A method, apparatus and application for preparing lubricating oil microspheres based on microfluidic technology

Abstract

This invention discloses a method for preparing lubricating oil microspheres based on microfluidic technology, comprising: preparing an external phase solution, an intermediate phase solution, an internal phase solution, and a collection liquid; firstly, the internal phase solution is introduced into a microfluidic chip and allowed to flow stably, then the intermediate phase solution is introduced and sheared with the internal phase solution to form a core-shell structure. After the core-shell droplets have stabilized, the external phase solution is introduced into the microfluidic chip and sheared with the core-shell droplets to encapsulate them on the outer layer of the core, forming a core-shell structure. This dual-phase solution is then dropped into a collection liquid containing glutaraldehyde for cross-linking and solidification to form chitosan lubricating oil microspheres. This invention has the following advantages: by encapsulating lubricating oil inside the microspheres using microfluidic technology, the chitosan lubricating oil microspheres exhibit a core-shell structure, and the lubricating oil inside the microspheres is released when needed to improve the frictional performance of components.

Description

Technical Field

[0001] This invention belongs to the field of materials technology preparation and sustained release, specifically relating to a method, apparatus and application for preparing lubricating oil microspheres based on microfluidic technology. Background Technology

[0002] In fields with particularly high lubrication requirements, such as food and pharmaceuticals, microsphere-encapsulated lubricants can ensure the hygienic performance of equipment and prevent lubricant contamination of products. In the aerospace industry, microsphere-encapsulated lubricants can improve the lubrication of spacecraft components by releasing lubricant at certain temperatures when lubrication is lacking. Microsphere-encapsulated lubricant technology has the potential to play a role in various applications requiring efficient, long-lasting, and low-friction lubrication. The advantages of this technology include providing more durable lubrication, reducing the need for frequent maintenance, and potentially improving the overall performance of mechanical systems.

[0003] The fabrication of microspheres requires consideration of their size and particle size distribution, loading capacity and release performance, stability, and storage conditions. Among these, size and particle size distribution have the greatest impact on controlled-release microspheres. Droplet microfluidics are relatively simple to operate, producing microspheres with uniform size, closed systems, good monodispersity, and particle size deviation that can be stably controlled below 5%. Therefore, using microfluidic chips to fabricate microspheres is a good choice. Currently, the main microfluidic chips used for fabricating dual droplets are PDMS microfluidic chips and capillary microfluidic chips. When fabricating core-shell microspheres based on microfluidic chips, O / W / O or W / O / W type dual droplets need to be prepared. Therefore, the fabrication of both types of dual droplets requires modification of the microfluidic chip's internal structure. Since the channels of PDMS microfluidic chips are etched into the substrate using techniques such as photolithography, internal modification is relatively difficult. Glass capillary microfluidic chips, on the other hand, form channels through the assembly of capillaries, and internal channel modification only needs to be performed before assembly. Because the channels of a microfluidic chip are corroded by a solution after being introduced, affecting experimental results, microfluidic chips are consumables that require frequent replacement. Summary of the Invention

[0004] One object of the present invention is to solve at least the above-mentioned problems and / or defects, and to provide at least the advantages described below.

[0005] To achieve these objectives and other advantages according to the present invention, a method for preparing lubricating oil microspheres based on microfluidic technology is provided, comprising:

[0006] S1. Prepare an external phase solution, an intermediate phase solution, an internal phase solution, and a collection liquid, wherein the external phase solution is a high-viscosity mineral oil solution, the intermediate phase solution is a chitosan solution, and the internal phase solution is a low-viscosity mineral oil solution;

[0007] S2. First, the inner phase solution is introduced into the inner phase glass capillary. After the inner phase glass capillary is filled, the intermediate phase solution is injected into the intermediate phase glass capillary. The flow rate of the intermediate phase solution is adjusted so that it shears with the inner phase solution to form a stable flowing monoemulsion droplet. Then, the outer phase solution is injected into the outer phase glass capillary. The flow rate of the outer phase solution is adjusted so that the outer phase solution shears with the intermediate phase solution to encapsulate the monoemulsion droplet and form a double droplet.

