Functionalized thermal alarm self-healing microcapsule based on microfluidic with double-layer nested structure and preparation method thereof

Abstract

The application discloses a functionalized heat alarm self-healing microcapsule with a double-layer nested structure based on microfluidics, which comprises an inner core and a microcapsule shell, and the inner core and the microcapsule shell are in a double-layer nested structure. The inner core is a heat alarm microcapsule and isophrone diisocyanate. The microcapsule shell is Fe3O4@SiO2 nanoparticle embedded microcapsule shell, which is composed of Fe3O4@SiO2 nanoparticles, an emulsifier, TDI prepolymer, an organic solvent and a crosslinking agent. Through the design of the double-layer nested structure, the microcapsule is bifunctionalized, can independently repair the microscale electric tree damage caused by electric heating stress, has good thermochromism, can perceive the local overheating of the insulating material in advance, gives a timely early warning before the electric tree damage occurs, and the two functions do not affect each other.

Description

Technical Field

[0001] This invention belongs to the field of high voltage insulation materials, and in particular to functionalized thermal alarm self-healing microcapsules with a double-layer nested structure based on microfluidics and their preparation method. Background Technology

[0002] With the rapid development of ultra-high voltage (UHV) power transmission technology and new power systems, high-voltage power equipment and power electronic equipment play a crucial role in the intelligentization and miniaturization of power systems, influencing their stable operation and intelligent control. However, electrical equipment is inevitably affected by numerous factors during long-term operation (such as extreme weather conditions like high temperatures and extreme cold, electromagnetic interference, and thermal stress), which can easily lead to localized overheating and minor defects in the main insulation materials, causing irreversible insulation damage and ultimately resulting in equipment insulation failure or even power grid collapse. Therefore, early warning of locally concentrated electrothermal stress in insulation materials and targeted repair at the early stage of minor damage are of great significance.

[0003] Current research on overheat warning and insulation performance of power equipment mainly focuses on online monitoring of equipment temperature using conventional active sensors and numerous novel passive sensing technologies (infrared detection, fiber optic sensing, thermocouple sensing, surface acoustic wave technology, etc.) and enhancing the overall insulation performance of power equipment by doping inorganic nanoparticles into insulating materials to delay damage. However, the industrial application of heat warning and nanoparticle doping is limited and remains uncertain for the following reasons: (1) Doping with nanoparticles can only delay damage but cannot repair it. Once micro-damage occurs inside the material, it will eventually lead to irreversible insulation failure; (2) The addition of nanoparticles increases the dielectric loss of the material, which can easily generate more heat and thus accelerate the aging and cracking of the material; (3) Existing temperature detection technologies have disadvantages such as being limited by the environment (dust, etc.), complex equipment, and high cost. They also lack the ability to sense local overheating of materials and provide immediate alarms.

[0004] Currently, microencapsulation technology is widely used in fields such as thermochromism and material repair. By incorporating microcapsules with specific functions into insulating materials, the materials can achieve the corresponding functions, thereby reducing the costs and expenses of online monitoring and fault repair of equipment, and has broad application prospects.

[0005] In summary, researching an intelligent capsule that can both detect local overheating in real time and issue early warning signals, and autonomously repair internal damage, can provide a new solution for timely detection of local overheating and autonomous repair of minor damage, thereby ensuring the safety of equipment during use and improving its service life. Summary of the Invention

[0006] To improve the fabrication processability and application versatility of microcapsules in the power equipment field, this invention proposes a functionalized thermal alarm self-healing (HASH) microcapsule with a double-layer nested structure and its preparation method, based on a microfluidic technology platform. The prepared HASH microcapsules can be artificially magnetically targeted to areas of the insulating material prone to localized overheating and stress damage. They exhibit good dispersibility, integrity, thermochromic properties, and resistance to breakage, enabling them to provide timely alarms for localized overheating and automatically repair early damage defects when incorporated into the matrix material.

[0007] Technical solution:

[0008] This invention first discloses a functionalized thermal alarm self-healing microcapsule based on microfluidics and featuring a double-layered nested structure. It comprises an inner core and a microcapsule shell, the inner core and the microcapsule shell forming a double-layered nested structure, wherein:

[0009] The inner core consists of: thermal alarm (HA) microcapsules and isophorone diisocyanate (IPDI).

[0010] The microcapsule shell is composed of Fe3O4@SiO2 nanoparticles embedded in it, and is made of Fe3O4@SiO2 nanoparticles, emulsifier, TDI prepolymer, organic solvent, and crosslinking agent. The mass ratio of Fe3O4@SiO2 nanoparticles, emulsifier, toluene diisocyanate (TDI), organic solvent, and crosslinking agent is 1:11-15:10:22-24:7-8.

[0011] In a preferred embodiment, the emulsifier is gum arabic, the organic solvent is chlorobenzene, and the crosslinking agent is 1,4-butanediol.

[0012] Preferably, the mass ratio of the inner core to the microcapsule shell is: the mass ratio of the thermal alarm (HA) microcapsule to isophorone diisocyanate (IPDI) is 1 to 2:2.

