Oil-dispersible polydopamine nano-lubricating additive and preparation method and application thereof

Abstract

The present invention provides an oil-dispersible polydopamine nano-lubricating additive and a preparation method and application thereof, belonging to the field of new material technology. The additive is prepared by the following method: taking polydopamine nanoparticles, dispersing them in water, adjusting the pH of the dispersion to 3-4 with dilute hydrochloric acid, and continuously stirring the reaction; adding ethyl acetate to the dispersion after the reaction, then dripping a lipophilic fluorine-containing anion salt solution, and stirring for 0.5-1h; obtaining the oil phase after the reaction, and removing the ethyl acetate. The present invention adopts a simple and controllable protonation reaction and anion transfer process to successfully adjust the lipophilicity and lipophobicity of polydopamine nanoparticles, and achieves its long-term dispersion stability in polyethylene glycol base oil for more than 30 days. The polydopamine nanoparticles prepared by the present invention can be directly dispersed in polyethylene glycol lubricating base oil, and have an effective lubricating effect on the friction and wear between metal / metal friction pairs.

Description

Technical Field

[0001] The present invention relates to the technical field of new materials, in particular to an oil-dispersible polydopamine nanoparticle, a preparation method of the oil-dispersible polydopamine nanoparticle and application of the oil-dispersible polydopamine nanoparticle in lubricating oil additives. Background Art

[0002] Polyethylene glycol is a common synthetic base oil, often used as a lubricant for metal processing or mechanical parts. Compared with ordinary mineral oil, polyethylene glycol has many advantages such as environmental protection and biodegradability. However, when pure base oil is used as a single lubricant, it is difficult to achieve a stable and reliable lubrication effect during mechanical operation.

[0003] Organic polymer nanoparticles have excellent physical and chemical properties and good adsorption capacity at the friction interface. At the same time, as soft nanoparticles, they are easily pressed into a film by external force after entering the friction interface, thereby avoiding direct contact with the friction interface. Inspired by mussels, their adhesive proteins rich in amino and catechol groups enable them to adhere to almost any substrate surface. Dopamine has a molecular structure similar to that of adhesive proteins and can be easily self-oxidized and polymerized into polydopamine in an alkaline environment. Polydopamine has excellent adhesion ability like adhesive proteins.

[0004] Although polydopamine can be well dispersed in water-based lubricants, it is difficult to disperse in base oil, which greatly limits its application as an oil-based lubricant additive. Solving the problem of the dispersibility of polydopamine nanoparticles in oil will greatly promote the exploration and application of polydopamine nanoparticles as oil-based lubricant additives. Summary of the invention

[0005] In order to solve at least one of the above problems, the present invention provides a method for preparing an oil-dispersible polydopamine nano-lubricating additive, and the oil-dispersible polydopamine nano-particles are obtained by simply modifying the polydopamine nano-particles.

[0006] Another object of the present invention is to provide an oil-dispersible polydopamine nanoparticle having good oil dispersibility.

[0007] Another object of the present invention is to provide an application of oil-dispersible polydopamine nanoparticles, which can be added to lubricating oil as an additive to improve the lubricating performance of the lubricating oil.

[0008] To achieve the above objectives, the technical solution of the present invention is as follows: a method for preparing an oil-dispersible polydopamine nano-lubricating additive, comprising the following steps;

[0009] S1. Take polydopamine nanoparticles, disperse them in water, adjust the pH of the dispersion to 3-4 with dilute hydrochloric acid at 25-30° C., and continue stirring for 1-2 hours to obtain a dispersion, wherein every 100-200 mg of polydopamine nanoparticles corresponds to 20-30 ml of water;

[0010] S2, adding ethyl acetate to the dispersion after the reaction in S1, and then dropping a lipophilic fluorinated anion salt solution, and stirring for 0.5 to 1 hour, wherein every 20 to 30 ml of water corresponds to 20 to 30 ml of ethyl acetate, and the mass ratio of the lipophilic fluorinated anion salt to the polydopamine nanoparticles is 1.1 to 2.8:1;

[0011] S3, obtain the oil phase of S2 and remove ethyl acetate.