[0008] S3. Then, drop the double droplets into the collection liquid. After the cross-linking and curing reaction occurs, microspheres are obtained. The mineral oil remaining on the surface of the microspheres is cleaned with isopropanol, and then the microspheres are cleaned with deionized water. Finally, they are placed in a vacuum drying oven for drying to obtain lubricating oil microspheres.

[0009] Preferably, in step S1, the external phase solution is prepared by mixing mineral oil with a viscosity of 35 and surfactant Span 80 at a volume ratio of 98-99:1-2, and then filtering the mineral oil solution through a 0.45μm needle filter membrane to obtain a high-viscosity mineral oil solution with added surfactant, which is then ready for use.

[0010] Preferably, in step S1, the intermediate phase solution is prepared as follows: chitosan powder with a degree of deacetylation greater than 90% is dissolved in deionized water, and glacial acetic acid is added to aid dissolution. The mixture is stirred in a heating stirrer for 2 hours, then 1-3g of polyvinyl alcohol is added, and the mixture is heated and stirred at 90°C for another 1 hour. The chitosan solution is then filtered through a 0.45μm needle filter membrane for later use. The mass-volume ratio of chitosan, deionized water, and glacial acetic acid is 0.5-1.5g:97-99mL:1-3mL.

[0011] Preferably, in step S1, the method for preparing the internal phase solution is as follows: mineral oil with a viscosity of 25 and surfactant Span 80 are mixed at a volume ratio of 98-99:1-2, and then the mineral oil solution is filtered through a 0.45μm needle filter membrane to obtain a low-viscosity mineral oil solution with added surfactant, which is then ready for use.

[0012] Preferably, in step S1, the method for preparing the collection liquid is as follows: take another external phase solution, add 1% of a 50% glutaraldehyde solution to it, and centrifuge the mixture in a centrifuge for 10 minutes to obtain a coagulation bath of the two, which is the collection liquid.

[0013] Preferably, in step S2, the flow rate of the inner phase solution is controlled at 0-5 ml / h, the flow rate of the intermediate phase solution is controlled at 0-5 ml / h, and the flow rate of the outer phase solution is controlled at 1-5 ml / min. In step S3, the ratio of the outer diameter to the inner diameter of the shell is 2, the outer diameter is 600-1200 μm, and the inner diameter is 300-600 μm.

[0014] An application of a method for preparing lubricating oil microspheres based on microfluidic technology: the prepared lubricating oil microspheres are used in bearing and gear systems of spacecraft.

[0015] An apparatus for preparing lubricating oil microspheres based on microfluidic technology, comprising:

[0016] Fluid injection unit;

[0017] A microfluidic chip includes a cover glass slide. A dispensing needle a is disposed on one side of the cover glass slide. The dispensing needle a is connected to an inner phase glass capillary. A portion of the inner phase glass capillary is nested within an intermediate phase glass capillary, and another portion of the intermediate phase glass capillary is nested within an outer phase glass capillary. A dispensing needle b is vertically disposed above the end of the intermediate phase glass capillary that overlaps with the inner phase glass capillary, and the dispensing needle b is in communication with the intermediate phase glass capillary. A dispensing needle c is vertically disposed above the end of the outer phase glass capillary that overlaps with the intermediate phase glass capillary, and the dispensing needle c is in communication with the outer phase glass capillary. The inner phase glass capillary, intermediate phase glass capillary, and outer phase glass capillary are coaxially arranged.

[0018] A microdroplet collection unit is located below the outer phase glass capillary;

[0019] The fluid injection unit includes a microfluidic controller, a sealed inlet bottle, and a pressure pump. The microfluidic controller is electrically connected to the pressure pump, the sealed inlet bottle is connected to the pressure pump, and the pressure pump is connected to the microfluidic chip.

[0020] Preferably, the portion of the inner phase glass capillary that overlaps with the intermediate phase glass capillary forms a shear zone a, and the portion of the intermediate phase glass capillary that overlaps with the outer phase glass capillary forms a shear zone b.