[0013] Preferably, the microcapsules have a particle size of 200–220 μm.

[0014] Preferably, the wall thickness of the microcapsule shell is 3 to 5 μm.

[0015] Preferably, the microcapsule shell contains urethane (NHCOO) groups.

[0016] Preferably, the decomposition temperature of the microcapsule shell is 162°C; and the decomposition temperature of the inner core is 230°C.

[0017] Preferably, the inner core and the surface of the microcapsule shell have carbon, iron and silicon elements.

[0018] This invention also discloses a method for preparing functionalized thermal alarm self-healing microcapsules with a double-layer nested structure based on microfluidics, which includes the following steps:

[0019] S1. Fabrication of microfluidic devices;

[0020] S2. Preparation of Fe3O4@SiO2 core-shell nanoparticles;

[0021] S3. Preparation of thermal alarm HA microcapsules;

[0022] S3-1. Preparation of melamine-formaldehyde MF prepolymer: Weigh melamine and formaldehyde in a mass ratio of 1-5:2-8 into a three-necked flask, mix with 100 mL of deionized water, stir magnetically to mix thoroughly, add triethanolamine to adjust the pH of the mixture to 8-9 to carry out the polymerization reaction, and heat in a constant temperature water bath at 45-55℃ for 15-25 min to obtain the MF prepolymer;

[0023] S3-2. Preparation of a homogeneous oil-water mixture:

[0024] S3-2-1. Preparation of oil phase: Weigh fluorescent red HFG, bisphenol A and 1-hexadecanool in a mass ratio of 1:1 to 3:40 to 60 into a three-necked flask and mechanically stir in a constant temperature water bath at 70 to 80°C for 25 to 35 minutes to obtain the oil phase.

[0025] S3-2-2, Preparation of aqueous phase: Weigh styrene-maleic anhydride copolymer (SMA), sodium hydroxide, and deionized water in a mass ratio of 1:0.2 to 1:90 to 100, and magnetically stir them at 50 to 70°C for 50 to 60 minutes to obtain the aqueous phase;

[0026] S3-2-3. Preparation of a homogeneous oil-water system: The oil phase is slowly added to the water phase, with a mass ratio of oil phase to water phase of 5:90-100. At the same time, citric acid solution is added dropwise to adjust the pH of the mixture to 5-6. The mixture is then kept in a constant temperature water bath at 60-80℃ for 20-40 minutes to obtain a homogeneous oil-water system.

[0027] S3-3, Preparation of HA microcapsules: The prepared MF prepolymer was slowly pumped into a homogeneous oil-water system at a rate of 1 mL / min, with a volume ratio of MF prepolymer to oil-water system of 1:1; under constant temperature water bath conditions of 60-80℃, citric acid was added dropwise to a three-necked flask at a rate of 0.2-0.4 mL / min to adjust the pH of the mixture to 4-5, and the mixture was heated in the water bath for 1 hour; sodium hydroxide solution was added dropwise to the mixture to adjust the pH to neutral, and then the mixture was stirred continuously for 15-30 minutes before heating was stopped. After cooling to room temperature, the suspension was filtered, washed, and dried to obtain HA microcapsule powder;

[0028] S4. Preparation of thermal alarm self-healing HASH microcapsules with a double-layer nested structure:

[0029] S4-1. Preparation of water / oil / solid composite emulsion:

[0030] S4-1-1 Preparation of aqueous phase: At room temperature, take 110-130 mL of deionized water into a beaker, place it on a magnetic stirrer, add 5-7 g of gum arabic (GA) during stirring, and stir for 2-3 hours until the GA is completely dissolved.

[0031] S4-1-2, Preparation of the oil phase: Weigh toluene diisocyanate (TDI), chlorobenzene CB, isophorone diisocyanate (IPDI), and HA microcapsule powder prepared in S3-3 in a mass ratio of 1:2.2-2.4:3:1.5-3; Dissolve the weighed TDI in CB and stir magnetically for 10-15 minutes. After the solid is completely dissolved, add the weighed IPDI and HA microcapsule powder and mix them evenly to obtain an oil-solid blend.

[0032] S4-1-3. Preparation of composite emulsion: Extract the aqueous phase using two syringes and the oil phase using one syringe; assemble the syringes with matching soft tubing and stainless steel needles, and place the syringes on a peristaltic pump, inserting the needle into the hole at the center of the PDMS; adjust the flow rate of the aqueous phase to 150-250 μL / min and the flow rate of the oil phase to 40-60 μL / min, and finally collect the water / oil / solid composite emulsion with uniform diameter.

[0033] S4-2, Preparation of HASH microcapsules:

[0034] Fe3O4@SiO2 nanoparticles were added to the composite emulsion prepared in S4-1-3 and ultrasonically dispersed for 3 h. Then, the mixture was placed in a 50℃ oil bath and magnetically stirred. 1,4-Butanediol was slowly added dropwise and stirred for 10-20 min. The oil bath temperature was then increased to 70℃ and stirred for 1-2 h to obtain a suspension.

[0035] After the suspension has cooled to room temperature, rinse it repeatedly with deionized water 3 to 5 times, separate by decanting, and filter it with a Bukner funnel.