[0012] Specifically, dilute hydrochloric acid is added to the polydopamine dispersion, the main purpose of which is to protonate the surface of the polydopamine nanoparticles. For the protonation process, dilute hydrochloric acid should be used, which can not only provide hydrogen ions for protonation of the polydopamine nanoparticles, but also provide chloride ions. At the same time, the concentration of dilute hydrochloric acid should not be too high. When its concentration is too high, it will destroy the spherical structure of the polydopamine nanoparticles; but it should not be too low. When the concentration is too low, it is difficult to achieve the purpose of protonation. Therefore, after a large number of experiments by the inventors, it was found that when the concentration of dilute hydrochloric acid is in the range of 0.05 to 0.2 mol / L, it has a better effect, preferably 0.1 mol / L.

[0013] When the pH of the dispersion is between 3 and 4, the amino groups on the surface of the polydopamine nanoparticles will be protonated by hydrogen ions. After protonation, the hydrogen ions will adsorb chloride ions, which is the key to subsequent modification.

[0014] After adding ethyl acetate, an oil-water phase is formed, and the lipophilic fluorine-containing anion salt added has a fluorine-containing anion group that is a lipophilic group. At the same time, the chloride ion will quickly exchange ions with the fluorine-containing anion. After the hydrophobic fluorine-containing anion is exchanged to the surface of the polydopamine nanoparticle, it will quickly precipitate from the water. The precipitate enters and dissolves in the upper oil phase during the stirring process. The color of the lower water phase gradually fades to clear, and the color of the upper oil phase gradually darkens, thereby completing the lipophilic modification of the surface of the polydopamine nanoparticle. The fluorine-containing anion salt is one of lithium bistrifluoromethanesulfonyl imide, potassium hexafluorophosphate and sodium tetrafluoroborate.

[0015] Finally, the solvent (ethyl acetate) in the oil phase is removed to obtain oil-dispersible polydopamine nanoparticles. When removing the solvent, low temperature is used, usually at 20 to 40°C. Removing the solvent under this condition will not affect the performance of the oil-dispersible polydopamine nanoparticles. Theoretically, the existing common low-temperature solvent removal methods can be used, such as natural evaporation, rotary evaporation, and reduced pressure distillation. However, in terms of actual results, the efficiency of removing ethyl acetate by natural evaporation is low and the time is long; the oil-dispersible polydopamine nanoparticles obtained by rotary evaporation and reduced pressure distillation are difficult to collect; after a large number of experiments by the inventor, it was found that when the solvent is removed under ventilation conditions, the time is relatively short, and the obtained oil-dispersible polydopamine nanoparticles are easy to collect, and the temperature is preferably 25 to 30°C.

[0016] One embodiment of the present invention is that the preparation method of the polydopamine nanoparticles is as follows: dissolving dopamine hydrochloride in water, wherein the amount of dopamine hydrochloride added is 0.5g to 1.0g for every 10ml of water; taking water, ethanol and ammonia water in a volume ratio of 90:40:0.5 to 3.5, stirring for 30min at 30°C to obtain a mixed solution; mixing the dopamine hydrochloride solution and the mixed solution, and continuously stirring for 3 to 24h under light-proof conditions; and centrifuging and washing the product after the reaction to obtain a mixed solution.

[0017] Specifically, in the dopamine hydrochloride solution, if the amount of dopamine hydrochloride is too much, the polydopamine nanoparticles formed will agglomerate and grow during the reaction, resulting in the polydopamine nanoparticles finally obtained being difficult to meet the actual use requirements; if the amount is too little, it is difficult to obtain formed nanoparticles. Therefore, after a large number of experiments by the inventors, it was found that the amount of dopamine hydrochloride added was 0.5g to 1.0g of dopamine hydrochloride per 10ml of water. At the same time, for the mixed solution, there is no fixed order of addition of the three, only a uniform solution needs to be formed in the end; at the same time, for the amount of ammonia water added, its too high or too low will affect the particle size of the polydopamine nanoparticles and the difficulty of subsequent centrifugal treatment, so the volume ratio of water, ethanol and ammonia water is set to 90:40:0.5 to 3.5, preferably 90:40:2.5.