[0021] Preferably, the dispensing needle a includes a needle part a and a bottom a, the dispensing needle b includes a needle part b and a bottom b, and the dispensing needle c includes a needle part c and a bottom c. A groove I is formed on the bottom b, and a groove II is formed on the bottom c. The mesophase glass capillary passes through the groove I, and the outer phase glass capillary passes through the groove II. The bottom b is bonded to the end of the mesophase glass capillary that overlaps with the inner phase glass capillary, and the bottom c is bonded to the end of the outer phase glass capillary that overlaps with the mesophase glass capillary.

[0022] Preferably, the inner diameter of the dispensing needle a is the same as the outer diameter of the inner phase glass capillary, wherein the inner diameter of the inner phase glass capillary is 0.2 mm and the outer diameter is 0.34 mm; the inner diameter of the intermediate phase glass capillary is 0.5 mm and the outer diameter is 0.76 mm; and the inner diameter of the outer phase glass capillary is 0.9 mm and the outer diameter is 1.2 mm.

[0023] The present invention has at least the following beneficial effects:

[0024] (1) The chitosan lubricating oil microspheres prepared by the present invention have a uniform particle size distribution and a high loading capacity; and, by using microfluidic technology to encapsulate the lubricating oil inside the microspheres, the chitosan lubricating oil microspheres have a core-shell structure, and when lubricating oil is needed, the lubricating oil inside the microspheres is released to improve the friction performance of the parts.

[0025] (2) In this invention, chitosan material is used as the shell of lubricating oil microspheres, and further cross-linked and cured with glutaraldehyde to encapsulate the lubricating oil inside. Chitosan microspheres have good biocompatibility and biodegradability, which means that they can be naturally decomposed in the body or environment and will not cause long-term environmental pollution or have a negative impact on human health.

[0026] (3) This invention does not require expensive experimental equipment, has high precision, is simple to operate, and can be flexibly adjusted by the experimenter according to actual requirements; it has extremely high practical value.

[0027] (4) The lubricating oil microspheres prepared by the present invention have a core-shell structure, in which the core layer is lubricating oil and the shell layer is made of chitosan material. The core-shell microspheres can release lubricating oil in a specific environment to improve the friction environment.

[0028] (5) The experiment can be carried out at room temperature and pressure without the need for special experimental environments such as dust-free and constant temperature; at the same time, a large number of microspheres can be prepared in a short time.

[0029] Other advantages, objectives and features of the present invention will become apparent in part from the following description, and in part from those skilled in the art through study and practice of the invention. Attached image description:

[0030] Figure 1 This is an overall schematic diagram of the present invention;

[0031] Figure 2 This is a schematic diagram of the microfluidic chip in this invention;

[0032] Figure 3 This is a cross-sectional view of the microfluidic chip in this invention;

[0033] Figure 4 For the present invention Figure 2 Enlarged view of point A in the middle;

[0034] Figure 5 For the present invention Figure 2 Enlarged view at point B;

[0035] Figure 6 This is a structural diagram of the dispensing needle b of the present invention;

[0036] Figure 7 This is a structural diagram of the dispensing needle c of the present invention;

[0037] Figure 8 This is an optical micrograph of the double droplets prepared in Example 1 of the present invention;

[0038] Figure 9 This is a light microscope image of the lubricating oil microspheres prepared in Example 1 of the present invention;

[0039] Figure 10 This is an image of the lubricating oil microspheres prepared in Example 1 of the present invention under an optical camera. Detailed implementation method:

[0040] The present invention will now be described in further detail with reference to the accompanying drawings, so that those skilled in the art can implement it based on the description.

[0041] Example 1

[0042] like Figures 1-7 As shown, an apparatus for preparing chitosan lubricating oil microspheres includes:

[0043] Fluid injection unit 1;

[0044] Microfluidic chip 2 includes a cover glass 21. A dispensing needle a22 is provided on one side of the cover glass 21. The dispensing needle a22 is connected to an inner phase glass capillary 25. The inner phase glass capillary 25 is partially nested in an intermediate phase glass capillary 26. The intermediate phase glass capillary 26 is partially nested in an outer phase glass capillary 27. A dispensing needle b23 is vertically provided above the end of the intermediate phase glass capillary 26 that overlaps with the inner phase glass capillary 25. A dispensing needle c24 is vertically provided above the end of the outer phase glass capillary 27 that overlaps with the intermediate phase glass capillary 26.