[0036] Finally, air dry in a cool place to obtain HASH microcapsules.

[0037] Preferably, the fabrication of the microfluidic device in S1 specifically includes the following steps:

[0038] S1-1, Preparation of microfluidic channels:

[0039] First, take a certain amount of concentrated sulfuric acid solution and hydrogen peroxide in a volume ratio of 7:3, stir well, and then soak the silicon wafer in the solution for 15-20 minutes. After washing it several times with deionized water, acetone and anhydrous ethanol, blow it dry with nitrogen gas and place it on a beaker. Take another beaker and add 1-2 drops of hexamethyldisilane to it. Place both beakers in a vacuum chamber and dry for 3-5 minutes.

[0040] Then, the dried silicon wafer is placed in the center of a spin coater, and 4-5 mL of SU-8-2000 photoresist is poured onto the silicon wafer. The spin coater is set to 200 r / min for 20 s and 1300 r / min for 50 s. The silicon wafer coated with photoresist is then placed on a heating stage for soft baking at 60-65°C for 6-8 min, followed by baking at 90-95°C for 40-45 min. After baking, the wafer is placed on a photomask for UV exposure for 45 s to 1 min, followed by baking at 60-65°C for 6-8 min and then baking at 90-95°C for 10-15 min to enhance the baking effect.

[0041] Finally, excess photoresist was cleaned sequentially using SU-8-2000 developer, acetone, ethanol and deionized water. After drying with nitrogen, 2-3 drops of 1H1H2H2H-perfluorooctylmethyldichlorosilane were added and stored in a sealed space for more than 12 hours to obtain a silicon wafer containing microfluidic channels.

[0042] S1-2, Fabrication of microfluidic devices:

[0043] The polydimethylsiloxane (PDMS) prepolymer with a mass ratio of 10:1 to 1.5 and its corresponding curing agent are stirred and mixed evenly, and after defoaming in a vacuum drying oven, it is poured onto the silicon wafer prepared in S1-1. The silicon wafer coated with PDMS is cured in an oven at 50 to 55°C for 3 to 4 hours.

[0044] After curing, use the included punch to drill a hole in the center of the PDMS and cut it into the required shape and size;

[0045] Finally, a plasma bonding machine was used to bond the glass plate to the PDMS plate to seal the microfluidic channel.

[0046] Preferably, the preparation of Fe3O4@SiO2 core-shell nanoparticles in S2 specifically includes the following steps:

[0047] S2-1. Preparation of Fe3O4 nanoparticles: Take ferric chloride hexahydrate, trisodium citrate dihydrate, and sodium acetate in a mass ratio of approximately 4:6:0.3-0.4. Dissolve the ferric chloride hexahydrate and trisodium citrate dihydrate completely in ethylene glycol (EG). Stir magnetically for 1-2 hours, then add sodium acetate and continue stirring for another 8-9 hours. After the reagents have fully reacted, pour the mixture into a stainless steel autoclave lined with a polytetrafluoroethylene inner cylinder and heat at 180-220°C for 10-11 hours. When it cools to room temperature, remove the supernatant, collect the prepared Fe3O4 nanoparticles using a permanent magnet, transfer them to a beaker, and bring the volume to a final volume.

[0048] S2-2, Preparation of Fe3O4@SiO2 core-shell nanoparticles: The Fe3O4 nanoparticles prepared in S2-1 were uniformly dispersed in a slanted three-necked sphere containing concentrated ammonia and anhydrous ethanol. The mixture was heated and mechanically stirred for 30 min under water bath conditions. Tetraethyl silicate (TEOS) was added dropwise, and stirring was continued for 12-13 h after the addition was complete. After the reaction was completed, the supernatant was removed, and the obtained Fe3O4@SiO2 core-shell nanoparticles were collected by magnetic separation, washed, and diluted to a fixed volume.

[0049] Beneficial effects of the present invention

[0050] Most existing multifunctional microcapsules can only achieve single functions such as thermochromism at certain temperatures or self-repair upon damage. Furthermore, due to the dispersibility of microcapsules during doping, they cannot provide early warning and repair of damage in specific areas. Simultaneously, the instability of the oil-water system during preparation makes it difficult to achieve the ideal droplet diameter, thus affecting the microcapsule size and consequently the performance of the composite material formed when the microcapsules are mixed with the substrate. The HASH microcapsules prepared in this invention have an average particle size of 210 μm and good dispersibility. Simultaneously, due to nano-doping modification of their outer shell, they possess a certain magnetic force, enabling them to be directionally distributed within the material's overheat-prone and damage-prone areas under the influence of an external magnetic field. They exhibit significant discoloration at specific temperatures and break down upon minor damage, enabling large-scale temperature detection and overheat warning for power equipment over a long lifespan. This effectively extends the service life of power system and power electronic insulation materials, providing a new approach and solution for ensuring the safe and stable operation of the power grid. Attached Figure Description

[0051] Figure 1 This is a schematic diagram illustrating the function of the double-layer nested HASH microcapsule structure in the embodiment.

