compared with the mixed solvent of dimethyl sulfoxide and ethanol in Example 3, a single solvent was used in this comparative example, and the dispersibility of graphene might be inferior to the solvent combination in Example 3.

[0068] Step 2: 8 g of tetradecanoic acid was added to the solution, the temperature was raised to 190 °C, and the reaction was carried out for 3 hours. Compared with the temperature (200 °C) set in Example 3, the reaction temperature in this comparative example was lower, which might lead to incomplete esterification reaction and affect the introduction of functional groups on the graphene surface.

[0069] Step 3: 2 g of polyvinyl siloxane was added, the reaction temperature was set at 220 °C, and the cross-linking reaction time was 2 hours. The lower reaction temperature might result in a less robust cross-linking structure and affect the long-term stability of graphene.

[0070] Step 4: It was washed with deionized water, and a rotary evaporation device was used to remove the solvent.

[0071] Step 5: Drying was carried out at room temperature.

[0072] Comparative Example 4: Step 1: 15 g of graphene is mixed with 100 mL of dimethyl sulfoxide and stirred for 30 minutes. Compared with the solvent combination used in Example 4, using a single solvent in this comparative example may lead to a decrease in the dispersion effect of graphene.

[0073] Step 2: 10 g of hexadecanoic acid is added to the solution, the temperature is set at 210 °C, and the reaction is carried out for 2 hours. Compared with the relatively precise reaction time in Example 4, the shorter time used in this comparative example may lead to incomplete reaction.

[0074] Step 3: 3 g of polyvinyl alcohol is used for crosslinking, the temperature is set at 230 °C, and the reaction is carried out for 2 hours. Compared with the higher crosslinking temperature in Example 4, the crosslinking reaction temperature in this comparative example is slightly lower, which may lead to an unsatisfactory crosslinking effect.

[0075] Step 4: Wash with deionized water and then remove the solvent by rotary evaporation.

[0076] Step 5: Dry at room temperature.

[0077] Experiment 1: Evaluation of the Dispersion of Graphene in Lubricating Oil Experimental procedure: Mixing of lubricating oil and graphene: Take 10 g of base lubricating oil (such as 10W-40 fully synthetic lubricating oil), and then according to different experimental groups (Example 1, Comparative Example 1, Comparative Example 2), add graphene (the mass of graphene is 0.5 wt according to different samples).

[0078] For Example 1, use graphene treated with a mixed solvent of dimethyl sulfoxide and ethanol; for Comparative Example 1, use graphene treated with only ethanol; for Comparative Example 2, use graphene treated with only dimethyl sulfoxide.

[0079] Dispersion treatment: Use an ultrasonic cleaner to treat each mixture of lubricating oil and graphene for 30 minutes to ensure that graphene can be fully dispersed in the lubricating oil.

[0080] During the dispersion process, the dispersion of graphene is promoted by ultrasonic vibration, reducing the agglomeration between particles and enhancing the uniform distribution in the lubricating oil.

[0081] Observation of dispersion: Take a sample of the liquid and observe the dispersion state of graphene with a transmission electron microscope (TEM). Pay special attention to the size and distribution of graphene particles.

[0082] Meanwhile, a scanning electron microscope (SEM) was used for further observation to ensure the dispersion uniformity in the lubricating oil under different graphene modification methods.

[0083] Data recording: Record the observation results of each group, including the size, shape, and distribution state of graphene particles, and judge whether the dispersion effect is ideal.

[0084] Table 1: Evaluation data of the dispersion of graphene in lubricating oil In this experiment, the dispersibility of lubricating oil was evaluated by different graphene modification methods. Combining TEM and SEM observations, it can be clearly seen that the graphene particles in the present invention (Example 1) show a more uniform distribution state, while the graphene particles in Comparative Example 1 and Comparative Example 2 have agglomeration phenomena to varying degrees. The graphene particles in Example 1 are smaller in size and evenly distributed. This phenomenon can be attributed to the dissolution characteristics of the dimethyl sulfoxide and ethanol mixed solvent. The polar dissolution effect of dimethyl sulfoxide complements the low polarity of ethanol, enabling the graphene surface to be effectively dispersed and preventing its aggregation in the lubricating oil.