[0018] Preferably, when the polydopamine nanoparticles obtained after the reaction are centrifuged, the centrifugal speed is 10000-12000 r / min, and the centrifugal time is 20-30 min. If the speed is too low, a large amount of polydopamine will remain in the supernatant; if the speed is too high, it will cause waste. At the same time, in order to remove the residual solvent and dopamine monomer in the solid phase, it can be washed with water several times, and after each washing, centrifugal separation is performed under the same conditions.

[0019] Another object of the present invention is to provide an oil-dispersible polydopamine nanoparticle prepared by any of the above methods.

[0020] Another object of the present invention is to provide the use of the above-mentioned oil-dispersible polydopamine nanoparticles, wherein the oil-dispersible polydopamine nanoparticles are used as lubricant additives, wherein the amount added is 0.3 to 1.5% of the lubricant base oil in terms of mass percentage.

[0021] An embodiment of the present invention is that the lubricating oil base oil is a polyethylene glycol base oil.

[0022] Beneficial effects: The present invention adopts a simple and controllable protonation reaction and anion transfer process to modify the fluorine-containing anions with good oil affinity onto the surface of polydopamine nanoparticles, successfully adjusts the oleophobicity of the polydopamine nanoparticles, and achieves its long-term dispersion stability in polyethylene glycol base oil for more than 30 days. The polydopamine nanoparticles prepared by the present invention can be directly dispersed in the polyethylene glycol lubricating base oil, and have an effective lubricating effect on the friction and wear between metal / metal friction pairs. This method avoids complex chemical reactions. At the same time, the phase transfer purification method eliminates the complicated centrifugal washing steps, the preparation conditions are mild, and there is no need for complex reaction equipment and dangerous drugs that are harmful to experimental personnel and the environment. The process is convenient and controllable, and has great application prospects. BRIEF DESCRIPTION OF THE DRAWINGS

[0023] Figure 1 This is the SEM morphology of the product of Example 1;

[0024] Figure 2 This is the XPS graph of the product of Example 1;

[0025] Figure 3 This is a stability test diagram of the product of Example 1;

[0026] Figure 4 This is a graph showing the lubrication performance test results of the product of Example 1;

[0027] Figure 5 This is a graph showing the anti-wear performance test results of the product of Example 1 based on the wear track. DETAILED DESCRIPTION

[0028] The specific implementation modes of the present invention will be described clearly and completely below with reference to examples. Obviously, the examples described are only some embodiments of the present invention, rather than all embodiments.

[0029] The present invention will be further described below in conjunction with embodiments:

[0030] In the following embodiments, unless otherwise specified, the operations described are routine operations in the art.

[0031] In the following examples, unless otherwise specified, the raw materials used can be obtained through conventional commercial channels.

[0032] Example 1

[0033] Preparation of polydopamine nanoparticles:

[0034] Take 10 ml of pure water, add 0.5 g of dopamine hydrochloride powder, and dissolve it by ultrasound to obtain a dopamine hydrochloride aqueous solution; stir and mix 90 ml of pure water, 40 ml of ethanol and 2.5 ml of ammonia water at 30°C for 30 minutes to obtain an alkaline mixed solution; add the dopamine hydrochloride aqueous solution dropwise to the mixed solution, continue stirring in a light-proof environment for 6 hours, and carry out an oxidative polymerization reaction of dopamine to obtain a polydopamine solution; centrifuge the obtained polydopamine solution at 11500 r / min for 25 minutes, then wash with water, and repeat the above operation 4 times to obtain polydopamine nanoparticles.

[0035] Preparation of oil-dispersible polydopamine nanoparticles:

[0036] Take 100 mg of polydopamine nanoparticles, disperse them with 20 ml of water, add 0.1 mol / L dilute hydrochloric acid to adjust the pH to 3.5, and continue stirring for 2 hours; add 20 ml of ethyl acetate, and under stirring, add 10 ml of 0.1 mol / L lithium bistrifluoromethanesulfonyl imide aqueous dispersion, and continue stirring for 30 minutes; separate the two-phase solution after the reaction, obtain the oil phase, and remove the solvent at 30°C to obtain oil-dispersible polydopamine nanoparticles.