[0052] Figure 2 This is a diagram illustrating the fabrication process of the microfluidic device in the embodiment.

[0053] Figure 3 This is a diagram illustrating the preparation process of Fe3O4@SiO2 core-shell nanoparticles in the examples.

[0054] Figure 4 This is a diagram illustrating the preparation process of HA microcapsules in the examples.

[0055] Figure 5 This is a diagram illustrating the preparation process of the HASH microcapsules in this embodiment.

[0056] Figure 6 Optical images of microdroplets in the examples

[0057] Figure 7 The microdroplet size distribution diagram is shown in the example.

[0058] Figure 8 SEM images of HASH microcapsules in the examples

[0059] Figure 9 The above is the FT-IR spectrum of the HASH microcapsules in the example.

[0060] Figure 10 EDS distribution diagram of HASH microcapsules in the embodiment.

[0061] Figure 11 The TGA curve of the HASH microcapsules in the embodiment.

[0062] Figure 12 The image shows the color change of the epoxy composite material doped with 0.5 wt% HASH microcapsules during the heating-cooling cycle in the examples.

[0063] Figure 13 Fluorescence image of the mechanical damage healing effect in the examples

[0064] Figure 14 Fluorescence image of the healing effect of electrical tree damage in the embodiment. Detailed Implementation

[0065] The present invention will be further described below with reference to embodiments, but the scope of protection of the present invention is not limited thereto:

[0066] This invention utilizes a microfluidic platform to construct a HASH microcapsule with a double-layered nested structure. Fe3O4@SiO2 nanoparticles are embedded within the microcapsule shell to provide magnetic traction, enabling the prepared microcapsules to migrate to areas of concentrated electrothermal stress and micro-damage in the insulating material under the guidance of a directional magnetic field. In the event of an overheating fault, the HASH microcapsule can sense the temperature change over time, producing a visible color change, thus enabling temperature monitoring and overheat warning for the power equipment. Simultaneously, when the insulating material of the equipment experiences unavoidable internal damage, the HASH microcapsule can be triggered to rupture due to the progression of the damage, causing the encapsulated healing agent to leak out and be exposed to ambient moisture, resulting in a curing reaction that repairs the existing micro-damage. The basic principle of the entire process is as follows: Figure 1 As shown.

[0067] The manufacturers and purities of the chemical reagents used in the functionalized thermal alarm self-healing (HASH) microcapsules with a double-layer nested structure based on microfluidic technology proposed in this invention are shown in Table 1:

[0068] Table 1: Manufacturers and Purity of Chemical Reagents Used in the HASH Microcapsules in the Examples

[0069]

[0070]

[0071] The main experimental instruments used in the preparation of a functionalized thermal alarm self-healing (HASH) microcapsule with a double-layer nested structure based on microfluidic technology in this invention are listed in Table 2.

[0072] Table 2: Models and Manufacturers of the Main Experimental Instruments Used in the Examples of HASH Microcapsules

[0073]

[0074]

[0075] Table 3 lists the models and manufacturers of the main experimental instruments used in the method of this invention to characterize and test the performance of a functionalized thermal alarm self-healing (HASH) microcapsule with a double-layer nested structure based on microfluidic technology.

[0076] Table 3: Models and Manufacturers of Main Experimental Instruments Used for HASH Microcapsule Testing in the Examples

[0077]

[0078] The method for preparing a functionalized thermal alarm self-healing (HASH) microcapsule with a double-layer nested structure based on microfluidic technology in this invention includes the following steps:

[0079] S1. Reference Figure 2 Fabrication of microfluidic devices:

[0080] S1-1. Preparation of Microfluidic Channels: Measure 70 mL of concentrated sulfuric acid solution and 30 mL of hydrogen peroxide into a 500 mL beaker, stir well, and then immerse the silicon wafer in the solution for 15 min. Clean the wafer repeatedly with deionized water, acetone, and anhydrous ethanol, then dry it with nitrogen gas and place it on a beaker. In another beaker, add 2 drops of hexamethyldisilane. Place both beakers in a vacuum chamber and dry for 3 min. Then, place the dried silicon wafer in the center of a spin coater, pour 4 mL of SU-8-2000 photoresist onto the wafer, and spin coat the photoresist at 200 r / min for 20 s and 1300 r / min for 50 s. Place the photoresist-coated silicon wafer on a heating stage for soft baking at 65°C for 7 min, followed by baking at 95°C for 45 min. After baking, the wafer was placed on a photomask for UV exposure for 45 seconds, then baked at 65°C for 7 minutes and at 95°C for 15 minutes to enhance the baking effect. Finally, excess photoresist was cleaned sequentially using SU-8-2000 developer, acetone, ethylene propanol, and deionized water. After drying with nitrogen, two drops of 1H1H2H2H-perfluorooctylmethyldichlorosilane were added, and the wafer was stored in a sealed space for more than 12 hours to obtain a silicon wafer containing microfluidic channels.