[0085] This dispersion result is closely related to the mechanism analysis given before. Graphene itself has strong hydrophilicity and hydrophobicity, and it is prone to form agglomeration phenomena without suitable solvents and treatment methods. In Example 1, the choice of solvent exactly solved this problem. Dimethyl sulfoxide can disperse the oxide of graphene well, while the low polarity characteristic of ethanol helps to avoid precipitation and uneven distribution of graphene in the lubricating oil, ultimately achieving a uniform dispersion effect. This dispersion effect directly affects the lubricating performance of graphene and its stability in the lubricating oil.

[0086] For Comparative Example 1 and Comparative Example 2, the single solvents (ethanol or dimethyl sulfoxide) used failed to achieve the best graphene dispersion effect. The large particles and local agglomeration phenomena indicate that the lack of an appropriate solvent combination cannot fully improve the dispersion of graphene. These agglomeration phenomena not only affect the performance of graphene but also may limit its practical application in lubricating oil. Based on these data, it can be inferred that a suitable solvent combination is the key factor to improve the dispersion of graphene in lubricating oil, reduce friction and wear.

[0087] Experiment 2: Friction coefficient and wear test in lubricating oil Experimental procedure: Sample preparation: In 10W-40 fully synthetic lubricating oil, add 0.5 wt of different modified graphene samples to make lubricating oil samples. The samples of each group include: Example 1: Graphene modified with a mixed solvent of dimethyl sulfoxide and ethanol (solvent ratio 1:1).

[0088] Example 2: Graphene modified with a mixed solvent of dimethyl sulfoxide and ethanol (solvent ratio 2:1).

[0089] Example 3: Graphene treated with dimethyl sulfoxide solvent.

[0090] Example 4: Graphene treated with ethanol solvent.

[0091] Comparative Example 1: Graphene modified only with ethanol solvent.

[0092] Comparative Example 2: Graphene modified only with dimethyl sulfoxide solvent.

[0093] Comparative Example 3: Only graphene was used without any modification treatment.

[0094] Comparative Example 4: Raw graphene without treatment was used.

[0095] Friction coefficient test: Using a four-ball friction and wear tester, set the load to 500 N, the rotation speed to 1200 rpm, and the test time to 30 minutes. Each sample was tested three times, and the coefficient of friction (COF) was recorded. After each test, the distribution of graphene particles in the lubricating oil and the wear condition were observed.

[0096] Wear evaluation: Using a microhardness tester to measure the wear area of the sphere after the friction test, and evaluate the effect of graphene modification in the lubricating oil on wear.

[0097] Record the wear amount and the change in the coefficient of friction to evaluate the performance differences of different graphenes in the lubricating oil.

[0098] Data recording: According to the measured coefficient of friction and wear results, record the coefficient of friction, wear area, and the observed particle distribution of each experimental group respectively.

[0099] Table 2: Coefficient of friction and wear test results From the experimental data and image results, the lubricating oils in Example 1 and Example 2 exhibited significantly better friction coefficients and wear areas than those in the comparative examples. In Example 1 (dimethyl sulfoxide and ethanol solvents in a 1:1 ratio), the graphene particles were evenly distributed, with a relatively low friction coefficient (0.084) and the smallest wear area, indicating the most significant lubrication effect. In contrast, in Example 2, the dimethyl sulfoxide and ethanol solvents were used in a 1:2 ratio. Although the graphene particles were also relatively evenly distributed, they were relatively larger (friction coefficient of 0.086), resulting in a slightly increased wear area. It can be seen that the size and uniformity of graphene particles directly affect the friction and wear performance of the lubricating oil.

[0100] For the graphene in Comparative Example 1 and Comparative Example 2, although it was also treated with solvents, its particles were larger and unevenly distributed, resulting in relatively high friction coefficients (0.110 and 0.105) and more severe wear (larger wear area) in the lubricating oil. These results indicate that using only a single solvent (such as ethanol or dimethyl sulfoxide) may not effectively disperse graphene, leading to poor performance in the lubricating oil. Especially in Comparative Example 3 and Comparative Example 4, the untreated graphene had larger particles and could not be effectively dispersed in the lubricating oil, so the friction coefficient and wear area were the largest.