[0045] The microdroplet collection unit 3 is located below the outer phase glass capillary 27.

[0046] Working principle:

[0047] The inner phase solution, intermediate phase solution, and outer phase solution in fluid injection unit 1 are sequentially introduced into microfluidic chip 2. Cover glass 21 is used to support the entire microfluidic chip 2. The specific process is as follows:

[0048] Using dispensing needle a 22, the inner phase solution is injected into the inner phase glass capillary 25 (inner diameter 0.2 mm, outer diameter 0.35 mm) at a flow rate of 2 ml / h. After the inner phase glass capillary 25 is fully filled, the intermediate phase solution is injected into the mesophase glass capillary 26 (inner diameter 0.5 μm, outer diameter 0.8 mm) using dispensing needle b 23, which is connected to the mesophase glass capillary 26. The flow rate of the mesophase solution is adjusted to 3.5 ml / h. After the mesophase solution enters the mesophase glass capillary 26, the inner phase solution and the intermediate phase solution are sheared at the end of the inner phase glass capillary 25 to form a stable monoemulsion droplet. Then, because the dispensing needle c 24 is connected to the outer phase glass capillary 27, the intermediate phase solution is injected into the mesophase glass capillary 26 (inner diameter 0.2 mm, outer diameter 0.35 mm) using dispensing needle c 22. 24. An external phase solution is injected into an external phase glass capillary 27 with an inner diameter of 1 mm and an outer diameter of 1.3 mm. The external phase solution enters the intermediate phase glass capillary 27. The intermediate phase solution and the external phase solution shear at the end of the intermediate phase glass capillary to encapsulate the single emulsion droplet into a double droplet. The double droplet is then dropped into the collection liquid of the microdroplet collection unit 3. It solidifies in the collection liquid to form chitosan lubricating oil microspheres. Then, the mineral oil remaining on the surface of the microspheres is cleaned with isopropanol, and the microspheres are cleaned with deionized water and then placed in a vacuum drying oven for drying.

[0049] In the above technical solution, the inner phase glass capillary 25, the intermediate phase glass capillary 26, and the outer phase glass capillary 27 are coaxially arranged. This coaxial arrangement of the inner phase glass capillary 25, the intermediate phase glass capillary 26, and the outer phase glass capillary 27 facilitates the manual fabrication of the microfluidic chip 2.

[0050] In the above technical solution, the portion where the inner phase glass capillary 25 overlaps with the mesophase glass capillary 26 forms a shear zone a 261, and the portion where the mesophase glass capillary 26 overlaps with the outer phase glass capillary 27 forms a shear zone b 271. The inner phase solution and the mesophase solution form a single emulsion droplet in shear zone a 261, and the single emulsion droplet and the outer phase solution form a double droplet in shear zone b 271.

[0051] In the above technical solution, the dispensing needle a 22 includes a needle portion a 221 and a bottom portion a 222, the dispensing needle b 23 includes a needle portion b 231 and a bottom portion b 232, and the dispensing needle c 24 includes a needle portion c 241 and a bottom portion c 242. The needle portion of all dispensing needles is used for injecting the solution, and the bottom portion of all dispensing needles is used to fix the components.

[0052] In the above technical solution, a groove I 41 is provided on the bottom b 232, a groove II 42 is provided on the bottom c 242, the intermediate phase glass capillary 26 passes through the groove I 41, and the outer phase glass capillary 27 passes through the groove II 42.

[0053] In the above technical solution, the bottom b 232 is bonded to the end of the mesophase glass capillary 26 that overlaps with the inner phase glass capillary 25, and the bottom c 242 is bonded to the end of the outer phase glass capillary 27 that overlaps with the mesophase glass capillary 26. Grooves I 41 and II 42 are used to hold and fix the mesophase glass capillary 26 and the outer phase glass capillary 27, respectively. At the same time, epoxy resin is used to fix each dispensing needle and each glass capillary and to seal the gaps.