[0081] S1-2, Preparation of the microfluidic device: Weigh 35g of polydimethylsiloxane (PDMS) prepolymer and 3.5g of its corresponding curing agent, stir and mix them evenly, and after defoaming in a vacuum drying oven, pour them onto the silicon wafer prepared in S1-1. Cure the PDMS-coated silicon wafer in an oven at 50℃ for 4 hours. After curing, use a matching punch to drill a hole in the center of the PDMS and cut it into the required shape and size. Finally, use a plasma bonding machine to bond the glass plate to the PDMS plate to seal the microfluidic channel.

[0082] S2, Reference Figure 3 Preparation of Fe3O4@SiO2 core-shell nanoparticles:

[0083] S2-1. Preparation of Fe3O4 nanoparticles: Take 12g of ferric chloride hexahydrate and 18g of trisodium citrate dihydrate, and dissolve them completely in ethylene glycol (EG). Stir magnetically for 1.5h, then add 0.9g of sodium acetate and continue stirring for another 8h. After the reagents have fully reacted, pour the mixture into a stainless steel autoclave lined with a polytetrafluoroethylene inner cylinder and heat at 200℃ for 10h. After cooling to room temperature, remove the supernatant, collect the prepared Fe3O4 nanoparticles using a permanent magnet, transfer them to a beaker, and bring the volume to a final volume.

[0084] S2-2, Preparation of Fe3O4@SiO2 core-shell nanoparticles: The Fe3O4 nanoparticles prepared in S2-1 were uniformly dispersed in a three-necked sphere containing concentrated ammonia and anhydrous ethanol. The mixture was heated and mechanically stirred for 30 min in a water bath. Tetraethyl silicate (TEOS) was added dropwise, and stirring was continued for 12 h after the addition was complete. After the reaction was completed, the supernatant was removed, and the obtained Fe3O4@SiO2 core-shell nanoparticles were collected by magnetic separation, washed, and diluted to a fixed volume.

[0085] S3. Reference Figure 4 Preparation of thermal alarm (HA) microcapsules:

[0086] S3-1. Preparation of melamine-formaldehyde (MF) prepolymer: Weigh 4g of formaldehyde and 2.5g of melamine into a three-necked flask, mix with 100mL of deionized water, stir magnetically to mix thoroughly, then add triethanolamine to adjust the pH of the mixture to 8-9 to carry out the polymerization reaction, and heat in a constant temperature water bath at 50℃ for 20min to obtain the MF prepolymer.

[0087] S3-2. Preparation of a homogeneous oil-water mixture:

[0088] S3-2-1. Preparation of oil phase: Weigh 5g of 1-hexadecanool, 0.2g of bisphenol A, and 0.1g of fluorescent red (HFG) into a three-necked flask and mechanically stir in a constant temperature water bath at 75℃ for 30min to obtain the oil phase.

[0089] S3-2-2 Preparation of aqueous phase: Weigh 1g of styrene-maleic anhydride copolymer (SMA), 0.5g of sodium hydroxide and 95mL of deionized water, and stir magnetically at 60℃ for 60min to obtain the aqueous phase.

[0090] S3-2-3. Preparation of a homogeneous oil-water system: The oil phase is slowly added to the aqueous phase, and citric acid solution is added dropwise to adjust the pH of the mixture to 5.5. The mixture is then heated in a constant temperature water bath at 70°C for 30 minutes to obtain a homogeneous oil-water system.

[0091] S3-3, Preparation of HA microcapsules: The prepared MF prepolymer was slowly pumped into a homogeneous oil-water system at a rate of 1 mL / min. Under a constant temperature water bath at 70℃, citric acid was added dropwise to a three-necked flask at a rate of 0.3 mL / min to adjust the pH of the mixture to 4.2, and the mixture was heated in the water bath for 1 hour. Sodium hydroxide solution was added dropwise to the mixture to adjust the pH to neutral, and then the mixture was stirred continuously for 20 minutes before heating was stopped. After cooling to room temperature, the suspension was filtered, washed, and dried to obtain HA microcapsule powder. The entire process is as follows: Figure 4 As shown.

[0092] S4, Reference Figure 5 Prepare thermal alarm self-healing (HASH) microcapsules with a double-layer nested structure:

[0093] S4-1. Preparation of water / oil / solid composite emulsion

[0094] S4-1-1 Preparation of aqueous phase: At room temperature, take 120 mL of deionized water into a beaker, place it on a magnetic stirrer, add 6 g of gum arabic (GA) during stirring, and stir for another 2.5 hours until the GA is completely dissolved.

[0095] S4-1-2, Preparation of the oil phase: Weigh 4.5g toluene diisocyanate (TDI), 10.3g chlorobenzene (CB), 13.5g isophorone diisocyanate (IPDI), and 9g HA microcapsule powder prepared in S3-3. Dissolve the weighed TDI in CB and stir magnetically for 15 minutes. After the solid is completely dissolved, add the weighed IPDI and HA microcapsule powder and mix them evenly to obtain an oil-solid blend.

[0096] S4-1-3. Preparation of the composite emulsion: Extract the aqueous phase using two syringes and the oil phase using one syringe. Assemble the syringes with their matching flexible tubing and stainless steel needles, and place the syringes on a peristaltic pump, inserting the needle into the orifice of the microfluidic device. Adjust the flow rate of the aqueous phase to 200 μL / min and the flow rate of the oil phase to 50 μL / min, and finally collect the resulting water / oil / solid composite emulsion with a uniform diameter.