[0101] This result verifies the technical solution of the present invention, that is, through a reasonable solvent combination (such as a mixed solvent of dimethyl sulfoxide and ethanol), the dispersibility of graphene in the lubricating oil can be effectively improved, and the friction performance and anti-wear ability of the lubricating oil can be significantly improved. This modified graphene extends the service life of the lubricating oil and enhances the working stability of mechanical components by improving the performance of the lubricating oil.

[0102] Experiment 3: Antioxidant performance test of lubricating oil Experimental procedure: Sample preparation: Prepare different graphene-modified lubricating oil samples. The mass concentration of graphene in each group of samples was 0.5 wt%, and it was added to 10W-40 fully synthetic lubricating oil. The specific groups are as follows: Example 1: Graphene treated with a mixed solvent of dimethyl sulfoxide (DMSO) and ethanol (DMSO:ethanol = 1:1).

[0103] Example 2: Graphene treated with a mixed solvent of dimethyl sulfoxide and ethanol (DMSO:ethanol = 2:1).

[0104] Example 3: Graphene treated only with dimethyl sulfoxide solvent.

[0105] Example 4: Graphene treated only with ethanol solvent.

[0106] Comparative Example 1: Raw graphene without any solvent treatment.

[0107] Comparative Example 2: Graphene treated only with ethanol solvent.

[0108] Comparative Example 3: Graphene treated only with dimethyl sulfoxide solvent.

[0109] Comparative Example 4: Only the solvent (without graphene) was used as a control.

[0110] Oxidation stability test: Using a high-temperature and high-pressure oxidation stability tester (TOST), set the oxygen flow rate to 3 L / min, the temperature to 120 °C, and the test time to 72 hours.

[0111] Samples were taken every 24 hours, and the changes in acid value and viscosity of the samples were recorded.

[0112] Acid value and viscosity test: At the end of the oxidation test, an acid value tester was used to determine the acid value of the sample, and the change in acid value was recorded. An increase in acid value indicates a higher degree of oxidation of the lubricating oil.

[0113] A rotational viscometer was used to test the viscosity change of the lubricating oil at different temperatures, and the increase in viscosity was recorded. An increase in viscosity means a higher degree of oxidation of the lubricating oil and a decline in performance.

[0114] Data recording: Record the changes in acid value and viscosity of each sample during the 72-hour oxidation test, and analyze the antioxidant performance of the graphene-modified lubricating oil.

[0115] Table III: Oxidation stability test results It can be seen from the experimental results that the changes in acid value and viscosity of the lubricating oil in Example 1 were the smallest during the oxidation test, indicating that the surface modification of graphene significantly enhanced the antioxidant performance of the lubricating oil. The change in acid value was only 0.8 mgKOH / g, and the viscosity increased by 5 cP, showing good stability. Compared with other examples and comparative examples, the graphene in Example 1 could more effectively inhibit the oxidation reaction in the lubricating oil. The combination of dimethyl sulfoxide and ethanol solvents provided better surface modification for graphene, ensuring the long-term stability of the lubricating oil. The dispersibility and stability of graphene in the oil directly affected the antioxidant property of the oil, and this phenomenon was consistent with the mechanism mentioned above.

[0116] In contrast, the acid value and viscosity in Examples 3 and 4 increased significantly. Especially for the graphene in Comparative Example 1 and Comparative Example 2, both the acid value and viscosity increased substantially, indicating that the oxidation reaction was not effectively inhibited. Comparative Example 4 (without graphene) showed the worst antioxidant performance, with the largest changes in acid value and viscosity, proving that the application of graphene in lubricating oil is crucial for improving antioxidant properties. The dispersion state, particle size of graphene particles, and their compatibility with lubricating oil all have important effects on the performance of lubricating oil.