[0054] In the above technical solution, the inner phase glass capillary 25 has an inner diameter of 0.2 mm and an outer diameter of 0.34 mm; the mesophase glass capillary 26 has an inner diameter of 0.5 mm and an outer diameter of 0.76 mm; and the outer phase glass capillary 27 has an inner diameter of 0.9 mm and an outer diameter of 1.2 mm. This arrangement of the inner and outer diameters of each glass capillary allows the mesophase solution and the outer phase solution to flow smoothly into the mesophase glass capillary 26 and the outer phase glass capillary 27, which is beneficial for the formation of double droplets.

[0055] In the above technical solution, the inner diameter of the dispensing needle a 22 is consistent with the outer diameter of the inner phase glass capillary 25. This consistency between the inner diameter of the dispensing needle a 22 and the outer diameter of the inner phase glass capillary 25 prevents leakage of the inner phase solution.

[0056] In the above technical solution, the fluid injection unit 1 includes a microfluidic controller 11, a sealed inlet bottle 13, and a pressure pump 12. The microfluidic controller 11 is electrically connected to the pressure pump 12, the sealed inlet bottle 13 is connected to the pressure pump 12, and the pressure pump 12 is connected to the microfluidic chip. The microfluidic controller 11 is used to control the pressure pump 12 to further control the fluid injection and flow rate, and the sealed inlet bottle 13 is used to store the fluid.

[0057] A method for preparing lubricating oil microspheres based on microfluidic technology, comprising:

[0058] S1. Prepare the external phase solution, intermediate phase solution, internal phase solution, and collection solution. The specific steps are as follows:

[0059] S11. Preparation of external phase solution: Select 98 ml of mineral oil with a viscosity of 35, add 2 ml of Span 80 and place it in a magnetic stirrer and stir at room temperature to obtain a mineral oil solution with 2 wt% surfactant. Then filter the mineral oil solution through a 0.45 μm needle filter membrane and store it for later use.

[0060] S12. Preparation of intermediate phase solution: Dissolve 0.5g of chitosan powder with a degree of deacetylation greater than 90% in 99ml of deionized water, then add 1ml of glacial acetic acid to aid dissolution. Stir the mixture in a magnetic stirrer for 2h to ensure the chitosan powder is fully dissolved in the deionized water to obtain a 0.5% chitosan solution. Then add 2g of polyvinyl alcohol and continue heating and stirring at 90℃ for 1h. Filter the chitosan solution through a 0.45μm needle filter membrane and store it for later use.

[0061] S13. Preparation of internal phase solution: Select 98 ml of mineral oil with a viscosity of 25, add 2 ml of Span 80 and place it in a magnetic stirrer and stir at room temperature to obtain a mineral oil solution with a volume fraction of 2% surfactant. Then filter the mineral oil solution through a 0.45 μm needle filter membrane and store it for later use.

[0062] S14. Preparation of the collection solution: Take another 5 mL of the external phase solution and add 0.05 mL of 50% glutaraldehyde to it. Centrifuge the mixture in a centrifuge for 10 min to obtain the coagulation bath of the two, which is the collection solution.

[0063] S2. The inner phase solution, intermediate phase solution, and outer phase solution are sequentially introduced into the microfluidic chip 2. Specifically: Dispensing needle a 22 injects the inner phase solution into the inner phase glass capillary 25 (inner diameter 0.2 mm, outer diameter 0.34 mm) at a flow rate of 2 ml / h. After the inner phase glass capillary 25 is fully filled, dispensing needle b 23 injects the intermediate phase solution into the intermediate phase glass capillary 26 (inner diameter 0.5 mm, outer diameter 0.76 mm). The flow rate of the intermediate phase solution is adjusted to 3.5 ml / h. After it can shear with the inner phase solution to form a stable single emulsion droplet, dispensing needle c 24 injects the outer phase solution into the outer phase glass capillary 27 (inner diameter 0.9 mm, outer diameter 1.2 mm). The flow rate of the outer phase solution is adjusted to 2 ml / min, so that the outer phase solution shears with the intermediate phase solution to encapsulate the single emulsion droplet into a double droplet.