[0097] S4-2, Preparation of HASH microcapsules: 0.45g of the prepared Fe3O4@SiO2 nanoparticles were added to the composite emulsion prepared in S4-1-3 and ultrasonically dispersed for 3h. The mixture was then placed in a 50℃ oil bath and magnetically stirred. 3.2g of 1,4-butanediol was slowly added dropwise, and the mixture was stirred for 10-20min. The oil bath temperature was then increased to 70℃ and the reaction was stirred for 1.5h to obtain a suspension. After the suspension cooled to room temperature, it was repeatedly washed three times with deionized water, separated by decanting, and filtered through a Bukner funnel. Finally, it was air-dried in a cool place to obtain HASH microcapsules.

[0098] S5. Characterization tests on the morphological characteristics of HASH microcapsules: The size distribution of microdroplets obtained by traditional mechanical stirring and microfluidic methods was compared with that obtained by optical microscopy and particle size analyzer; the morphology and particle size of microcapsules were observed by SEM and the particle size distribution of microcapsules was obtained by statistical software; the functional groups of microcapsules were tested and analyzed by Fourier transform infrared spectroscopy; the thermal stability of microcapsules was analyzed by thermogravimetric analysis, and finally a series of properties of microcapsules were obtained.

[0099] The size, morphology, and distribution of microdroplets obtained by traditional mechanical stirring and microfluidic methods were compared using optical microscopy and a particle size analyzer. Figure 6 (Where: (a) is an optical image of mechanically stirred microdroplets, and (b) is an optical image of microfluidic microdroplets) and Figure 7 (Where: (a) represents the particle size distribution of mechanically stirred microdroplets, and (b) represents the particle size distribution of microfluidically prepared microdroplets.) As shown in the figure, the droplets prepared by microfluidic control have a narrower diameter distribution, concentrated in the range of 220–240 μm, and the probability of this distribution gradually decreases along the average particle size distribution. In contrast, the droplets obtained by mechanical stirring have a non-uniform particle size distribution, ranging from 50 to 300 μm. Therefore, microfluidically prepared microdroplets exhibit better monodispersity, facilitating the formation of microcapsules.

[0100] Observing the microcapsules and their shells using a scanning electron microscope, such as... Figure 8 (a) is a SEM image of the HASH microcapsule, and (b) is a SEM image of the HASH microcapsule shell. As shown in the figures, the prepared microcapsules are complete spheres, undamaged, uniform in size, and with a moderate wall thickness of approximately 4 μm. This ensures good support for the core material without being too thick and affecting the release of the core material. Furthermore, the presence of even smaller microcapsules demonstrates the successful realization of a double-layered nesting of self-healing microcapsules and HA microcapsules.

[0101] The functional groups of the microcapsules were tested and analyzed using Fourier transform infrared spectroscopy, such as... Figure 9 As shown, the peaks at 1365.53 cm⁻¹, 1536.9 cm⁻¹, 1725.94 cm⁻¹, and 3394.32 cm⁻¹ are the tensile vibration absorption peaks of CO, hydrogen-bonded C=O, non-hydrogen-bonded C=O, and NH, respectively. This indicates that the microcapsules contain urethane (NHCOO) groups, thus the polyurethane shell of the HASH microcapsules was successfully formed.

[0102] The EDS distribution of the microcapsules was obtained by energy dispersive spectroscopy (EDS). Carbon, iron, and silicon were labeled with red, orange, and purple, respectively. Figure 10 As shown in the figure, the three elements are evenly distributed on the surface of the microcapsule, which fully proves the existence of Fe3O4@SiO2 core-shell nanoparticles and successfully realizes the microcapsule shell with target migration function.

[0103] Thermogravimetric analysis (TGA) was used to analyze the thermal stability of the microcapsules, and the TGA curves of the microcapsules were obtained as follows: Figure 11 As shown, the microcapsule decomposition exhibits two peaks (162℃ and 230℃), representing the decomposition temperatures of the microcapsule shell and core, respectively. Therefore, both the core material and the microcapsule possess good stability.

[0104] To characterize the successful realization of the thermal alarm and self-healing dual functions of the prepared microcapsules, the prepared HASH microcapsules can be incorporated into an insulating material matrix to observe their thermal discoloration and self-healing effects. An epoxy resin matrix is ​​used as an example here.

[0105] E51 epoxy resin, MHHPA, and 2,4,6-tap catalyst were mixed at a mass ratio of 50:10:1 to form an epoxy resin matrix. Simultaneously, the prepared HASH microcapsules were incorporated into the epoxy resin matrix at a ratio of 0.5 wt%. The mixture was magnetically stirred at low speed until uniformly dispersed. The mixture was placed in a mold and degassed under vacuum at room temperature to eliminate air bubbles. The microcapsules were guided to vulnerable areas within the material using a directional magnetic field. The magnet's position was fixed when the microcapsules were distributed in a predetermined direction until the sample cured at high temperature.