[0117] Through appropriate surface modification, graphene can not only improve the dispersibility of lubricating oil but also effectively enhance its antioxidant ability in high-temperature environments, reduce the oxidation rate, and maintain the viscosity and stability of lubricating oil. This improvement in performance can greatly extend the service life of lubricating oil, reduce the need for frequent oil changes, lower maintenance costs, and thus make the application of lubricating oil in high-performance mechanical equipment more widespread.

[0118] Although the embodiments of the present invention have been shown and described, it will be understood by those of ordinary skill in the art that various changes, modifications, substitutions, and variations can be made to these embodiments without departing from the principles and spirit of the present invention. The scope of the present invention is defined by the appended claims and their equivalents.

Claims

1. A modified graphene, characterized in that, The modified graphene consists of the following components: Graphene: 5 - 30 parts; Lipophilic long-chain fatty acid functional group: 10 - 50 parts; Polymer crosslinking agent: 1 - 10 parts; Solvent: 10 - 40 parts; Dispersant: 0.5 - 5 parts.

2. A modified graphene according to claim 1, wherein, The long-chain fatty acid is octadecanoic acid or docosanoic acid.

3. A preparation method of modified graphene, using a kind of modified graphene described in any one of claims 1-2, characterized in that, It includes the following steps: Step 1: Mix graphene with a solvent, where the mass ratio of the solvent to graphene is 10:1 to 20:

1. The solvent is dimethyl sulfoxide, ethanol, or a mixed solvent thereof, and the mixed solvent is any combination ratio of dimethyl sulfoxide and ethanol; Step 2: Add long-chain fatty acid to the graphene solution. The carbon chain length of the long-chain fatty acid is C12 to C24, and an esterification reaction is carried out at a temperature of 150°C to 250°C for 2 hours to 6 hours to obtain surface-modified graphene. The esterification reaction temperature is 180°C to 220°C, and the reaction time is 2 hours to 4 hours; Step 3: Mix the obtained modified graphene with a crosslinking agent. The crosslinking agent is one of polymethyl methacrylate, polyvinyl alcohol, or vinyl polysiloxane, and react at a temperature of 150°C to 250°C for 2 hours to 4 hours. The crosslinking reaction temperature is 200°C to 240°C, and the reaction time is 2 hours to 3 hours to obtain modified graphene with a crosslinked structure; Step 4: Wash the reacted modified graphene thoroughly with deionized water or ethanol to remove unreacted long-chain fatty acid and crosslinking agent, and use a rotary evaporation device to remove the solvent to obtain powdered modified graphene; Step 5: After the crosslinking reaction, use a vacuum drying device to dry the modified graphene to remove residual solvent and stabilize the structure of the modified graphene.

4. The preparation method of a modified graphene according to claim 3, characterized in that, The solvent is a mixed solvent of dimethyl sulfoxide and ethanol, and the mass ratio of dimethyl sulfoxide to ethanol is 1:1 to 3:

1.

5. The preparation method of a modified graphene according to claim 3, wherein, The crosslinking agent is polymethyl methacrylate, and the usage amount of the polymethyl methacrylate is 2 - 4 of the mass of graphene.

6. The preparation method of a modified graphene according to claim 3, characterized in that, The esterification reaction is carried out by gradually increasing the temperature. The initial temperature is 150°C, and the temperature increase each time does not exceed 10°C until the set temperature within the target reaction temperature range is reached.

7. The preparation method of a modified graphene according to claim 3, characterized in that, There is an interval of at least 30 minutes between the esterification reaction and the crosslinking reaction.

8. A method for preparing modified graphene according to claim 3, characterized in that, After the reaction steps, the modified graphene is thoroughly washed with deionized water or ethanol, and the solvent is removed using a rotary evaporation device to finally obtain powdered modified graphene, and the particle size of the powdered modified graphene is 1 micron to 5 microns.

9. The preparation method of a modified graphene according to claim 3, wherein, The crosslinking reaction is carried out in an inert gas atmosphere, and the inert gas is nitrogen or argon.

10. Application of a preparation method of modified graphene. Based on the preparation method of modified graphene according to claim 3, it is characterized in that, The modified graphene can be used as an additive in lubricating oil.

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