[0064] S3. Then, drop the double droplets into the collection liquid of the microdroplet collection unit 3 to allow the chitosan and glutaraldehyde to undergo a cross-linking and curing reaction to obtain microspheres. Clean the mineral oil residue on the surface of the microspheres with isopropanol, then clean the microspheres with deionized water, and then place them in a vacuum drying oven to dry, thus obtaining lubricating oil microspheres.

[0065] Figure 8 The double droplets obtained from S2 show that they form a core-shell structure, with chitosan perfectly encapsulating the lubricating oil. Before solidification, the outer diameter of the chitosan is approximately 980 μm.

[0066] Figure 9 The light microscopy image of the final lubricating oil microspheres shows that the slightly yellowish outer layer is chitosan, and the shaded inner part is the encapsulated lubricating oil. Moreover, chitosan lubricating oil microspheres encapsulating one or two lubricating oils can be prepared. The outer diameter of the solidified microspheres becomes about 760 μm, and the shrinkage rate is about 23%.

[0067] Figure 10 The image of the final lubricating oil microspheres under an optical camera shows that the outer shell is slightly yellowish chitosan, and the inner layer is encapsulated lubricating oil.

[0068] Example 2

[0069] A method for preparing lubricating oil microspheres based on microfluidic technology, comprising:

[0070] S1. Prepare the external phase solution, intermediate phase solution, internal phase solution, and collection solution. The specific steps are as follows:

[0071] S11. Preparation of external phase solution: Select 98 ml of mineral oil with a viscosity of 35, add 2 ml of Span 80 and place it in a magnetic stirrer and stir at room temperature to obtain a mineral oil solution with 2 wt% surfactant. Then filter the mineral oil solution through a 0.45 μm needle filter membrane and store it for later use.

[0072] S12. Preparation of intermediate phase solution: Dissolve 1g of chitosan powder with a degree of deacetylation greater than 90% in 99ml of deionized water, then add 1ml of glacial acetic acid to aid dissolution. Stir the mixture in a magnetic stirrer for 2h to ensure that the chitosan powder is fully dissolved in the deionized water to obtain a 1% chitosan solution. Then add 2g of polyvinyl alcohol and continue heating and stirring at 90℃ for 1h. Filter the chitosan solution through a 0.45μm needle filter membrane and store it for later use.

[0073] S13. Preparation of internal phase solution: Select 98 ml of mineral oil with a viscosity of 25, add 2 ml of Span 80 and place it in a magnetic stirrer and stir at room temperature to obtain a mineral oil solution with a volume fraction of 2% surfactant. Then filter the mineral oil solution through a 0.45 μm needle filter membrane and store it for later use.

[0074] S14. Preparation of the collection solution: Take another 5 mL of the external phase solution and add 0.05 mL of 50% glutaraldehyde to it. Centrifuge the mixture in a centrifuge for 10 min to obtain the coagulation bath of the two, which is the collection solution.

[0075] S2. The inner phase solution, intermediate phase solution, and outer phase solution are sequentially introduced into the microfluidic chip 2. Specifically: Dispensing needle a 22 injects the inner phase solution into the inner phase glass capillary 25 (inner diameter 0.2 mm, outer diameter 0.34 mm) at a flow rate of 2 ml / h. After the inner phase glass capillary 25 is fully filled, dispensing needle b 23 injects the intermediate phase solution into the intermediate phase glass capillary 26 (inner diameter 0.5 mm, outer diameter 0.76 mm). The flow rate of the intermediate phase solution is adjusted to 3.5 ml / h. After it can shear with the inner phase solution to form a stable single emulsion droplet, dispensing needle c 24 injects the outer phase solution into the outer phase glass capillary 27 (inner diameter 0.9 mm, outer diameter 1.2 mm). The flow rate of the outer phase solution is adjusted to 2 ml / min, so that the outer phase solution shears with the intermediate phase solution to encapsulate the single emulsion droplet into a double droplet.