[0106] Figure 12 The figure shows the color change of the composite material during the heating-cooling cycle. As can be seen from the figure, the composite material can guarantee a stable and obvious color change.

[0107] To more clearly observe the self-healing effect after mechanical and electrical treeing damage, 0.2 vol% of fluorescent yellow 131SC dye was added to the healing agent of the microcapsules, and the results were observed under a laser scanning confocal microscope. When mechanical or electrical treeing damage progressed to the point of causing the microcapsules to rupture, the healing agent flowed into the crack channels and effectively filled them, such as... Figure 13 Fluorescent images of the mechanical damage healing effect shown and Figure 14 The fluorescence image shown demonstrates the healing effect of electrical tree damage. As can be seen from the figure, the prepared HASH microcapsules can effectively enable the composite material to self-repair.

[0108] 1. This invention successfully prepared a functionalized thermal alarm self-healing (HASH) microcapsule with a double-layer nested structure. Through the design of the double-layer nested structure, the microcapsule is made dual-functional. It can not only independently repair microscale electrical tree damage caused by electrothermal stress, but also has good thermochromic properties, which can detect local overheating of insulating materials in advance and issue timely warnings before electrical tree damage occurs. Moreover, the two functions do not affect each other.

[0109] 2. This invention successfully endows HASH microcapsules with directional traction capabilities by embedding magnetic nanoparticles in the microcapsule shell, allowing them to be precisely guided and placed in relatively fragile areas of the substrate, greatly improving repair capabilities and the sensitivity of temperature alarms.

[0110] 3. This invention successfully achieves precise control of the size of emulsion droplets through a microfluidic platform, which is beneficial for the control of microcapsule size and facilitates the practical application of microcapsules when doped with insulating materials.

[0111] The specific embodiments described herein are merely illustrative of the spirit of the invention. Those skilled in the art to which this invention pertains may make various modifications or additions to the described specific embodiments or use similar methods to substitute them, without departing from the spirit of the invention or exceeding the scope defined by the appended claims.

Claims

1. A method for preparing functionalized thermal alarm self-healing microcapsules with a double-layer nested structure based on microfluidics, characterized in that... It includes the following steps: S1. Fabrication of microfluidic devices; S2. Preparation of Fe3O4@SiO2 core-shell nanoparticles; S3. Preparation of thermal alarm HA microcapsules; S3-1. Preparation of melamine-formaldehyde MF prepolymer: Weigh melamine and formaldehyde in a mass ratio of 1-5:2-8 into a three-necked flask, mix with 100 mL of deionized water, stir magnetically to mix thoroughly, add triethanolamine to adjust the pH of the mixture to 8-9 to carry out the polymerization reaction, and heat in a constant temperature water bath at 45-55℃ for 15-25 min to obtain the MF prepolymer; S3-2. Preparation of a homogeneous oil-water mixture: S3-2-1. Preparation of oil phase: Weigh fluorescent red HFG, bisphenol A and 1-hexadecanool in a mass ratio of 1:1~3:40~60 into a three-necked flask, and mechanically stir in a constant temperature water bath at 70~80℃ for 25~35 min to obtain the oil phase; S3-2-2, Preparation of aqueous phase: Weigh styrene-maleic anhydride copolymer (SMA), sodium hydroxide, and deionized water in a mass ratio of 1:0.2~1:90~100, and magnetically stir them at 50~70℃ for 50~60 min to obtain the aqueous phase; S3-2-3. Preparation of a homogeneous oil-water system: The oil phase is slowly added to the water phase, with a mass ratio of oil phase to water phase of 5:90-100. At the same time, citric acid solution is added dropwise to adjust the pH of the mixture to 5-6. The mixture is then kept in a constant temperature water bath at 60-80℃ for 20-40 minutes to obtain a homogeneous oil-water system. S3-3, Preparation of HA microcapsules: The prepared MF prepolymer was slowly pumped into a homogeneous oil-water system at a rate of 1 mL / min, with a volume ratio of MF prepolymer to oil-water system of 1:1; under constant temperature water bath conditions of 60-80℃, citric acid was added dropwise to a three-necked flask at a rate of 0.2-0.4 mL / min to adjust the pH of the mixture to 4-5, and the mixture was heated in the water bath for 1 hour; sodium hydroxide solution was added dropwise to the mixture to adjust the pH to neutral, and then the mixture was stirred continuously for 15-30 minutes before heating was stopped. After cooling to room temperature, the suspension was filtered, washed, and dried to obtain HA microcapsule powder; S4. Preparation of thermal alarm self-healing HASH microcapsules with a double-layer nested structure: S4-1. Preparation of water / oil / solid composite emulsion: S4-1-1 Preparation of aqueous phase: At room temperature, take 110-130 mL of deionized water into a beaker, place it on a magnetic stirrer, add 5-7 g of gum arabic (GA) during stirring, and stir for 2-3 hours until the GA is completely dissolved. S4-1-2, Preparation of the oil phase: Weigh toluene diisocyanate (TDI), chlorobenzene CB, isophorone diisocyanate (IPDI), and HA microcapsule powder prepared in S3-3 in a mass ratio of 1:2.2-2.4:3:1.5-3; Dissolve the weighed TDI in CB and stir magnetically for 10-15 minutes. After the solid is completely dissolved, add the weighed IPDI and HA microcapsule powder and mix them evenly to obtain an oil-solid blend. S4-1-3. Preparation of composite emulsion: Extract the prepared aqueous phase using two syringes and the prepared oil phase using one syringe; assemble the syringes with matching soft tubing and stainless steel needles, and place the syringes on a peristaltic pump, inserting the needle into the hole at the center of the PDMS; adjust the flow rate of the aqueous phase to 150–250 μL / min and the flow rate of the oil phase to 40–60 μL / min, and finally collect the water / oil / solid composite emulsion with uniform diameter. S4-2, Preparation of HASH microcapsules: Fe3O4@SiO2 nanoparticles were added to the composite emulsion prepared in S4-1-3 and ultrasonically dispersed for 3 h. Then, the mixture was placed in an oil bath at 50 °C and magnetically stirred. 1,4-Butanediol was slowly added dropwise and stirred for 10-20 min. The oil bath temperature was then increased to 70 °C and stirred for 1-2 h to obtain a suspension. After the suspension has cooled to room temperature, rinse it repeatedly with deionized water 3 to 5 times, separate by decanting, and filter it with a Bukner funnel. Finally, air dry in a cool place to obtain HASH microcapsules.