[0037] Example 2

[0038] Preparation of polydopamine nanoparticles:

[0039] Take 10 ml of pure water, add 0.5 g of dopamine hydrochloride powder, and dissolve it by ultrasound to obtain a dopamine hydrochloride aqueous solution; stir and mix 90 ml of pure water, 40 ml of ethanol and 1.5 ml of ammonia water at 30°C for 30 minutes to obtain an alkaline mixed solution; add the dopamine hydrochloride aqueous solution dropwise to the mixed solution, continue stirring in a light-proof environment for 6 hours, and carry out an oxidative polymerization reaction of dopamine to obtain a polydopamine solution; centrifuge the obtained polydopamine solution at 11000 r / min for 30 minutes, then wash with water, and repeat the above operation 4 times to obtain polydopamine nanoparticles.

[0040] Preparation of oil-dispersible polydopamine nanoparticles:

[0041] Take 200 mg of polydopamine nanoparticles, disperse them with 30 ml of water, add 0.15 mol / L dilute hydrochloric acid to adjust the pH to 3, and continue stirring for 1.5 hours; add 30 ml of ethyl acetate, and under stirring, add 10 ml of 0.1 mol / L potassium hexafluorophosphate aqueous dispersion, and continue stirring for 30 minutes; separate the two-phase solution after the reaction, obtain the oil phase, and remove the solvent at 30°C to obtain oil-dispersible polydopamine nanoparticles.

[0042] Example 3

[0043] Preparation of polydopamine nanoparticles:

[0044] Take 10 ml of pure water, add 0.5 g of dopamine hydrochloride powder, and dissolve it by ultrasound to obtain a dopamine hydrochloride aqueous solution; stir and mix 90 ml of pure water, 40 ml of ethanol and 2.5 ml of ammonia water at 30°C for 30 minutes to obtain an alkaline mixed solution; add the dopamine hydrochloride aqueous solution dropwise to the mixed solution, continue stirring in a light-proof environment for 12 hours, and carry out an oxidative polymerization reaction of dopamine to obtain a polydopamine solution; centrifuge the obtained polydopamine solution at 11500 r / min for 25 minutes, then wash with water, and repeat the above operation 4 times to obtain polydopamine nanoparticles.

[0045] Preparation of oil-dispersible polydopamine nanoparticles:

[0046] Take 100 mg of polydopamine nanoparticles, disperse them with 20 ml of water, add 0.1 mol / L dilute hydrochloric acid to adjust the pH to 4, and continue stirring for 2 hours; add 20 ml of ethyl acetate, and under stirring, add 10 ml of 0.05 mol / L sodium tetrafluoroborate aqueous dispersion, and continue stirring for 45 minutes; separate the two-phase solution after the reaction, obtain the oil phase, and remove the solvent at 30°C to obtain oil-dispersible polydopamine nanoparticles.

[0047] In order to further illustrate the effect of the present invention, the oil-dispersible polydopamine nanoparticles of the above examples are specifically tested below.

[0048] 1. SEM analysis

[0049] The product of Example 1 was subjected to SEM analysis, and the final result was as follows: Figure 1 As shown. Figure 1 Figure a is the SEM morphology of polydopamine nanoparticles before modification. Figure 1 Figure b is the SEM morphology of the modified oil-dispersible polydopamine nanoparticles. Figure 1It can be seen that before modification, its shape is spherical and the average particle size is 112.8nm; after modification, the shape is still spherical, with basically no change, and the average particle size is 125.8nm, indicating that the modification process did not cause obvious damage to its morphology. At the same time, due to the increase in particle size, it also indicates that the modification is successful.

[0050] 2. XPS analysis

[0051] The product of Example 1 was subjected to XPS analysis, and the final result was as follows: Figure 2 As shown, from Figure 2 It can be seen that before modification, the polydopamine nanoparticles were mainly composed of C, N and O elements, while after modification, F and S elements were also detected in the oil-dispersible polydopamine nanoparticles, and no Cl element was detected, indicating that the ion exchange process was very thorough.