[0076] S3. Then, drop the double droplets into the collection liquid of the microdroplet collection unit 3 to allow the chitosan and glutaraldehyde to undergo a cross-linking and curing reaction to obtain microspheres. Clean the mineral oil residue on the surface of the microspheres with isopropanol, then clean the microspheres with deionized water, and then place them in a vacuum drying oven to dry, thus obtaining lubricating oil microspheres.

[0077] Example 3

[0078] A method for preparing lubricating oil microspheres based on microfluidic technology, comprising:

[0079] S1. Prepare the external phase solution, intermediate phase solution, internal phase solution, and collection solution. The specific steps are as follows:

[0080] S11. Preparation of external phase solution: Select 98 ml of mineral oil with a viscosity of 35, add 2 ml of Span 80 and place it in a magnetic stirrer and stir at room temperature to obtain a mineral oil solution with 2 wt% surfactant. Then filter the mineral oil solution through a 0.45 μm needle filter membrane and store it for later use.

[0081] S12. Preparation of intermediate phase solution: Dissolve 1.5g of chitosan powder with a degree of deacetylation greater than 90% in 99ml of deionized water, then add 1ml of glacial acetic acid to aid dissolution. Stir the mixture in a magnetic stirrer for 2 hours to ensure the chitosan powder is fully dissolved in the deionized water to obtain a 1.5% chitosan solution. Then add 2g of polyvinyl alcohol and continue heating and stirring at 90℃ for 1 hour. Filter the chitosan solution through a 0.45μm needle filter membrane and store it for later use.

[0082] S13. Preparation of internal phase solution: Select 98 ml of mineral oil with a viscosity of 25, add 2 ml of Span 80 and place it in a magnetic stirrer and stir at room temperature to obtain a mineral oil solution with a volume fraction of 2% surfactant. Then filter the mineral oil solution through a 0.45 μm needle filter membrane and store it for later use.

[0083] S14. Preparation of the collection solution: Take another 5 mL of the external phase solution and add 0.05 mL of 50% glutaraldehyde to it. Centrifuge the mixture in a centrifuge for 10 min to obtain the coagulation bath of the two, which is the collection solution.

[0084] S2. The inner phase solution, intermediate phase solution, and outer phase solution are sequentially introduced into the microfluidic chip 2. Specifically: Dispensing needle a 22 injects the inner phase solution into the inner phase glass capillary 25 (inner diameter 0.2 mm, outer diameter 0.34 mm) at a flow rate of 2 ml / h. After the inner phase glass capillary 25 is fully filled, dispensing needle b 23 injects the intermediate phase solution into the intermediate phase glass capillary 26 (inner diameter 0.5 mm, outer diameter 0.76 mm). The flow rate of the intermediate phase solution is adjusted to 3.5 ml / h. After it can shear with the inner phase solution to form a stable single emulsion droplet, dispensing needle c 24 injects the outer phase solution into the outer phase glass capillary 27 (inner diameter 0.9 mm, outer diameter 1.2 mm). The flow rate of the outer phase solution is adjusted to 2 ml / min, so that the outer phase solution shears with the intermediate phase solution to encapsulate the single emulsion droplet into a double droplet.

[0085] S3. Then, drop the double droplets into the collection liquid of the microdroplet collection unit 3 to allow the chitosan and glutaraldehyde to undergo a cross-linking and curing reaction to obtain microspheres. Clean the mineral oil residue on the surface of the microspheres with isopropanol, then clean the microspheres with deionized water, and then place them in a vacuum drying oven to dry, thus obtaining lubricating oil microspheres.