2. The method according to claim 1, characterized in that... The fabrication of the microfluidic device in S1 specifically includes the following steps: S1-1, Preparation of microfluidic channels: First, take a certain amount of concentrated sulfuric acid solution and hydrogen peroxide in a volume ratio of 7:3, stir well, and then soak the silicon wafer in the solution for 15-20 minutes. After washing it several times with deionized water, acetone and anhydrous ethanol, blow it dry with nitrogen gas and place it on a beaker. Take another beaker and add 1-2 drops of hexamethyldisilane to it. Place both beakers in a vacuum chamber and dry for 3-5 minutes. Then, the dried silicon wafer is placed in the center of a spin coater, and 4-5 mL of SU-8-2000 photoresist is poured onto the silicon wafer. The spin coater is set to 200 r / min for 20 s and 1300 r / min for 50 s. The silicon wafer coated with photoresist is then placed on a heating stage for soft baking at 60-65°C for 6-8 min, followed by baking at 90-95°C for 40-45 min. After baking, the wafer is placed on a photomask for UV exposure for 45 s to 1 min, followed by baking at 60-65°C for 6-8 min and then baking at 90-95°C for 10-15 min to enhance the baking effect. Finally, excess photoresist was cleaned sequentially using SU-8-2000 developer, acetone, ethanol and deionized water. After drying with nitrogen, 2-3 drops of 1H1H2H2H-perfluorooctylmethyldichlorosilane were added and stored in a sealed space for more than 12 hours to obtain a silicon wafer containing microfluidic channels. S1-2, Fabrication of microfluidic devices: The polydimethylsiloxane (PDMS) prepolymer with a mass ratio of 10:1 to 1.5 and its corresponding curing agent are stirred and mixed evenly, and after defoaming in a vacuum drying oven, it is poured onto the silicon wafer prepared in S1-1. The silicon wafer coated with PDMS is cured in an oven at 50 to 55°C for 3 to 4 hours. After curing, use the included punch to drill a hole in the center of the PDMS and cut it into the required shape and size; Finally, a plasma bonding machine was used to bond the glass plate to the PDMS plate to seal the microfluidic channel.

3. The method according to claim 1, characterized in that... The preparation of Fe3O4@SiO2 core-shell nanoparticles in S2 specifically includes the following steps: S2-1. Preparation of Fe3O4 nanoparticles: Take ferric chloride hexahydrate, trisodium citrate dihydrate, and sodium acetate in a mass ratio of 4:6:0.3-0.

4. Dissolve ferric chloride hexahydrate and trisodium citrate dihydrate completely in ethylene glycol (EG). Stir magnetically for 1-2 hours, then add sodium acetate and continue stirring for 8-9 hours. After the reagents have fully reacted, pour the mixture into a stainless steel autoclave lined with a polytetrafluoroethylene inner cylinder and heat at 180-220°C for 10-11 hours. When it cools to room temperature, remove the supernatant, collect the prepared Fe3O4 nanoparticles using a permanent magnet, transfer them to a beaker, and bring the volume to a final volume. S2-2, Preparation of Fe3O4@SiO2 core-shell nanoparticles: The Fe3O4 nanoparticles prepared in S2-1 were uniformly dispersed in a slanted three-necked sphere containing concentrated ammonia and anhydrous ethanol. The mixture was heated and mechanically stirred for 30 min under water bath conditions. Tetraethyl silicate (TEOS) was added dropwise, and stirring was continued for 12-13 h after the addition was complete. After the reaction was completed, the supernatant was removed, and the obtained Fe3O4@SiO2 core-shell nanoparticles were collected by magnetic separation, washed, and diluted to a fixed volume.

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