[0052] 3. Stability test

[0053] For lubricating oil additives, compatibility with lubricating oil is the primary condition. Take the product prepared in Example 1, add it to the polyethylene glycol base oil in an amount of 1wt%, and then measure its stability after standing for a period of time. Figure 3 As shown. Figure 3 It can be seen that the oil-dispersible polydopamine nanoparticles prepared in the embodiment of the present invention still did not precipitate after being added to the lubricating oil for 30 days, showing good stability. However, the polydopamine nanoparticles before modification were difficult to disperse in the oil and precipitated on the second day, showing poor stability.

[0054] 4. Anti-wear performance test

[0055] After adding the products of Examples 1, 2, and 3 to the base oil, the lubrication performance of the steel / steel friction pair was tested. The specific results are as follows: Figure 4 , Figure 5 See Figure 4 In a, the results show that after adding the oil-dispersible polydopamine of the embodiment of the present invention, the oil-dispersible polydopamine nanoparticles prepared in the embodiment of the present invention can play a good anti-wear and wear-reducing effect. Figure 4 b, indicating that the anti-friction performance of the lubricant is the best when the addition amount is 1.0wt%. Figure 5 , further illustrating that after adding the product of Example 1, the anti-wear performance of the lubricating oil can be effectively improved.

[0056] The above description is only a preferred embodiment of the present invention and does not constitute any form of limitation to the present invention. Although the present invention has been disclosed as a preferred embodiment as above, it is not intended to limit the present invention. Any technician familiar with the profession can make some changes or modifications to equivalent embodiments of equivalent changes using the technical contents disclosed above without departing from the scope of the technical solution of the present invention. However, any simple modification, equivalent change and modification made to the above embodiments based on the technical essence of the present invention without departing from the content of the technical solution of the present invention still falls within the scope of the technical solution of the present invention.

Claims

1. A method for preparing an oil-dispersible polydopamine nano-lubricating additive, characterized in that: The steps include: S1. Take polydopamine nanoparticles and disperse them in water. At 25-30° C., use dilute hydrochloric acid to adjust the pH of the dispersion to 3-4, and continue stirring for 1-2 hours to obtain a dispersion, wherein every 100-200 mg of polydopamine nanoparticles corresponds to 20-30 ml of water; the concentration of the dilute hydrochloric acid is 0.05-0.2 mol / L; S2, adding ethyl acetate to the dispersion after the reaction in S1, and then dropping a lipophilic fluorinated anion salt solution, and stirring for 0.5-1h, wherein every 20-30ml of water corresponds to 20-30ml of ethyl acetate, and the mass ratio of the lipophilic fluorinated anion salt to the polydopamine nanoparticles is 1.1-2.8:1; the lipophilic fluorinated anion salt is one of lithium bistrifluoromethanesulfonyl imide, potassium hexafluorophosphate and sodium tetrafluoroborate, and the concentration is 0.05-0.1mol / L; S3, obtain the oil phase of S2, and remove ethyl acetate; The preparation method of the polydopamine nanoparticles is as follows: dissolving dopamine hydrochloride in water, wherein the amount of dopamine hydrochloride added is 0.5 g to 1.0 g per 10 ml of water; taking water, ethanol and ammonia water in a volume ratio of 90:40:0.5 to 3.5, stirring for 30 minutes at 30° C. to obtain a mixed solution; mixing the dopamine hydrochloride solution and the mixed solution, and continuously stirring for 3 to 24 hours under light-proof conditions; and centrifuging and washing the product after the reaction to obtain the obtained product.

2. The preparation method according to claim 1, characterized in that: The centrifugal speed is 10000~12000 r / min, and the centrifugal time is 20~30min.

3. The preparation method according to claim 1, characterized in that: In S3, the ethyl acetate is removed at 25-30° C. under ventilation conditions.

4. An oil-dispersible polydopamine nanoparticle, characterized in that: The method is prepared by any one of claims 1 to 3.

5. Use of the oil-dispersible polydopamine nanoparticles according to claim 4, wherein the oil-dispersible polydopamine nanoparticles are used as lubricating oil additives, wherein: In terms of mass percentage, the amount added is 0.3~1.5% of the lubricating oil base oil.

6. The use of the oil-dispersible polydopamine nanoparticles according to claim 5, characterized in that: The lubricating oil base oil is polyethylene glycol base oil.

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