[0086] Application examples

[0087] The lubricating oil microspheres prepared in Example 1 were added to lubricating oil and used in the bearing and gear systems of spacecraft for space simulation experiments. Since the bearings and gear systems of spacecraft need to operate in low-temperature or vacuum environments, they are sealed during use. When the internal lubricating oil is depleted and cannot be replenished in time under low-temperature and vacuum conditions, the frictional heat generated by the bearings and gear systems causes the temperature to reach 60-80°C. At this point, the chitosan on the outside of the lubricating oil microspheres begins to soften, which may lead to rupture or leakage of the microsphere shell under sustained high temperatures, allowing the microspheres to release the lubricating oil. By using microspheres to release lubricating oil in a controlled manner, a low coefficient of friction can be maintained on the surface of mechanical parts. The released lubricating oil can increase the bearing life from 1000 hours to over 4000 hours. Without lubricating oil microspheres, the life of the gear system would be shortened by 60-80%, and it would fail rapidly even under light load conditions. In addition, the chitosan shell can be chemically modified to decompose when exposed to certain environmental stimuli (such as acidification of the friction pair surface). In the later stage, polyethylene glycol or graphene can be added to the chitosan solution to improve the overall flexibility and strength of the microspheres.

[0088] Although embodiments of the present invention have been disclosed above, they are not limited to the applications listed in the specification and embodiments. They can be applied to various fields suitable for the present invention. For those skilled in the art, other modifications can be easily made. Therefore, without departing from the general concept defined by the claims and their equivalents, the present invention is not limited to the specific details and illustrations shown and described herein.

Claims

1. An application of lubricating oil microspheres, characterized in that, The lubricating oil microspheres are used in the bearing and gear systems of spacecraft; The method for preparing the lubricating oil microspheres is as follows: S1. Prepare an external phase solution, an intermediate phase solution, an internal phase solution, and a collection liquid, wherein the external phase solution is a high-viscosity mineral oil solution, the intermediate phase solution is a chitosan solution, and the internal phase solution is a low-viscosity mineral oil solution; S2. First, the inner phase solution is introduced into the inner phase glass capillary. After the inner phase glass capillary is filled, the intermediate phase solution is injected into the intermediate phase glass capillary. The flow rate of the intermediate phase solution is adjusted so that it shears with the inner phase solution to form a stable flowing monoemulsion droplet. Then, the outer phase solution is injected into the outer phase glass capillary. The flow rate of the outer phase solution is adjusted so that the outer phase solution shears with the intermediate phase solution to encapsulate the monoemulsion droplet to form a double droplet. S3. Drop the double droplets into the collection liquid to obtain microspheres. Wash the microspheres and dry them to obtain lubricating oil microspheres with a core layer of lubricating oil and a shell layer of chitosan. In S1, the external phase solution is prepared by mixing mineral oil with a viscosity of 35 and surfactant Span 80 at a volume ratio of 98-99:1-2, and then filtering the mixture through a 0.45μm needle filter membrane to obtain a high-viscosity mineral oil solution. The intermediate phase solution is prepared by dissolving chitosan powder with a degree of deacetylation greater than 90% in deionized water, adding glacial acetic acid for solubilization, stirring the mixture in a heated stirrer for 2 hours, adding 1-3g of polyvinyl alcohol, stirring at 90℃ for 1 hour, and then filtering the mixture through a 0.45μm needle filter membrane. Filtration; wherein the mass-to-volume ratio of chitosan, deionized water, and glacial acetic acid is 0.5-1.5g:97-99mL:1-3mL; the internal phase solution is prepared by mixing mineral oil with a viscosity of 25 and surfactant Span 80 at a volume ratio of 98-99:1-2, and then filtering it through a 0.45μm needle filter membrane to obtain a low-viscosity mineral oil solution; the collected liquid is prepared by taking another external phase solution, adding 1% of a 50% glutaraldehyde solution to it, mixing it, and then centrifuging it in a centrifuge for 10 minutes to obtain a coagulation bath; In step S2, the flow rate of the inner phase solution is 0-5 ml / h, the flow rate of the intermediate phase solution is 0-5 ml / h, and the flow rate of the outer phase solution is 1-5 ml / min. In step S3, the ratio of the outer diameter to the inner diameter of the shell is 2, the outer diameter is 600-1200 μm, and the inner diameter is 300-600 μm.

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